The document summarizes the first observations of the magnetic Kelvin-Helmholtz instability in the solar corona using high-resolution imaging from NASA's Solar Dynamics Observatory. The instability was detected on the northern flank of a fast coronal mass ejection, appearing as substructures or waves against the darker coronal background. Analysis found the observed phase speed of the waves to be about half the speed of the ejecta front, validating theories of the non-linear dynamics of this instability in magnetized plasma environments. The findings provide new insights into fundamental plasma processes in the solar atmosphere and solar-terrestrial system.
Geomagnetism and paleomagnetism are the two main divisions of magnetism in geophysics and geology. Geomagnetism deals with using magnetism to explore subsurface structures like minerals, basement rocks, and salt domes. Paleomagnetism studies the history of Earth's magnetic field and poles to understand rock histories and plate tectonics. Magnetism in rocks comes from ferromagnetic minerals like magnetite aligning their atomic magnets to retain magnetization even after the magnetic field is removed. This remanent magnetization can provide information about ancient field orientations and plate motions.
This paper analyzes photographic observations of the 1995 Quadrantid meteor shower made by the Dutch Meteor Society. The orbits of 95 Quadrantid meteors were precisely measured from photographic plates, providing the highest accuracy orbital data yet for this stream. Analysis of the orbits shows that the dispersion is much less than previous studies, indicating that the main component of the Quadrantid stream is only about 500 years old, much younger than the 5000-7500 years assumed previously. This suggests that the main peak arises from a recent "outburst" rather than the classical dust component. The stream likely does not originate from comet 96P/Machholz 1 as thought, and its true parent body may be an asteroid-like object in a
Quantitative and Qualitative Seismic Interpretation of Seismic Data Haseeb Ahmed
This document discusses quantitative and qualitative seismic interpretation techniques used to analyze seismic data and map subsurface geology. It compares traditional qualitative techniques to more modern quantitative techniques. It then focuses on unconventional seismic interpretation techniques used for unconventional reservoirs with low permeability, including AVO analysis, seismic inversion, seismic attributes, and forward seismic modeling. These techniques can help identify tight gas, shale gas, and gas hydrate reservoirs that conventional methods cannot easily detect. The document provides details on how each technique works and its advantages.
Saturn’s magnetic field revealed by the Cassini Grand FinaleSérgio Sacani
Starting on 26 April 2017,
the Grand Finale phase of the Cassini mission
took the spacecraft through the gap between
Saturn’s atmosphere and the inner edge of its
innermost ring (the D-ring) 22 times, ending
with a final plunge into the atmosphere on
15 September 2017. This phase offered an opportunity
to investigate Saturn’s internal magnetic
field and the electromagnetic environment
between the planet and its rings. The internal
magnetic field is a diagnostic of interior structure,
dynamics, and evolution of
the host planet. Rotating convective
motion in the highly electrically
conducting layer of the planet
is thought to maintain the magnetic
field through the magnetohydrodynamic
(MHD) dynamo
process. Saturn’s internal magnetic
field is puzzling because of its
high symmetry relative to the spin
axis, known since the Pioneer 11
flyby. This symmetry prevents an
accurate determination of the rotation
rate of Saturn’s deep interior
and challenges our understanding
of the MHD dynamo process because
Cowling’s theorem precludes
a perfectly axisymmetric magnetic
field being maintained through an
active dynamo.
There are two main types of volcanic earthquakes: 1) volcano-tectonic earthquakes, which occur due to stress changes in rock from magma movement and can cause land subsidence and cracks, but do not necessarily indicate an impending eruption. 2) long-period earthquakes, which result from pressure changes due to sustained magma injection and indicate volcanic activity is underway or an eruption may be imminent. Volcanic tremors detected prior to eruptions at Mount St. Helens and Pinatubo have successfully warned of eruptions. Structures should be earthquake-resistant and built away from unstable slopes to prevent damage from volcanic quakes.
2D Seismic Data Interpretation and Volumetric Analyis of Dhulain Area, Upper ...Fasih Akhtar
This document summarizes a student's thesis on interpreting 2D seismic data and conducting volumetric analysis of the Dhulian area in the Upper Indus Basin of Pakistan. The objectives were to map the subsurface structure through seismic interpretation, prepare time and depth sections, analyze well data from Dhulian-43, and calculate the remaining oil potential. Key findings included that the Dhulian structure is a thrust-bounded, salt-cored anticline compartmentalized by faults. Reservoir analysis of the Chorgali and Lockhart formations showed good porosity and hydrocarbon saturation. Estimated original oil in place was 65-175 million barrels depending on the scenario. More data was recommended to better define the structure.
C.K. Morley a,⇑, A. Alvey b
a Department of Geological Sciences, Chiang Mai University, Chiang Mai 50200, Thailand
b Badley Geoscience Ltd., North Beck House, North Beck Lane, Hundelby, Spilsby, Lincolnshire PE23 5NB, UK
Geomagnetism and paleomagnetism are the two main divisions of magnetism in geophysics and geology. Geomagnetism deals with using magnetism to explore subsurface structures like minerals, basement rocks, and salt domes. Paleomagnetism studies the history of Earth's magnetic field and poles to understand rock histories and plate tectonics. Magnetism in rocks comes from ferromagnetic minerals like magnetite aligning their atomic magnets to retain magnetization even after the magnetic field is removed. This remanent magnetization can provide information about ancient field orientations and plate motions.
This paper analyzes photographic observations of the 1995 Quadrantid meteor shower made by the Dutch Meteor Society. The orbits of 95 Quadrantid meteors were precisely measured from photographic plates, providing the highest accuracy orbital data yet for this stream. Analysis of the orbits shows that the dispersion is much less than previous studies, indicating that the main component of the Quadrantid stream is only about 500 years old, much younger than the 5000-7500 years assumed previously. This suggests that the main peak arises from a recent "outburst" rather than the classical dust component. The stream likely does not originate from comet 96P/Machholz 1 as thought, and its true parent body may be an asteroid-like object in a
Quantitative and Qualitative Seismic Interpretation of Seismic Data Haseeb Ahmed
This document discusses quantitative and qualitative seismic interpretation techniques used to analyze seismic data and map subsurface geology. It compares traditional qualitative techniques to more modern quantitative techniques. It then focuses on unconventional seismic interpretation techniques used for unconventional reservoirs with low permeability, including AVO analysis, seismic inversion, seismic attributes, and forward seismic modeling. These techniques can help identify tight gas, shale gas, and gas hydrate reservoirs that conventional methods cannot easily detect. The document provides details on how each technique works and its advantages.
Saturn’s magnetic field revealed by the Cassini Grand FinaleSérgio Sacani
Starting on 26 April 2017,
the Grand Finale phase of the Cassini mission
took the spacecraft through the gap between
Saturn’s atmosphere and the inner edge of its
innermost ring (the D-ring) 22 times, ending
with a final plunge into the atmosphere on
15 September 2017. This phase offered an opportunity
to investigate Saturn’s internal magnetic
field and the electromagnetic environment
between the planet and its rings. The internal
magnetic field is a diagnostic of interior structure,
dynamics, and evolution of
the host planet. Rotating convective
motion in the highly electrically
conducting layer of the planet
is thought to maintain the magnetic
field through the magnetohydrodynamic
(MHD) dynamo
process. Saturn’s internal magnetic
field is puzzling because of its
high symmetry relative to the spin
axis, known since the Pioneer 11
flyby. This symmetry prevents an
accurate determination of the rotation
rate of Saturn’s deep interior
and challenges our understanding
of the MHD dynamo process because
Cowling’s theorem precludes
a perfectly axisymmetric magnetic
field being maintained through an
active dynamo.
