The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.
Variations in the amount of water ice on Ceres’ surface suggest a seasonal wa...Sérgio Sacani
The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were
detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed
from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation
with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months,
which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres’ orbital parameters,
points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres’ surface
indicates that this body is chemically and physically active at the present time.
Water ice is thought to be trapped in large permanently shadowed regions in the Moon’s polar regions, due to their extremely
low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the
areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the
contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for
water ice. Approximately 10–20% of the permanent cold-trap area for water is found to be contained in these micro cold traps,
which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the
number of cold traps over previous estimates, for a total area of ~40,000 km2, about 60% of which is in the south. A majority of
cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to
support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible
as a resource for future missions than previously thought.
Molecular water detected on the sunlit Moon by SOFIASérgio Sacani
Widespread hydration was detected on the lunar surface
through observations of a characteristic absorption feature
at 3 µm by three independent spacecraft1–3
. Whether the
hydration is molecular water (H2O) or other hydroxyl (OH)
compounds is unknown and there are no established methods to distinguish the two using the 3 µm band4. However, a
fundamental vibration of molecular water produces a spectral
signature at 6 µm that is not shared by other hydroxyl compounds5
. Here, we present observations of the Moon at 6 µm
using the NASA/DLR Stratospheric Observatory for Infrared
Astronomy (SOFIA). Observations reveal a 6 µm emission
feature at high lunar latitudes due to the presence of molecular water on the lunar surface. On the basis of the strength
of the 6 µm band, we estimate abundances of about 100 to
400 µg g−1
H2O. We find that the distribution of water over the
small latitude range is a result of local geology and is probably
not a global phenomenon. Lastly, we suggest that a majority of
the water we detect must be stored within glasses or in voids
between grains sheltered from the harsh lunar environment,
allowing the water to remain on the lunar surface.
Water vapor mapping on mars using omega mars expressAwad Albalwi
A systematic mapping of water vapor on Mars has been achieved using the imaging spectrometer OMEGA aboard the Mars Express
spacecraft, using the depth of the 2.6 mm (n1, n3) band of H2O. We report results obtained during two periods: (1) Ls ¼ 330–401
(January–June 2004), before and after the equinox, and (2) Ls ¼ 90–1251, which correspond to early northern summer
Exposed subsurface ice sheets in the Martian mid-latitudesSérgio Sacani
Thick deposits cover broad regions of the Martian mid-latitudes with a smooth mantle; erosion
in these regions creates scarps that expose the internal structure of the mantle.We
investigated eight of these locations and found that they expose deposits of water ice that
can be >100 meters thick, extending downward from depths as shallow as 1 to 2 meters below
the surface.The scarps are actively retreating because of sublimation of the exposed water
ice.The ice deposits likely originated as snowfall during Mars’ high-obliquity periods and have
now compacted into massive, fractured, and layered ice.We expect the vertical structure of
Martian ice-rich deposits to preserve a record of ice deposition and past climate.
This article documents the use of portable georadar for measuring the thickness of sea ice.
This device was developed to replace the method for measuring ice thickness by drilling ice
holes. The device based on the use of the LOZA georadar (ground penetrating radar, GPR)
and a specially developed method of field measurements when landing on the studied ice
formations. The study of the thickness and structure of sea ice by radar method is a complex
problem. The salinity of sea ice determines its significant conductivity, which, in turn, causes
a large attenuation of the electromagnetic signal of the georadar. The widespread GPR with
a pulse power of 50–100 W are not applicable for sounding sea ice precisely because of the
large signal attenuation. The LOZA instrument is equipped with a transmitter with a pulse
power of 1 MW. This is, on average, 10,000 times greater than that of “traditional” GPRs.
Multiple measurements of the thickness of ice formations, carried out on the one-year ice of the
eastern shelf of Sakhalin Island during winter expeditions of 2016 and 2019, have shown that
the device can quickly, accurately and with a high spatial resolution measure the thickness of
both flat and highly deformed ice (hummocks, rafted ice, and rubble field) over large areas.
KEYWORDS: Sea ice thickness; ice formations; georadar; GPR.
Variations in the amount of water ice on Ceres’ surface suggest a seasonal wa...Sérgio Sacani
The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were
detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed
from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation
with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months,
which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres’ orbital parameters,
points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres’ surface
indicates that this body is chemically and physically active at the present time.