There are two main types of volcanic earthquakes: 1) volcano-tectonic earthquakes, which occur due to stress changes in rock from magma movement and can cause land subsidence and cracks, but do not necessarily indicate an impending eruption. 2) long-period earthquakes, which result from pressure changes due to sustained magma injection and indicate volcanic activity is underway or an eruption may be imminent. Volcanic tremors detected prior to eruptions at Mount St. Helens and Pinatubo have successfully warned of eruptions. Structures should be earthquake-resistant and built away from unstable slopes to prevent damage from volcanic quakes.
2D Seismic Data Interpretation and Volumetric Analyis of Dhulain Area, Upper ...Fasih Akhtar
This document summarizes a student's thesis on interpreting 2D seismic data and conducting volumetric analysis of the Dhulian area in the Upper Indus Basin of Pakistan. The objectives were to map the subsurface structure through seismic interpretation, prepare time and depth sections, analyze well data from Dhulian-43, and calculate the remaining oil potential. Key findings included that the Dhulian structure is a thrust-bounded, salt-cored anticline compartmentalized by faults. Reservoir analysis of the Chorgali and Lockhart formations showed good porosity and hydrocarbon saturation. Estimated original oil in place was 65-175 million barrels depending on the scenario. More data was recommended to better define the structure.
C.K. Morley a,⇑, A. Alvey b
a Department of Geological Sciences, Chiang Mai University, Chiang Mai 50200, Thailand
b Badley Geoscience Ltd., North Beck House, North Beck Lane, Hundelby, Spilsby, Lincolnshire PE23 5NB, UK
An Integrated Study of Gravity and Magnetic Data to Determine Subsurface Stru...iosrjce
:The present study wascarried out to delineate the location, extension, trend and depth of subsurface
structures of Alamein area. To achieve this aim, the gravity and aeromagnetic data have been subjected to
different analytical techniques. The Fast Fourier Transform technique was used to separatethe residual
components from the regional ones. The resulted maps showed that the area was affected mainly bytheENE, EW,
WNWand NWtectonic trends. In addition, spectral analysis technique was applied on magnetic anomalies to
estimate the depth to basement surface, which varies from 3.03 in southern part to 7.24 Km in northern part.3DEulerdeconvloution
and tilt angle derivative techniques were carried out to detect the edges of magnetic sources
and to determine their depths.Correlation between them shows acoincidence between Euler solution and zero
lines of tilt angle map. A tentative basement structure map is constructed from the integration of these results
and geological information. This map shows alternative uplifted and downfaulted structure trending in the ENE,
NE and E-W directions. In addition, the NNW to NW strike-slip faults intersected them in later events. Finally,
2-D modeling technique was run on three gravity and magnetic profiles in the same location. Different drilled
wells and the constructed basement structure map support these modeled profiles. Theyshow an acidic basement
rocks. A general decreasing of Conrad discontinuity depths from about 20.5 km at southern part to 17.9 km at
northern part can be noticed. Moreover, the crustal thickness (depth to Moho discontinuity), varies between
31.5 and 28.5 km revealing visibly crustal stretching and thinning northerly
The document summarizes findings from orbital magnetic field measurements taken by the MESSENGER spacecraft around Mercury. Key points:
1) Remanent magnetization has been detected in Mercury's crust, providing evidence that Mercury had a dynamo-generated magnetic field early in its history.
2) The magnetization is estimated to have an average age of 3.7-3.9 billion years, based on its presence across diverse terrain including the youngest volcanic deposits on Mercury.
3) Ancient field strengths that could have produced the observed magnetization range from Mercury's current dipole field strength to values similar to Earth's ancient field.
This document summarizes recent research on the North Anatolian Fault in Turkey. Key points include:
- The fault has been active since the Miocene period 15 million years ago, with an average slip rate of 0.5-0.7 cm/year. The recent slip rate associated with earthquakes is 1-2 cm/year.
- Stress drops from earthquakes on the fault are not dependent on magnitude for quakes above M7. Relationships between seismic moment and fault area differ for large and small quakes.
- Future research needs include more detailed mapping, paleogeographic reconstruction, geochemical correlations across the fault, seismic studies, and geodetic monitoring for earthquake prediction.
Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with ...Sérgio Sacani
On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter,
passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s
poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather
features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow
low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared
mapping reveals the relative humidity within prominent downwelling regions. Juno’s
measured gravity field differs substantially from the last available estimate and is one
order of magnitude more precise. This has implications for the distribution of heavy
elements in the interior, including the existence and mass of Jupiter’s core. The observed
magnetic field exhibits smaller spatial variations than expected, indicative of a rich
harmonic content.
predicting the long term solar wind ion-sputtering source at mercuryJay Kim
This document summarizes research predicting the long-term solar wind ion-sputtering source at Mercury using data from the Helios spacecraft. The key points are:
1) Maps of solar wind proton flux onto Mercury's surface were constructed using a magnetosphere model and solar wind conditions estimated from Helios data when it was in Mercury's orbit.
2) Analysis of Helios data in Mercury's orbital range found that solar wind density increases by a factor of 2.3 from aphelion to perihelion, while velocity is independent of distance. IMF Bz is more likely to be strongly southward at perihelion.
3) Model runs used solar wind parameters matching the most probable conditions identified
Temporal Variations in Earth's Magnetic FieldShivam Shekhar
A presentation discussing various kinds of temporal variations in Earth's magnetic field such as geomagnetic secular variations, geomagnetic excursions, geomagnetic reversals, geomagnetic storms and apparent polar wander along with the genesis of the Sun and the Earth.
1) Simple 2D magnetic and gravity models were constructed for the Marmara Sea region using geophysical data.
2) The magnetic models show fault-related magnetic bodies extending from the sea floor to a depth of 14.5 km.
3) The gravity model is consistent with previous seismic maps and shows horst-like structures in the central ridge, suggesting the area acts as a restraining bend.
Alma observations of_the_transition_from_infall_motion_to_keplerian_rotation_...Sérgio Sacani
We have observed the Class I protostar TMC-1A with Atacama Millimeter/submillimeter
Array (ALMA) in the emissions of 12CO and C18O (J = 2−1),
and 1.3-mm dust continuum. Continuum emission with a deconvolve size of
0.
′′50 × 0.
′′37, perpendicular to the 12CO outflow, is detected. It most likely traces
a circumstellar disk around TMC-1A, as previously reported. In contrast, the
C
18O a more extended structure is detected in C18O although it is still elongated
with a deconvolved size of 3.
′′3 × 2.
′′2, indicating that C18O traces mainly a flattened
envelope surrounding the disk and the central protostar. C
18O shows a
clear velocity gradient perpendicular to the outflow at higher velocities, indicative
of rotation, while an additional velocity gradient along the outflow is found
at lower velocities. The radial profile of the rotational velocity is analyzed in
detail, finding that it is given as a power-law ∝ r
−a with an index of ∼ 0.5 at
higher velocities. This indicates that the rotation at higher velocities can be
explained as Keplerian rotation orbiting a protostar with a dynamical mass of
0.68 M⊙ (inclination corrected). The additional velocity gradient of C18O along
the outflow is considered to be mainly infall motions in the envelope. PositionVelocity
diagrams made from models consisting of an infalling envelope and a
Keplerian disk are compared with the observations, revealing that the observed
infall velocity is ∼0.3 times smaller than free fall velocity yielded by the dynamical
mass of the protostar. Magnetic fields could be responsible for the slow infall
velocity. A possible scenario of Keplerian disk formation is discussed.
This document summarizes the tectonic and stratigraphic evolution of the Sarulla graben geothermal area in North Sumatra, Indonesia. It discusses the regional tectonic setting involving strike-slip movement along the Sumatra Fault zone. Exploration efforts in the Sarulla contract area provided data on the fault geometry and displacement history, as well as the Quaternary volcanic history. Four geothermal systems in the area are closely associated with major faults and volcanic centers. The oldest exposed rocks are late Paleozoic metasediments, overlain by Miocene marine sediments to the east. Younger units include Plio-Pleistocene volcanic rocks from centers along the Sumatra Fault zone that fill the Sarulla
The magnetic method detects near-surface ferrous materials by measuring anomalies in the Earth's magnetic field. When ferrous objects are placed in the magnetic field, they develop an induced magnetic field that is superimposed on the Earth's field, creating a detectable anomaly. The method works best for detecting buried ferrous metals and can be used to map geology and locate buried infrastructure through magnetic susceptibility variations in rocks.
Photometry of Giant Propellers in Saturn's RingsJakaylaRobinson
1) The document discusses analyzing images of "giant propellers" in Saturn's rings taken by Cassini during its Ring Grazing Orbit and Grand Finale.
2) The authors use images of the propeller "Santos-Dumont" taken on the lit and unlit sides to investigate how the propeller's brightness relates to its optical depth, by comparing predicted and observed brightness values.
3) They find the brightness ratio between prediction and observation is consistent in translucent parts of the propeller and ring, but varies more in opaque parts, helping evaluate differences between empty and opaque regions.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
This document discusses using calcite twinning analysis to quantify the principal paleostress magnitudes during the Indosinian orogeny in central Thailand. The study uses data from the Khao Khwang fold-thrust belt to determine differential stress magnitudes for each tectonic stage. Combining these stress estimates with geochronological data constrains the timing of burial depth changes and folding within the belt. The proposed tectonic scenario is based on the sequenced fracturing, faulting, and folding of strata during the Indosinian orogeny.
An extremely high_altitude_plume_seen_at_mars_morning_terminatorSérgio Sacani
Artigo da revista Nature que descreve as plumas de alta altitude identificadas pairando sobre a superfície do planeta Marte e propõem duas hipóteses para o fenômeno.
Edge Detectionand Depth Estimation from Magnetic DataofWadi Araba,Eastern Des...iosrjce
Edge detection, trend analysis and depth estimation techniques are very important steps in the
interpretation of magnetic anomalies. In this paper, the Fast Fourier Transform was applied to showing the
regional and residual sources. Trend analysis was carried out on the Reduced to Pole, regional and residual
aeromagnetic maps to delineate the main tectonic trends dissected the study area. The edges of these sources
is determined by using the tilt angle derivative and standard 3D-Euler deconvolution. The estimated Euler
solutions was plotted on the tilt angle derivative map. A good correlation was noticed between them
indicating that both of them can be contribute in delineating the general structural framework of the area.
These techniques indicate that Wadi Araba is highly affected by the Gulf of Suez rifting system and the Syrian
Arc folding system. On other hand, the area is affected by the Tethyan trend especially the southwestern
corner of this area and it is maintained in regional components. The depth estimation was applied using
analytic signal and Source Parameter imaging techniques. These depth methods show a comparable results.
The depth to the top of the basement sources ranges from about 200 to 4000 m.
This document summarizes a study that performed broadband frequency simulations of strong ground motion in the Sea of Marmara region of Turkey based on fault rupture scenarios. Three earthquake scenarios were modeled involving rupture of the Central Marmara Fault and North Boundary Fault, which pose the largest hazard to Istanbul. A hybrid technique was used that combines deterministic and semi-stochastic methods. The location of the hypocenter was found to be a critical parameter for predicting ground motions in Istanbul. Anelasticity was also found to significantly affect regional attenuation of peak ground accelerations. The simulated ground motions resulted in large acceleration response spectra at long periods that could be critical for building damage in Istanbul during an actual earthquake.
S/C in Heliosynchronous Orbit - Spacecraft Environment AnalysisPau Molas Roca
The document characterizes the space radiation environment for a spacecraft in a heliosynchronous orbit at 800 km altitude. It finds that the main radiation sources are solar particles, trapped radiation in the Van Allen belts, and galactic cosmic rays. The radiation can damage spacecraft devices through single-event effects and dielectric charging. The worst scenarios include higher radiation in the South Atlantic Anomaly and polar regions due to weaker magnetic shielding.
This document compares estimates of slip rates from long-term seismicity data to those calculated from GPS measurements for three regions in the eastern Mediterranean: the Gulf of Corinth, the Sea of Marmara, and the Dead Sea Fault Zone. It finds that slip rates calculated from historical earthquake data are generally comparable to those from GPS, while also quantifying uncertainties in the size of historical earthquakes. This permits a more reliable estimation of long-term seismic hazard for engineering purposes. The study focuses on areas with extensive long-term macroseismic information to facilitate this type of analysis.
Supermassive black holes do not correlate with galaxy disks or pseudobulgesSérgio Sacani
The document summarizes research finding that supermassive black holes do not correlate with galaxy disks or pseudobulges. It finds that black hole mass correlates strongly with classical bulges, which are indistinguishable from elliptical galaxies, but correlates little or not at all with pseudobulges or disks. This suggests two different modes of black hole feeding - rapid growth driven by mergers for classical bulges, and slower local growth for pseudobulges and disks.
Brazil has a long history in astronomy dating back to the 17th century when the first astronomical observatory was founded in Recife. Astronomy grew slowly over the centuries and accelerated in recent decades due to new funding, graduate programs, and infrastructure like the OPD telescope. Brazil now participates in international observatories like Gemini, SOAR, and CFHT to give its astronomers access to a wide range of telescopes. The national astronomical community has grown rapidly to over 650 scientists spread across 46 institutions nationwide. Brazil also develops astronomical instrumentation through organizations like LNA and INPE.
An Integrated Study of Gravity and Magnetic Data to Determine Subsurface Stru...iosrjce
:The present study wascarried out to delineate the location, extension, trend and depth of subsurface
structures of Alamein area. To achieve this aim, the gravity and aeromagnetic data have been subjected to
different analytical techniques. The Fast Fourier Transform technique was used to separatethe residual
components from the regional ones. The resulted maps showed that the area was affected mainly bytheENE, EW,
WNWand NWtectonic trends. In addition, spectral analysis technique was applied on magnetic anomalies to
estimate the depth to basement surface, which varies from 3.03 in southern part to 7.24 Km in northern part.3DEulerdeconvloution
and tilt angle derivative techniques were carried out to detect the edges of magnetic sources
and to determine their depths.Correlation between them shows acoincidence between Euler solution and zero
lines of tilt angle map. A tentative basement structure map is constructed from the integration of these results
and geological information. This map shows alternative uplifted and downfaulted structure trending in the ENE,
NE and E-W directions. In addition, the NNW to NW strike-slip faults intersected them in later events. Finally,
2-D modeling technique was run on three gravity and magnetic profiles in the same location. Different drilled
wells and the constructed basement structure map support these modeled profiles. Theyshow an acidic basement
rocks. A general decreasing of Conrad discontinuity depths from about 20.5 km at southern part to 17.9 km at
northern part can be noticed. Moreover, the crustal thickness (depth to Moho discontinuity), varies between
31.5 and 28.5 km revealing visibly crustal stretching and thinning northerly
The document summarizes findings from orbital magnetic field measurements taken by the MESSENGER spacecraft around Mercury. Key points:
1) Remanent magnetization has been detected in Mercury's crust, providing evidence that Mercury had a dynamo-generated magnetic field early in its history.