Water ice is thought to be trapped in large permanently shadowed regions in the Moon’s polar regions, due to their extremely
low temperatures. Here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the
areas where ice may accumulate. Using theoretical models and data from the Lunar Reconnaissance Orbiter, we estimate the
contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for
water ice. Approximately 10–20% of the permanent cold-trap area for water is found to be contained in these micro cold traps,
which are the most numerous cold traps on the Moon. Consideration of all spatial scales therefore substantially increases the
number of cold traps over previous estimates, for a total area of ~40,000 km2, about 60% of which is in the south. A majority of
cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to
support ice accumulation. Our results suggest that water trapped at the lunar poles may be more widely distributed and accessible
as a resource for future missions than previously thought.
Molecular water detected on the sunlit Moon by SOFIASérgio Sacani
Widespread hydration was detected on the lunar surface
through observations of a characteristic absorption feature
at 3 µm by three independent spacecraft1–3
. Whether the
hydration is molecular water (H2O) or other hydroxyl (OH)
compounds is unknown and there are no established methods to distinguish the two using the 3 µm band4. However, a
fundamental vibration of molecular water produces a spectral
signature at 6 µm that is not shared by other hydroxyl compounds5
. Here, we present observations of the Moon at 6 µm
using the NASA/DLR Stratospheric Observatory for Infrared
Astronomy (SOFIA). Observations reveal a 6 µm emission
feature at high lunar latitudes due to the presence of molecular water on the lunar surface. On the basis of the strength
of the 6 µm band, we estimate abundances of about 100 to
400 µg g−1
H2O. We find that the distribution of water over the
small latitude range is a result of local geology and is probably
not a global phenomenon. Lastly, we suggest that a majority of
the water we detect must be stored within glasses or in voids
between grains sheltered from the harsh lunar environment,
allowing the water to remain on the lunar surface.
Water vapor mapping on mars using omega mars expressAwad Albalwi
A systematic mapping of water vapor on Mars has been achieved using the imaging spectrometer OMEGA aboard the Mars Express
spacecraft, using the depth of the 2.6 mm (n1, n3) band of H2O. We report results obtained during two periods: (1) Ls ¼ 330–401
(January–June 2004), before and after the equinox, and (2) Ls ¼ 90–1251, which correspond to early northern summer
Exposed subsurface ice sheets in the Martian mid-latitudesSérgio Sacani
Thick deposits cover broad regions of the Martian mid-latitudes with a smooth mantle; erosion
in these regions creates scarps that expose the internal structure of the mantle.We
investigated eight of these locations and found that they expose deposits of water ice that
can be >100 meters thick, extending downward from depths as shallow as 1 to 2 meters below
the surface.The scarps are actively retreating because of sublimation of the exposed water
ice.The ice deposits likely originated as snowfall during Mars’ high-obliquity periods and have
now compacted into massive, fractured, and layered ice.We expect the vertical structure of
Martian ice-rich deposits to preserve a record of ice deposition and past climate.
This article documents the use of portable georadar for measuring the thickness of sea ice.
This device was developed to replace the method for measuring ice thickness by drilling ice
holes. The device based on the use of the LOZA georadar (ground penetrating radar, GPR)
and a specially developed method of field measurements when landing on the studied ice
formations. The study of the thickness and structure of sea ice by radar method is a complex
problem. The salinity of sea ice determines its significant conductivity, which, in turn, causes
a large attenuation of the electromagnetic signal of the georadar. The widespread GPR with
a pulse power of 50–100 W are not applicable for sounding sea ice precisely because of the
large signal attenuation. The LOZA instrument is equipped with a transmitter with a pulse
power of 1 MW. This is, on average, 10,000 times greater than that of “traditional” GPRs.
Multiple measurements of the thickness of ice formations, carried out on the one-year ice of the
eastern shelf of Sakhalin Island during winter expeditions of 2016 and 2019, have shown that
the device can quickly, accurately and with a high spatial resolution measure the thickness of
both flat and highly deformed ice (hummocks, rafted ice, and rubble field) over large areas.
KEYWORDS: Sea ice thickness; ice formations; georadar; GPR.