2) The magnetization is estimated to have an average age of 3.7-3.9 billion years, based on its presence across diverse terrain including the youngest volcanic deposits on Mercury.
3) Ancient field strengths that could have produced the observed magnetization range from Mercury's current dipole field strength to values similar to Earth's ancient field.
This document summarizes recent research on the North Anatolian Fault in Turkey. Key points include:
- The fault has been active since the Miocene period 15 million years ago, with an average slip rate of 0.5-0.7 cm/year. The recent slip rate associated with earthquakes is 1-2 cm/year.
- Stress drops from earthquakes on the fault are not dependent on magnitude for quakes above M7. Relationships between seismic moment and fault area differ for large and small quakes.
- Future research needs include more detailed mapping, paleogeographic reconstruction, geochemical correlations across the fault, seismic studies, and geodetic monitoring for earthquake prediction.
Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with ...Sérgio Sacani
On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter,
passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s
poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather
features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow
low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared
mapping reveals the relative humidity within prominent downwelling regions. Juno’s
measured gravity field differs substantially from the last available estimate and is one
order of magnitude more precise. This has implications for the distribution of heavy
elements in the interior, including the existence and mass of Jupiter’s core. The observed
magnetic field exhibits smaller spatial variations than expected, indicative of a rich
harmonic content.
predicting the long term solar wind ion-sputtering source at mercuryJay Kim
This document summarizes research predicting the long-term solar wind ion-sputtering source at Mercury using data from the Helios spacecraft. The key points are:
1) Maps of solar wind proton flux onto Mercury's surface were constructed using a magnetosphere model and solar wind conditions estimated from Helios data when it was in Mercury's orbit.
2) Analysis of Helios data in Mercury's orbital range found that solar wind density increases by a factor of 2.3 from aphelion to perihelion, while velocity is independent of distance. IMF Bz is more likely to be strongly southward at perihelion.
3) Model runs used solar wind parameters matching the most probable conditions identified
Temporal Variations in Earth's Magnetic FieldShivam Shekhar
A presentation discussing various kinds of temporal variations in Earth's magnetic field such as geomagnetic secular variations, geomagnetic excursions, geomagnetic reversals, geomagnetic storms and apparent polar wander along with the genesis of the Sun and the Earth.
1) Simple 2D magnetic and gravity models were constructed for the Marmara Sea region using geophysical data.
2) The magnetic models show fault-related magnetic bodies extending from the sea floor to a depth of 14.5 km.
3) The gravity model is consistent with previous seismic maps and shows horst-like structures in the central ridge, suggesting the area acts as a restraining bend.
Alma observations of_the_transition_from_infall_motion_to_keplerian_rotation_...Sérgio Sacani
We have observed the Class I protostar TMC-1A with Atacama Millimeter/submillimeter
Array (ALMA) in the emissions of 12CO and C18O (J = 2−1),
and 1.3-mm dust continuum. Continuum emission with a deconvolve size of
0.
′′50 × 0.
′′37, perpendicular to the 12CO outflow, is detected. It most likely traces
a circumstellar disk around TMC-1A, as previously reported. In contrast, the
C
18O a more extended structure is detected in C18O although it is still elongated
with a deconvolved size of 3.
′′3 × 2.
′′2, indicating that C18O traces mainly a flattened
envelope surrounding the disk and the central protostar. C
18O shows a
clear velocity gradient perpendicular to the outflow at higher velocities, indicative
of rotation, while an additional velocity gradient along the outflow is found
at lower velocities. The radial profile of the rotational velocity is analyzed in
detail, finding that it is given as a power-law ∝ r
−a with an index of ∼ 0.5 at
higher velocities. This indicates that the rotation at higher velocities can be
explained as Keplerian rotation orbiting a protostar with a dynamical mass of
0.68 M⊙ (inclination corrected). The additional velocity gradient of C18O along
the outflow is considered to be mainly infall motions in the envelope. PositionVelocity
diagrams made from models consisting of an infalling envelope and a
Keplerian disk are compared with the observations, revealing that the observed
infall velocity is ∼0.3 times smaller than free fall velocity yielded by the dynamical
mass of the protostar. Magnetic fields could be responsible for the slow infall
velocity. A possible scenario of Keplerian disk formation is discussed.
This document summarizes the tectonic and stratigraphic evolution of the Sarulla graben geothermal area in North Sumatra, Indonesia. It discusses the regional tectonic setting involving strike-slip movement along the Sumatra Fault zone. Exploration efforts in the Sarulla contract area provided data on the fault geometry and displacement history, as well as the Quaternary volcanic history. Four geothermal systems in the area are closely associated with major faults and volcanic centers. The oldest exposed rocks are late Paleozoic metasediments, overlain by Miocene marine sediments to the east. Younger units include Plio-Pleistocene volcanic rocks from centers along the Sumatra Fault zone that fill the Sarulla
The magnetic method detects near-surface ferrous materials by measuring anomalies in the Earth's magnetic field. When ferrous objects are placed in the magnetic field, they develop an induced magnetic field that is superimposed on the Earth's field, creating a detectable anomaly. The method works best for detecting buried ferrous metals and can be used to map geology and locate buried infrastructure through magnetic susceptibility variations in rocks.
Photometry of Giant Propellers in Saturn's RingsJakaylaRobinson
1) The document discusses analyzing images of "giant propellers" in Saturn's rings taken by Cassini during its Ring Grazing Orbit and Grand Finale.
2) The authors use images of the propeller "Santos-Dumont" taken on the lit and unlit sides to investigate how the propeller's brightness relates to its optical depth, by comparing predicted and observed brightness values.
3) They find the brightness ratio between prediction and observation is consistent in translucent parts of the propeller and ring, but varies more in opaque parts, helping evaluate differences between empty and opaque regions.
Geophysical prospecting uses physical methods to study the structure of the Earth's crust and locate minerals and ores. It involves collecting data using geophysical methods like seismic, gravitational, magnetic, electrical, and electromagnetic surveys. Seismic methods are commonly used in exploration. They involve generating seismic waves using sources like sledgehammers and analyzing the reflected and refracted waves detected by receivers to characterize subsurface layers and locate resources based on their elastic properties. Proper data acquisition, processing to reduce noise, and geological interpretation of processed seismic data are required to build an accurate model of the subsurface.
This document discusses using calcite twinning analysis to quantify the principal paleostress magnitudes during the Indosinian orogeny in central Thailand. The study uses data from the Khao Khwang fold-thrust belt to determine differential stress magnitudes for each tectonic stage. Combining these stress estimates with geochronological data constrains the timing of burial depth changes and folding within the belt. The proposed tectonic scenario is based on the sequenced fracturing, faulting, and folding of strata during the Indosinian orogeny.
An extremely high_altitude_plume_seen_at_mars_morning_terminatorSérgio Sacani
Artigo da revista Nature que descreve as plumas de alta altitude identificadas pairando sobre a superfície do planeta Marte e propõem duas hipóteses para o fenômeno.
Edge Detectionand Depth Estimation from Magnetic DataofWadi Araba,Eastern Des...iosrjce
Edge detection, trend analysis and depth estimation techniques are very important steps in the
interpretation of magnetic anomalies. In this paper, the Fast Fourier Transform was applied to showing the
regional and residual sources. Trend analysis was carried out on the Reduced to Pole, regional and residual
aeromagnetic maps to delineate the main tectonic trends dissected the study area. The edges of these sources
is determined by using the tilt angle derivative and standard 3D-Euler deconvolution. The estimated Euler
solutions was plotted on the tilt angle derivative map. A good correlation was noticed between them
indicating that both of them can be contribute in delineating the general structural framework of the area.
These techniques indicate that Wadi Araba is highly affected by the Gulf of Suez rifting system and the Syrian
Arc folding system. On other hand, the area is affected by the Tethyan trend especially the southwestern
corner of this area and it is maintained in regional components. The depth estimation was applied using
analytic signal and Source Parameter imaging techniques. These depth methods show a comparable results.
The depth to the top of the basement sources ranges from about 200 to 4000 m.
This document summarizes a study that performed broadband frequency simulations of strong ground motion in the Sea of Marmara region of Turkey based on fault rupture scenarios. Three earthquake scenarios were modeled involving rupture of the Central Marmara Fault and North Boundary Fault, which pose the largest hazard to Istanbul. A hybrid technique was used that combines deterministic and semi-stochastic methods. The location of the hypocenter was found to be a critical parameter for predicting ground motions in Istanbul. Anelasticity was also found to significantly affect regional attenuation of peak ground accelerations. The simulated ground motions resulted in large acceleration response spectra at long periods that could be critical for building damage in Istanbul during an actual earthquake.
S/C in Heliosynchronous Orbit - Spacecraft Environment AnalysisPau Molas Roca
The document characterizes the space radiation environment for a spacecraft in a heliosynchronous orbit at 800 km altitude. It finds that the main radiation sources are solar particles, trapped radiation in the Van Allen belts, and galactic cosmic rays. The radiation can damage spacecraft devices through single-event effects and dielectric charging. The worst scenarios include higher radiation in the South Atlantic Anomaly and polar regions due to weaker magnetic shielding.
This document compares estimates of slip rates from long-term seismicity data to those calculated from GPS measurements for three regions in the eastern Mediterranean: the Gulf of Corinth, the Sea of Marmara, and the Dead Sea Fault Zone. It finds that slip rates calculated from historical earthquake data are generally comparable to those from GPS, while also quantifying uncertainties in the size of historical earthquakes. This permits a more reliable estimation of long-term seismic hazard for engineering purposes. The study focuses on areas with extensive long-term macroseismic information to facilitate this type of analysis.
Supermassive black holes do not correlate with galaxy disks or pseudobulgesSérgio Sacani
The document summarizes research finding that supermassive black holes do not correlate with galaxy disks or pseudobulges. It finds that black hole mass correlates strongly with classical bulges, which are indistinguishable from elliptical galaxies, but correlates little or not at all with pseudobulges or disks. This suggests two different modes of black hole feeding - rapid growth driven by mergers for classical bulges, and slower local growth for pseudobulges and disks.
Brazil has a long history in astronomy dating back to the 17th century when the first astronomical observatory was founded in Recife. Astronomy grew slowly over the centuries and accelerated in recent decades due to new funding, graduate programs, and infrastructure like the OPD telescope. Brazil now participates in international observatories like Gemini, SOAR, and CFHT to give its astronomers access to a wide range of telescopes. The national astronomical community has grown rapidly to over 650 scientists spread across 46 institutions nationwide. Brazil also develops astronomical instrumentation through organizations like LNA and INPE.
A closely packed system of low mass, low-density planets transiting kepler-11Sérgio Sacani
The document summarizes the discovery of six transiting exoplanets orbiting the star Kepler-11. Photometry from the Kepler spacecraft revealed periodic dips in the star's brightness consistent with multiple transiting planets. Six planetary candidates were identified, with orbital periods ranging from 10 to 47 days for the inner five planets. Radial velocity measurements confirmed the planetary nature of the five inner planets and allowed for mass estimates. The outermost sixth planet was also validated as a planet. Analysis of the transit times, durations and depths provided insights into the properties, dynamics, and stability of this unique six-planet system.
A mechanism for the present day creation of a new class of black holesSérgio Sacani
This document proposes a mechanism for the formation of new classes of black holes with masses less than 2 solar masses (substellar mass dwarf black holes or DBHs) in the expanding gases of astrophysical phenomena like supernovae. It presents a heuristic method for determining gravitational instability and collapse in non-spherical matter distributions, which could allow detection of regions in simulation data that form DBHs. Applying this method to a Type II supernova simulation, the authors found regions with densities and masses close to what is needed to form DBHs. Future work will estimate the mass spectrum and abundances of ejected and bound DBHs.
Polarized gamma ray emission from the galactic black hole cygnus x-1Sérgio Sacani
Polarized gamma-ray emission was measured from the black hole binary system Cygnus X-1 using the INTEGRAL/IBIS telescope. Spectral modeling revealed two emission components: 250-400 keV emission consistent with Compton scattering and weakly polarized; 400 keV - 2 MeV emission from a power law component that is strongly polarized at 67%, likely from synchrotron emission in the jet. The polarization angle of 140° is significantly different than the radio jet angle, as seen in other jet sources.
Titan is a moon of Saturn with a dense nitrogen-methane atmosphere that allows for organic chemistry on its surface. The Cassini mission and Huygens probe provided data about Titan's surface, which appears to have liquid methane and ethane at some point in its history. Evidence suggests Titan has an internal liquid water layer that allows geological activity like cryovolcanism, and that ammonia plays a key role in maintaining this layer and Titan's evolution.
Zero outward flow velocity for plasma in a heliosheath transition layeSérgio Sacani
The document summarizes recent findings from Voyager 1, which has been traveling through the heliosheath region between the solar wind termination shock and the heliopause boundary. Key findings include:
1) The radial velocity of plasma detected by Voyager 1 has decreased nearly linearly from 70 km/s to 0 km/s over the past 3 years and has remained at 0 km/s for the past 8 months, indicating Voyager 1 has entered a transition layer with zero radial flow.
2) This transition layer was not predicted by models and contradicts expectations of an abrupt discontinuity at the heliopause.
3) Analysis of plasma velocity measurements suggests Voyager 1 may have crossed the he
The high albedo of the hot jupiter kepler 7 bSérgio Sacani
This document summarizes the analysis of Kepler photometry data for the exoplanet Kepler-7b. Key findings include:
1) The occultation depth is measured to be 44±5 ppm, translating to a Kepler geometric albedo of 0.32±0.03, the most precise value measured for an exoplanet.
2) The planetary orbital phase lightcurve is characterized with an amplitude of 42±4 ppm.
3) Atmospheric modeling finds it unlikely that the high albedo is due to a dominant thermal component. Two possible explanations are proposed: excess reflection from clouds/hazes, or depleted atmospheric sodium and potassium allowing Rayleigh scattering to dominate.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
A massive protocluster of galaxies at a redshift of z<5.3Sérgio Sacani
This document describes the discovery of a massive protocluster of galaxies located approximately 1 billion years after the Big Bang (redshift of z=5.3). The protocluster contains overdense regions of massive galaxies extending over 13 megaparsecs. It contains an extremely luminous starburst galaxy with large molecular gas reserves and a luminous quasar. Together, these objects place a minimum total mass of over 4×1011 solar masses in this early cluster, consistent with cosmological simulations of the earliest galaxy clusters. This discovery provides evidence for the hierarchical formation of massive structures in the early universe.