Remote Sensing Based Soil Moisture DetectionCIMMYT
Remote sensing –Beyond images
Mexico 14-15 December 2013
The workshop was organized by CIMMYT Global Conservation Agriculture Program (GCAP) and funded by the Bill & Melinda Gates Foundation (BMGF), the Mexican Secretariat of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA), the International Maize and Wheat Improvement Center (CIMMYT), CGIAR Research Program on Maize, the Cereal System Initiative for South Asia (CSISA) and the Sustainable Modernization of the Traditional Agriculture (MasAgro)
Deep Penetration Radar. Exploration of Geological Substructures. Experimental...Leonid Krinitsky
When developing the "Loza" deep penetration radar, great efforts were taken to make the device's sounding depth attractive for geologists and geophysicists. Loza’s deep penetration radar has the following characteristics; ultrahigh power, signal energy concentration in the low-frequency spectrum area, large dynamic range of reflected signal recording [1], enabling the GPR to be applied in the exploration of subsurface structures to depths of 100-150 meters in heavy-textured low-resistivity soils and up to 200-300 meters in high-resistivity rocks.
A terrestrial planet_candidate_in_a_temperate_orbit_around_proxima_centauriSérgio Sacani
At a distance of 1.295 parsecs,1 the red-dwarf Proxima Centauri (α Centauri C, GL 551,
HIP 70890, or simply Proxima) is the Sun’s closest stellar neighbour and one of the best studied
low-mass stars. It has an effective temperature of only 3050 K, a luminosity of 0.1 per
cent solar, a measured radius of 0.14 R⊙
2 and a mass of about 12 per cent the mass of the
Sun. Although Proxima is considered a moderately active star, its rotation period is 83
days,3 and its quiescent activity levels and X-ray luminosity4 are comparable to the Sun’s. New
observations reveal the presence of a small planet orbiting Proxima with a minimum mass of
1.3 Earth masses and an orbital period of 11.2 days. Its orbital semi-major axis is 0.05 AU,
with an equilibrium temperature in the range where water could be liquid on its surface.5
Integrated Geophysical Approach for Rapid & Cost Effective Site Investigation...IEI GSC
Dr. Sanjay Rana, Director, PARSAN Overseas (P) Limited
With inputs & examples from Dr Gopal Dhawan & Dr S L Kapil
at 31st National Convention of Civil Engineers
organised by
Gujarat State Center, The Institution of Engineers (India) at Ahmedabad
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
Remote Sensing Based Soil Moisture DetectionCIMMYT
Remote sensing –Beyond images
Mexico 14-15 December 2013
The workshop was organized by CIMMYT Global Conservation Agriculture Program (GCAP) and funded by the Bill & Melinda Gates Foundation (BMGF), the Mexican Secretariat of Agriculture, Livestock, Rural Development, Fisheries and Food (SAGARPA), the International Maize and Wheat Improvement Center (CIMMYT), CGIAR Research Program on Maize, the Cereal System Initiative for South Asia (CSISA) and the Sustainable Modernization of the Traditional Agriculture (MasAgro)
Deep Penetration Radar. Exploration of Geological Substructures. Experimental...Leonid Krinitsky
When developing the "Loza" deep penetration radar, great efforts were taken to make the device's sounding depth attractive for geologists and geophysicists. Loza’s deep penetration radar has the following characteristics; ultrahigh power, signal energy concentration in the low-frequency spectrum area, large dynamic range of reflected signal recording [1], enabling the GPR to be applied in the exploration of subsurface structures to depths of 100-150 meters in heavy-textured low-resistivity soils and up to 200-300 meters in high-resistivity rocks.
A terrestrial planet_candidate_in_a_temperate_orbit_around_proxima_centauriSérgio Sacani
At a distance of 1.295 parsecs,1 the red-dwarf Proxima Centauri (α Centauri C, GL 551,
HIP 70890, or simply Proxima) is the Sun’s closest stellar neighbour and one of the best studied
low-mass stars. It has an effective temperature of only 3050 K, a luminosity of 0.1 per
cent solar, a measured radius of 0.14 R⊙
2 and a mass of about 12 per cent the mass of the
Sun. Although Proxima is considered a moderately active star, its rotation period is 83
days,3 and its quiescent activity levels and X-ray luminosity4 are comparable to the Sun’s. New
observations reveal the presence of a small planet orbiting Proxima with a minimum mass of
1.3 Earth masses and an orbital period of 11.2 days. Its orbital semi-major axis is 0.05 AU,
with an equilibrium temperature in the range where water could be liquid on its surface.5
Integrated Geophysical Approach for Rapid & Cost Effective Site Investigation...IEI GSC
Dr. Sanjay Rana, Director, PARSAN Overseas (P) Limited
With inputs & examples from Dr Gopal Dhawan & Dr S L Kapil
at 31st National Convention of Civil Engineers
organised by
Gujarat State Center, The Institution of Engineers (India) at Ahmedabad
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
Modern water at low latitudes on Mars: Potential evidence from dune surfacesSérgio Sacani
Landforms on the Martian surface are critical to understanding the nature of surface processes in the recent
past. However, modern hydroclimatic conditions on Mars remain enigmatic, as explanations for the formation
of observed landforms are ambiguous. We report crusts, cracks, aggregates, and bright polygonal ridges on the
surfaces of hydrated salt-rich dunes of southern Utopia Planitia (~25°N) from in situ exploration by the Zhurong
rover. These surface features were inferred to form after 1.4 to 0.4 million years ago. Wind and CO2 frost processes can be ruled out as potential mechanisms. Instead, involvement of saline water from thawed frost/snow is
the most likely cause. This discovery sheds light on more humid conditions of the modern Martian climate and
provides critical clues to future exploration missions searching for signs of extant life, particularly at low latitudes with comparatively warmer, more amenable surface temperatures.
Planetary-scalegiantstormserupton Saturn quasiperiodically. There have beenat least six recordedoccurrenc-es of past eruptions,and the most recentone was in 2010,withits wholelife spancaptured by the Cassinimission.In 2015,we usedthe Very LargeArray to probe the deepresponseof Saturn’s troposphere to thegiantstorms.In additionto the remnanteffectof the stormin 2010,we have foundlong-lasting signaturesof all mid-latitudegiantstorms,a mixture of equatorialstormsup to hundreds of years old, and potentiallyan unreportedolderstormat 70°N.We derive an ammoniaanomalymapthat shows an extendedmeridionalmigration of the storm’saftermath and verticaltransportof ammoniavaporby stormdynamics.Intriguingly, thelast stormin 2010splitsinto two distinctcomponentsthat propagate in oppositemeridionaldirections,leavinga gap at 43°Nplanetographiclatitude.
JWST molecular mapping and characterization of Enceladus’ water plume feeding...Sérgio Sacani
Enceladus is a prime target in the search for life in our solar system, having an active plume
likely connected to a large liquid water subsurface ocean. Using the sensitive NIRSpec
instrument onboard JWST, we searched for organic compounds and characterized the plume’s
composition and structure. The observations directly sample the fluorescence emissions of H2O
and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at
cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus'
torus. Intriguingly, the observed outgassing rate (300 kg/s) is similar to that derived from closeup observations with Cassini 15 years ago, and the torus density is consistent with previous
spatially unresolved measurements with Herschel 13 years ago, suggesting that the vigor of gas
eruption from Enceladus has been relatively stable over decadal timescales. This level of activity
is sufficient to maintain a derived column density of 4.5×1017 m-2 for the embedding equatorial
torus, and establishes Enceladus as the prime source of water across the Saturnian system. We
performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were
identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice
features, including its crystalline form, yet we do not recover CO2, CO nor NH3 ice signatures
from these observations. As we prepare to send new spacecraft into the outer solar system, these
observations demonstrate the unique ability of JWST in providing critical support to the
exploration of distant icy bodies and cryovolcanic plumes.
Artigo mostra resultados obtidos com o OSIRIS que mostra manchas brilhantes na superfície do cometa 67P/Churyumov-Gerasimenko, interpretadas como sendo gelo de água e provadas via experimentos de laboratório.