1) The Fermi bubbles are giant gamma-ray emitting structures extending above and below the galactic center.
2) The bubbles may have been formed by periodic capture of stars by the supermassive black hole at the galactic center, releasing energy of around 3x10^52 ergs per capture.
3) This energy injection could produce very hot plasma, accelerating electrons that produce radio and gamma-ray emission through synchrotron radiation and inverse Compton scattering.
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
The auroral footprint of enceladus on saturn nature09928Sérgio Sacani
The document reports the detection of magnetic-field-aligned ion and electron beams downstream of Enceladus, indicating electrodynamic coupling between Enceladus and Saturn similar to Io and Jupiter. Auroral ultraviolet emission was observed in Saturn's ionosphere at the footprint location of Enceladus, varying in intensity more than can be explained by changes in magnetospheric parameters alone and likely indicating variable plume activity on Enceladus. The footprint latitude matches predictions based on Saturn's magnetic field model. Flickering of the electron beams between different energy levels was also observed and may be related to standing Alfven waves driven by Enceladus.
Herman mosquera2011 nonlinear electrodynamics and the pioneer 1011 spacecraftSOCIEDAD JULIO GARAVITO
1) The document discusses the unexplained "Pioneer anomaly" - an anomalous blueshift in radio signals from the Pioneer 10/11 spacecraft that suggests they are accelerating under an unexplained force.
2) Conventional explanations like gravitational effects, solar radiation pressure, and modified dynamics have been ruled out. The anomaly appears to be related to the electromagnetic sector rather than gravity.
3) The document proposes that nonlinear electrodynamics (NLED), where the electromagnetic field depends nonlinearly on the field strength, could explain an anomalous frequency shift in photons as they propagate through space without interacting with matter. This effect is called "photon acceleration".
Discovery of powerful gamma ray flares from the crab nebulaSérgio Sacani
1) The AGILE satellite detected powerful gamma-ray flares from the Crab Nebula in September 2010 and October 2007 that increased the nebula's unpulsed gamma-ray flux by a factor of 3.
2) The flares originated near the nebula's central pulsar and challenge standard models of nebular emission.
3) Synchrotron emission from shock-accelerated electrons along the pulsar's polar jet can explain the gamma-ray flaring, requiring particle acceleration on timescales of about 1 day.
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely with previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years.
Giant magnetized outflows from the centre of the Milky WayCarlos Bella
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely to previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years. The ridges
Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rar...Sérgio Sacani
Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasisatellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on
centennial timescales, maintaining this dynamics over megayears. The similarity of its
reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated
from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of
particles launched from different locations on the lunar surface with a range of ejection
velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment
from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon
environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a
small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s
orbit. The most favored conditions are launch velocities slightly above the escape velocity
from the trailing lunar hemisphere.
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
This document discusses the recycling of magnetic flux in the quiet Sun's corona. It presents a study that uses magnetogram observations to track photospheric magnetic flux fragments over time and models their evolution using a potential field approximation. The main findings are:
1) The quiet Sun's coronal flux is generally recycled on much shorter timescales, around 3 hours, than the corresponding recycling timescale of photospheric flux, which is around 8-19 hours.
2) When also considering emergence and cancellation of photospheric flux, the net replacement time of coronal flux is estimated to be only 1.4 hours.
3) The amount of magnetic reconnection driven by the motions and interactions of photospheric
This document summarizes an analysis of high resolution infrared spectra from the Cassiopeia A supernova remnant taken by the Spitzer Space Telescope. The analysis finds:
1) The reverse shock of the remnant is spherical to within 7%, though offset from the geometric center by 810 km/s.
2) Nucleosynthetic layers of Si and O show velocities differing by up to 500 km/s in some directions, indicating separation during the supernova.
3) Small-scale corrugated velocity structures seen in the ejecta likely formed during the supernova rather than by later instabilities at the remnant's reverse shock.
Fleeting Small-scale Surface Magnetic Fields Build the Quiet-Sun CoronaSérgio Sacani
Arch-like loop structures filled with million Kelvin hot plasma form the building blocks of the quiet-Sun corona.
Both high-resolution observations and magnetoconvection simulations show the ubiquitous presence of magnetic
fields on the solar surface on small spatial scales of ∼100 km. However, the question of how exactly these quietSun coronal loops originate from the photosphere and how the magnetic energy from the surface is channeled to
heat the overlying atmosphere is a long-standing puzzle. Here we report high-resolution photospheric magnetic
field and coronal data acquired during the second science perihelion of Solar Orbiter that reveal a highly dynamic
magnetic landscape underlying the observed quiet-Sun corona. We found that coronal loops often connect to
surface regions that harbor fleeting weaker, mixed-polarity magnetic field patches structured on small spatial
scales, and that coronal disturbances could emerge from these areas. We suggest that weaker magnetic fields with
fluxes as low as 1015 Mx and/or those that evolve on timescales less than 5 minutes are crucial to understanding
the coronal structuring and dynamics.
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
1) Cassini images of Saturn's infrared aurora show emission both poleward and equatorward of the main auroral oval, unlike previous ultraviolet observations.
2) The polar emission is highly variable but sometimes as bright as the main oval; it disappears when the main oval has a spiral shape.
3) An arc of emission exists equatorward of the main oval only on the nightside, suggesting internal magnetospheric processes drive this previously unknown current system.
1) Newly-born pulsars offer favorable conditions for accelerating heavy nuclei like iron to ultrahigh energies via unipolar induction. However, these nuclei must escape the surrounding dense supernova envelope.
2) The paper analytically and numerically examines the escape of ultrahigh energy cosmic rays (UHECRs) from supernova envelopes. It finds that at early times when protons could reach energies above 10^20 eV, the envelope prevents their escape. However, heavier iron nuclei can still reach the highest observed energies at later times when the envelope has thinned.
3) The authors conclude that a small fraction (0.01%) of extragalactic rapidly rotating young pulsars embedded in supernov
1) Global climate models that include sophisticated cloud schemes show that tidally locked planets can develop thick water clouds near the substellar point due to strong convection. These clouds greatly increase the planetary albedo and stabilize temperatures, allowing habitability at twice the stellar flux previously thought possible.
2) The cloud feedback is stabilizing, as higher stellar flux produces stronger convection and higher albedos. Substellar clouds can block outgoing radiation, reducing the day-night temperature contrast.
3) Non-tidally locked planets do not experience this stabilizing cloud feedback, as clouds only form over parts of the tropics and mid-latitudes. Their albedo decreases with increasing stellar flux, producing a destabil
The article discusses observations from multiple space-based observatories that tracked a sun-diving comet, C/2011 N3 (SOHO), as it passed through the Sun's corona and disintegrated. The observatories captured details of the comet's flight path, emissions, and disintegration over time. Studying how comets interact with and break apart in the corona can provide insights into comet composition and the early solar system.
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
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)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
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Ca-rich population. Although such an object is too red for any low-
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cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
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) with
Λ
CDM. Therefore unlike low-
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Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
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truly diverge from their low-
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counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Climate extremes likely to drive land mammal extinction during next supercont...
Foullon preprint apjl_2011
1. Magnetic Kelvin-Helmholtz Instability at the Sun
Claire Foullon
Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4
7AL, UK
claire.foullon@warwick.ac.uk
Erwin Verwichte
Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4
7AL, UK
Valery M. Nakariakov
Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4
7AL, UK
Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 St Petersburg,
Russia
Katariina Nykyri
Department of Physical Sciences, Embry-Riddle Aeronautical University, Daytona Beach, FL 32114, USA
and
Charles J. Farrugia
Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824, USA
ABSTRACT
Flows and instabilities play a major role in the dynamics of magnetised plasmas including
the solar corona, magnetospheric and heliospheric boundaries, cometary tails and astrophysical
jets. The non-linear effects, multi-scale and microphysical interactions inherent to the flow-driven
instabilities are believed to play a role, e.g., in plasma entry across a discontinuity, generation of
turbulence and enhanced drag. However, in order to clarify the efficiency of macroscopic insta-
bilities in these processes, we lack proper knowledge of their overall morphological features. Here
we show the first observations of the temporally and spatially resolved evolution of the magnetic
Kelvin-Helmholtz instability in the solar corona. Unprecedented high-resolution imaging obser-
vations of vortices developing at the surface of a fast coronal mass ejecta are taken by the new
Solar Dynamics Observatory, validating theories of the non-linear dynamics involved. The new
findings are a corner stone for developing a unifying theory on flow-driven instabilities in rarefied
magnetised plasmas, important to shed light on the fundamental processes at work in key regions
of the Sun-Earth system.
Subject headings: instabilities — plasmas — solar-terrestrial relations — Sun: corona — Sun: coronal
mass ejections (CMEs) — Sun: oscillations
Accepted 20 January 2011 for publication in Astrophysical Journal Letters
1
2. Flow-driven instabilities typically arise at flow
shear boundaries, and are accompanied by en-
ergy transfer. A classical example is the Kelvin-
Helmholtz (KH) instability, which occurs when
two fluids flow at different velocities parallel to
a surface of discontinuity with a strong enough
shear to overcome the restraining surface tension
force. The phenomenon is well understood in fluid
and gas dynamics, but is much more challeng-
ing in magnetised plasmas typical of space and
astrophysical environments, where the 3-d topol-
ogy and various conditions of the rarefied plasma
introduce additional constraints and control the
characteristics of the resulting disturbances that
Fig. 1.— Fast coronal mass ejecta erupting from
overcome the magnetic tension force of the curved
the Sun, with KH waves detected on its North-
field lines. At the terrestrial magnetopause, the
ern flank. The SDO/AIA image, shown in solar-
archetypal natural example of an interface be-
centred X (increasing towards West) versus Y (in-
tween two plasma regions in sheared flow, a num-
creasing towards North) coordinates, is taken in
ber of instabilities may mediate plasma transfer,
the 131˚ channel and centred on the ejecta lift-
A
mixing and energisation. The KH instability is
ing off the South-East solar limb. With increas-
one that operates on the magnetopause (Hasegawa
ing (brighter) intensity levels, it shows the ejecta
1975) with large-scale consequences for its dynam-
canopy and within it, a brighter core above a
ics (e.g., Farrugia et al. 1998; Nykyri & Otto 2001).
thinner ‘reconnecting’ current sheet. The overlaid
The instability is believed to be operative in other
rectangular ROI indicates the Northern flank re-
planetary environments of the solar system (e.g.,
gion, where substructures, corresponding to the
Amerstorfer et al. 2007; Sundberg et al. 2010, and
presumed KH waves, are detected against the
references therein). Many theories have also ex-
darker coronal background, and which is used to
plored whether it could occur at fast-slow stream
construct the time-distance image plot in Figure
interfaces at the Sun or in the solar wind (Ko-
2.
rzhov et al. 1984; Joarder et al. 1997; Suess et al.
2009). Moreover, in flow channels, it is invoked
in various solar structures (e.g., Karpen et al. tory before. These capabilities are provided by
1993; Ofman et al. 1994; Andries & Goossens 2001; the Atmospheric Imaging Assembly (AIA) (Lemen
Lapenta et al. 2003; Berger et al. 2010; Ryutova et al. 2010) on board the Solar Dynamics Obser-
et al. 2010), planetary magnetotails (e.g., McKen- vatory (SDO), which images the Sun (since end
zie 1970), cometary tails (e.g., Ershkovich 1980), of March 2010) in ten white light, ultraviolet and
astrophysical sources, such as jets in active galac- extreme ultraviolet (EUV) bandpasses, covering a
tic nuclei and around stellar mass black holes (e.g., wide range of temperatures, at an unprecedented
Ferrari et al. 1981; Stella & Rosner 1984). high temporal cadence (up to 10-20 s) and spatial
And yet, for an instability so important in resolution (0.6” per pixel).
space, solar and astrophysical plasma environ- The CME event occurred on November 3 2010,
ments, it has not been possible to find convinc- following a C4.9 GOES class flare (peaking at
ing imaging observational evidence of the over- 12:15:09 UT from active region NOAA 11121, lo-
all morphological features in the development of cated near the South-East solar limb). The insta-
this instability. New capabilities for studying the bility is detected in the highest AIA temperature
Sun allow us to detect and image KH waves for channel only, centered on the 131˚ EUV bandpass
A
the first time, in a fast Coronal Mass Ejection at 11 MK. In this temperature range, the ejecta
(CME) event where the instability develops at lifting off from the solar surface forms a bubble of
the flank of the CME ejecta, and with resolutions enhanced emission against the lower density coro-
unmatched in any other natural plasma labora- nal background, as shown in Figure 1. Along the
2
3. 170 SDO/AIA 131Å
150
m s-1 h
833 k
130
Distance (Mm)
110
λ
s-1
417 km
90
70
50
30
0 12 24 36 48 60 72 84 96
Time (sec) from 2010-11-03 12:14:45.62 UT
Fig. 2.— Development of KH waves on the upper ejecta flank region. Snapshots of the ROI overlaid in
Figure 1 are taken every 12 s and are directed vertically with increasing distance above the solar surface. To
improve the contrast, the intensity is shown relative to a background intensity profile, decreasing with height.
This background profile is taken as a running smooth average of the vertical profile obtained from averaging
all the ROI images in the horizontal direction. In this time-distance image, the slope of the upper dashed line
connecting ejecta front radial positions over time indicates the speed of the ejecta front; the lower slope of
the long-dashed lines connecting related substructures indicates an observational ‘phase speed’, Vk, which is
about half the former ejecta front speed. The waves are coherent and non-dispersive, with regular separation
distances corresponding to wavelength λ, as indicated between two long-dashed lines. One structure is seen
to develop to an indicated maximum height h within less than 36 s.
Northern flank of the ejecta, a train of three to four locity of the wave envelope or group speed, Vk , is
substructures forms a regular pattern in the inten- about half the ejecta front speed, Vejecta , which
sity contrast. Figure 2 shows several snapshots, may be seen to correspond to limiting cases ex-
taken every 12s, of this Northern ejecta flank re- pected from linear theory (Chandrasekhar 1961;
gion, when the substructures are seen to develop. Hasegawa 1975).
The direction along the ejecta flank is oriented The CME flow environment and geometry may
vertically and indicated with distance above the be compared to those of the archetypal planetary
solar surface. The resulting time-distance image magnetosphere, with a common onset of the KH
allows us to derive the speed of the ejecta front, instability prescribed by the flow shear directions
Vejecta = 833 ± 5 km s−1 (projected in the plane of and the density differences between environments,
the sky) and to infer that the substructures are co- as sketched in Figure 3 (panels a and b). While the
herent, non-dispersive, perturbations that propa- instability is expected on both sides of the mag-
gate with observational ‘phase speed’, Vk = 417±7 netopause for similar magnetic field orientations,
km s−1 . The distance between substructures cor- some helical configuration of the canopy field can
respond to a projected wavelength λ = 18 ± 0.4 explain here why the phenomena could be ob-
Mm. Thus the period of these perturbations is served on one flank of the ejecta only. This helical
43 ± 2 s. We interpret these perturbations as configuration may be localised (Srivastava et al.