New evidence for surface water ice in small-scale cold traps and in three lar...Sérgio Sacani
The Mercury Laser Altimeter (MLA) measured surface reflectance, rs, at 1064 nm. On Mercury, most water-ice deposits have anomalously low rs values indicative of an insulating layer beneath which ice is buried. Previous detections of surface water ice (without an insulating layer) were limited to seven possible craters. Here we map rs in three additional permanently shadowed craters that host radar-bright deposits. Each crater has a mean rs value > 0.3, suggesting that water ice is exposed at the surface without an overlying insulating layer. We also identify small-scale cold traps (< 5 km in diameter) where rs > 0.3 and permanent shadows have biannual maximum surface temperatures < 100 K. We suggest that a substantial amount of Mercury’s water ice is not confined to large craters, but exists within micro-cold traps, within rough patches and inter-crater terrain.
Thermally anomalous features in the subsurface of Enceladus’s south polar ter...Sérgio Sacani
Saturn’s moon Enceladus is an active world. In 2005, the
Cassini spacecraft witnessed for the first time water-rich
jets venting from four anomalously warm fractures (called
sulci) near its south pole1,2. Since then, several observations
have provided evidence that the source of the material
ejected from Enceladus is a large underground ocean, the
depth of which is still debated3–6. Here, we report on the first
and only opportunity that Cassini’s RADAR instrument7,8 had
to observe Enceladus’s south polar terrain closely, targeting
an area a few tens of kilometres north of the active sulci.
Detailed analysis of the microwave radiometry observations
highlights the ongoing activity of the moon. The instrument
recorded the microwave thermal emission, revealing a warm
subsurface region with prominent thermal anomalies that
had not been identified before. These anomalies coincide with
large fractures, similar or structurally related to the sulci. The
observations imply the presence of a broadly distributed heat
production and transport system below the south polar terrain
with ‘plate-like’ features and suggest that a liquid reservoir
could exist at a depth of only a few kilometres under the
ice shell at the south pole. The detection of a possible dormant
sulcus further suggests episodic geological activity.
Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two
different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al.
found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit
observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks
et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is
bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows
a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness
temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal
anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid
water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect
directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface
activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface
and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial
characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered
most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the
lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in
the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with
numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30km in diameter and occurring perhaps a few million years apart. The
tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes,
which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered
highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces.
The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement
took place following a transition into a colder global climatic regime that occurred after the older
tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and
resurfacing coastal terrains.
A deep groundwater origin for recurring slope lineae on MarsSérgio Sacani
The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow
groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing
the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which
indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers
within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and
multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring
slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally
surfaces on Mars in present-day conditions.
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.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
1. Cite as: R. Orosei et al., Science
10.1126/science.aar7268 (2018).
REPORTS
First release: 25 July 2018 www.sciencemag.org (Page numbers not final at time of first release) 1
The presence of liquid water at the base of the martian polar
caps was first hypothesized more than 30 years ago (1) and
has been inconclusively debated ever since. Radio echo
sounding (RES) is a suitable technique to resolve this dispute,
because low-frequency radars have been used extensively and
successfully to detect liquid water at the bottom of terrestrial
polar ice sheets. An interface between ice and water, or alter-
natively between ice and water-saturated sediments, pro-
duces bright radar reflections (2, 3). The Mars Advanced
Radar for Subsurface and Ionosphere Sounding (MARSIS) in-
strument on the Mars Express spacecraft (4) is used to per-
form RES experiments (5). MARSIS has surveyed the martian
subsurface for more than 12 years in search of evidence of
liquid water (6). Strong basal echoes have been reported in
an area close to the thickest part of the South Polar Layered
Deposits (SPLD), Mars’ southern ice cap (7). These features
were interpreted as due to the propagation of the radar sig-
nals through a very cold layer of pure water ice having negli-
gible attenuation (7). Anomalously bright reflections were
subsequently detected in other areas of the SPLD (8).
On Earth, the interpretation of radar data collected above
the polar ice sheets is usually based on the combination of
qualitative (the morphology of the bedrock) and quantitative
(the reflected radar peak power) analyses (3, 9). The MARSIS
design, particularly the very large footprint (~3 to 5 km), does
not provide high spatial resolution, strongly limiting its abil-
ity to discriminate the presence of subglacial water bodies
from the shape of the basal topography (10). Therefore, an
unambiguous detection of liquid water at the base of the po-
lar deposit requires a quantitative estimation of the relative
dielectric permittivity (hereafter, permittivity) of the basal
material, which determines the radar echo strength.