KH waves. Considering the convectively unsta- 2010) during the finite time (30 ± 6s) over which
ble surface mode (Mills et al. 2000), perturba- the instability is observed to develop, which would
tions along the boundary surface, while growing, be short enough in comparison with the Alfv´nice
are convected downstream with the corresponding time for the helical twist to be smoothed out.
group velocity. The (projected) propagation ve-
3
4. a b
c
B corona B magnetosphere
ck
E sho
CM ath
sh e
e
E
us
CM opy a
can ne top
cta M ag th
je h ea
tos
E
ne ck
M ag ho
Bo ws
B IMF
Solar ejecta B ejecta Near-Earth solar wind
Fig. 3.— Sketch of comparison of the KH instability conditions in two key regions of the Sun-Earth system,
(a) the CME and (b) the Magnetosphere, with (c) close-up view on a KH vortex illustrated by numerical
simulations (Nykyri et al. 2006). Purple and orange colours indicate low and high plasma density levels.
Flow vectors are shown in (c). In the low density regions (purple) being compared: (b) the equatorial cross-
section of the magnetosphere is shown with the Earth’s (almost) dipolar magnetospheric field as viewed from
the North; in (a), by analogy, the plane of sky where the waves are detected is shown with the magnetic
field canopy of the corona, best represented parallel to the solar surface, pointing in the same direction. In
the high density regions (orange) being compared: (b) the best conditions for the KH instability to occur
are those of magnetosheath field lines (draped IMF lines around the magnetopause) parallel or anti-parallel
to the Earth’s magnetospheric field, since one can align the wave vector perpendicular to these lines so as
to switch off magnetic tensions; in (a), to simplify and facilitate the comparison, the magnetic topological
configuration in and around the ejecta is stripped of the presence of current sheet(s) associated with the
active region; the ejecta canopy, formed by a magnetic field arcade of loops connected at both ends to the
Sun, is overlying a magnetic field flux rope (brightest core in Figure 1). While the instability is expected on
both sides of the magnetopause for similar magnetic field orientations, either a localised helical configuration
on one flank or a general helical configuration of the canopy field, but less favourable on the other flank, can
explain here why the phenomena could be observed on one flank of the ejecta only.
Aternatively, there may be a general helical config- tion of the CME axis has been attributed to kink
uration of the canopy field, but less favourable on instability at the onset of the eruption (Foullon
the other flank. For instance, the observed asym- et al. 2007), based on similar evidence reported
metry may be a feature of the azimuthal mode for filament eruptions with axial rotation in the
structure of the instability in the twisted field (Za- solar corona. This offers a unique opportunity to
qarashvili et al. 2010). Additionally, the observed demonstrate that the instability is indeed localised
asymmetry may simply result from the preferen- on this flank region.
tial line-of-sight viewpoint (similar to the dawn- A few rolled-up structures are visible in Fig-
dusk asymmetry caused by non-zero Interplane- ures 1 and 2. Much insight has been gained by
tary Magnetic Field (IMF) clock angles (Farrugia performing high-resolution numerical simulations,
et al. 1998; Foullon et al. 2008)). As magnetic where e.g. in its non-linear stage, the instabil-
field lines reconnect below the ejecta, the flank re- ity may set up rolled-up vortices (panel c in Fig-
gion of interest appears to rotate around the ejecta ure 3), which entrain magnetic fields of opposing
axis (starting at time + 48 s in Figure 2), so that direction (Nykyri & Otto 2004), allowing recon-
the waves are no longer visible in the coronal back- nection to occur as a secondary process and thus,
ground contrast but can still be traced as intensity for the magnetopause, allowing solar wind plasma
enhancements above the ejecta region. Such rota- to gain access to the magnetosphere (Nykyri &
4
5. Otto 2001; Hasegawa et al. 2004). By broadening tory deflections or even axial rotations (while it
the magnetopause boundary layer (Foullon et al. may be noted that the shedding of vortices behind
2008), a layer of mixed magnetospheric and solar an obstacle can generate quasi-periodic transverse
wind plasmas just inside and adjacent to the main motions (Nakariakov et al. 2009; Gruszecki et al.
current sheet, the KH mechanism contributes also 2010)).
to enhance diffusion onto closed field lines (Miura Also noted here is the occurrence of the in-
1984; Phan et al. 1997; Farrugia et al. 2001). How- stability in the hottest AIA temperature channel.
ever, many of the details of these processes, how Further detailed examination of the magnetic KH
they operate, how they ‘evolve’ in time and space instability will be undertaken in future. For in-
and their importance to the formation of boundary stance, we note that dissipation, i.e.thermal con-
layers and the global dynamics of e.g. the magne- duction or viscosity, enhanced in high-temperature
tospheric system are not fully understood. Using plasmas, may have the effect of lowering the in-
theoretical investigations of the non-linear dynam- stability threshold (Ruderman et al. 1996; Joarder
ics involved by means of magnetohydrodynamics et al. 1997). The range of favourable conditions for
(MHD) numerical simulations (Miura 1984), the the instability to occur and be visible, in combi-
initial total thickness of the velocity shear layer nation with the issuing wave characteristics that
at the fast ejecta interface is inferred to be of the are observed (period, wavelength, growth rate),
order of ∆L = 2.25 ± 1.5 Mm (the fastest grow- means that the instability needs the energy range,
ing KH modes occur at wavelength approximately time and spatial resolutions offered by SDO/AIA
6 to 12 times ∆L). The SDO/AIA images show and could not have been observed with previously
the formation of a structure reaching size h ∼ 10 available instruments. The discovery of the KH in-
Mm, which developed in 30 ± 6s (Figure 2), that is stability in the solar corona enables to deepen our
with exponential growth rate, γ = 0.05 ± 0.03 s−1 understanding of the 3-d geometrical conditions
(using ∆L as the initial size). This result is con- of instability onset, the non-linear evolution and
sistent with predicted linear growth rates (Miura its consequences for anomalous viscosity. From a
1984) that are greater than 0.1 × Vejecta /∆L for broader point of view, the combined observational
magnetosonic Mach numbers Mf ≥ 0.8, implying and theoretical characterisation and the compari-
a realistic Alfv´n speed VA ≤ 918 km s−1 (for the
e son between related solar and terrestrial phenom-
sound speed of ∼ 504 km s−1 at 11 MK), and is the ena allow us to foster a cross-fertilisation between
first ever direct validation of this theory. the fields and is a promising way to understand
An important consequence of the presence of the basic plasma physics process at work in flow-
KH vortices at CME ejecta (canopy) surfaces is driven macroscopic instabilities common to space,
their effect on the total drag force, which af- solar and astrophysical plasma environments.
fects the CME kinematics and hence its geo-
effectiveness (e.g., Foullon et al. 2007). The C.F. acknowledges financial support from the
drag on plasma flows caused by convecting vortex UK Science and Technology Facilities Council
structures is indicated by an anomalous viscosity (STFC) on the CFSA Rolling Grant. AIA data
(Miura 1984). For a transverse flow to magnetic is courtesy of SDO (NASA) and the AIA consor-
field geometry, the inferred eddy viscosity is of the tium.
order of νano ∼ 1.2 × 10−2 ∆LVejecta /2 ∼ 2 × 1014
Facilities: SDO (AIA).
erg cm2 s−1 , which is an order of magnitude larger
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