Between 29 May 2012 and 27 December 2015, MARSIS
surveyed a 200-km-wide area of Planum Australe, centered at
193°E, 81°S (Fig. 1), which roughly corresponds to a previous
study area (8). This area does not exhibit any peculiar char-
acteristics, either in topographic data from the Mars Orbiter
Laser Altimeter (MOLA) (Fig. 1A) (11, 12) or in the available
orbital imagery (Fig. 1B) (13). It is topographically flat, com-
posed of water ice with 10 to 20% admixed dust (14, 15), and
seasonally covered by a very thin layer of CO2 ice that does
not exceed 1 m in thickness (16, 17). In the same location,
higher-frequency radar observations performed by the Shal-
low Radar instrument on the Mars Reconnaissance Orbiter
(18), revealed barely any internal layering in the SPLD and
did not detect any basal echo (fig. S1), in marked contrast
with findings for the North Polar Layer Deposits and other
regions of the SPLD (19).
A total of 29 radar profiles were acquired using the
onboard unprocessed data mode (5) by transmitting closely
spaced radio pulses centered at either 3 and 4 MHz or 4 and
5 MHz (table S1). Observations were performed when the
spacecraft was on the night side of Mars to minimize iono-
spheric dispersion of the signal. Figure 2A shows an example
Radar evidence of subglacial liquid water on Mars
R. Orosei1
*, S. E. Lauro2
, E. Pettinelli2
, A. Cicchetti3
, M. Coradini4
, B. Cosciotti2
, F. Di Paolo1
, E. Flamini4
, E.
Mattei2
, M. Pajola5
, F. Soldovieri6
, M. Cartacci3
, F. Cassenti7
, A. Frigeri3
, S. Giuppi3
, R. Martufi7
, A. Masdea8
, G.
Mitri9
, C. Nenna10
, R. Noschese3
, M. Restano11
, R. Seu7
1Istituto di Radioastronomia, Istituto Nazionale di Astrofisica, Via Piero Gobetti 101, 40129 Bologna, Italy. 2Dipartimento di Matematica e Fisica, Università degli Studi Roma
Tre, Via della Vasca Navale 84, 00146 Roma, Italy. 3Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Via del Fosso del Cavaliere 100, 00133
Roma, Italy. 4
Agenzia Spaziale Italiana, Via del Politecnico, 00133 Roma, Italy. 5
Osservatorio Astronomico di Padova, Istituto Nazionale di Astrofisica, Vicolo Osservatorio 5,
35122 Padova, Italy. 6
Consiglio Nazionale delle Ricerche, Istituto per il Rilevamento Elettromagnetico dell'Ambiente, Via Diocleziano 328, 80124 Napoli, Italy. 7
Dipartimento
di Ingegneria dell'Informazione, Elettronica e Telecomunicazioni, Università degli Studi di Roma “La Sapienza,” Via Eudossiana 18, 00184 Roma, Italy. 8E.P. Elettronica
Progetti, Via Traspontina 25, 00040 Ariccia (RM), Italy. 9International Research School of Planetary Sciences, Università degli Studi “Gabriele d'Annunzio,” Viale Pindaro 42,
65127 Pescara (PE), Italy. 10Danfoss Drives, Romstrasse 2 – Via Roma 2, 39014 Burgstall – Postal (BZ), Italy. 11Serco, c/o ESA Centre for Earth Observation, Largo Galileo
Galilei 1, 00044 Frascati (RM), Italy.
*Corresponding author. Email: roberto.orosei@inaf.it
The presence of liquid water at the base of the martian polar caps has long been suspected but not
observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for
Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft.
Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped
below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident
within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less
reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative
dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a
stable body of liquid water on Mars.
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of a MARSIS radargram collected in the area, where the sharp
surface reflection is followed by several secondary reflections
produced by the interfaces between layers within the SPLD.
The last of these echoes represents the reflection between the
ice-rich SPLD and the underlying material (hereafter, basal
material). In most of the investigated area, the basal reflec-
tion is weak and diffuse, but in some locations, it is very sharp
and has a greater intensity (bright reflections) than the sur-
rounding areas and the surface (Fig. 2B). Where the observa-
tions from multiple orbits overlap, the data acquired at the
same frequency have consistent values of both surface and
subsurface echo power (fig. S2).
The two-way pulse travel time between the surface and
basal echoes can be used to estimate the depth of the subsur-
face reflector and map the basal topography. Assuming an
average signal velocity of 170 m/μs within the SPLD, close to
that of water ice (20), the depth of the basal reflector is about
1.5 km below the surface. The large size of the MARSIS foot-
print and the diffuse nature of basal echoes outside the bright
reflectors prevent a detailed reconstruction of the basal to-
pography, but a regional slope from west to east is recogniza-
ble (Fig. 3A). The subsurface area where the bright reflections
are concentrated is topographically flat and surrounded by
higher ground, except on its eastern side, where there is a
depression.
The permittivity, which provides constraints on the com-
position of the basal material, can in principle be retrieved
from the power of the reflected signal at the base of the SPLD.
Unfortunately, the radiated power of the MARSIS antenna is
unknown because it could not be calibrated on the ground
(owing to the instrument’s large dimensions), and thus the
intensity of the reflected echoes can only be considered in
terms of relative quantities. It is common to normalize the
intensity of the subsurface echo to the surface value (21)—i.e.,
to compute the ratio between basal and surface echo power.
Such a procedure has the advantage of also compensating for
any ionospheric attenuation of the signal. Following this ap-
proach, we normalized the subsurface echo power to the me-
dian of the surface power computed along each orbit; we
found that all normalized profiles at a given frequency yield
consistent values of the basal echo power (fig. S3). Figure 3B
shows a regional map of basal echo power after normaliza-
tion; bright reflections are localized around 193°E, 81°S in all
intersecting orbits, outlining a well-defined, 20-km-wide sub-
surface anomaly.
To compute the basal permittivity, we also require infor-
mation about the dielectric properties of the SPLD, which de-
pend on the composition and temperature of the deposits.
Because the exact ratio between water ice and dust is un-
known (15), and because the thermal gradient between the
surface and the base of the SPLD is poorly constrained (22),
we explored the range of plausible values for such parameters
and computed the corresponding range of permittivity val-
ues. The following general assumptions were made: (i) The
SPLD is composed of a mixture of water ice and dust in var-
ying proportions (from 2 to 20%), and (ii) the temperature
profile inside the SPLD is linear, starting from a fixed tem-
perature at the surface (160 K) and rising to a variable tem-
perature at the base of the SPLD (range, 170 to 270 K).
Various electromagnetic scenarios were computed (5) by con-
sidering a plane wave impinging normally onto a structure
with three layers: a semi-infinite layer with the permittivity
of free space, a homogeneous layer representing the SPLD,
and another semi-infinite layer representing the material be-
neath the SPLD, with variable permittivity values. The output
of this computation is an envelope encompassing a family of
curves that relate the normalized basal echo power to the per-
mittivity of the basal material (Fig. 4A). This envelope is used
to determine the distribution of the basal permittivity (inside
and outside the bright area) by weighting each admissible
value of the permittivity with the values of the probability
distribution of the normalized basal echo power (Fig. 4B).
This procedure generated two distinct distributions of the ba-
sal permittivity estimated inside and outside the bright re-
flection area (Fig. 4C and fig. S4), whose median values at 3,
4, and 5 MHz are 30 ± 3, 33 ± 1, and 22 ± 1 and 9.9 ± 0.5, 7.5
± 0.1, and 6.7 ± 0.1, respectively. The basal permittivity out-
side the bright area is in the range of 4 to 15, typical for dry
terrestrial volcanic rocks. It is also in agreement with previ-
ous estimates of 7.5 to 8.5 for the material at the base of the
SPLD (23) and with values derived from radar surface echo
power for dense dry igneous rocks on the martian surface at
midlatitudes (24, 25). Conversely, permittivity values as high
as those found within the bright area have not previously
been observed on Mars. On Earth, values greater than 15 are
seldom associated with dry materials (26). RES data collected
in Antarctica (27) and Greenland (9) show that a permittivity
larger than 15 is indicative of the presence of liquid water be-
low polar deposits. On the basis of the evident analogy of the
physical phenomena on Earth and Mars, we can infer that
the high permittivity values retrieved for the bright area be-
low the SPLD are due to (partially) water-saturated materials
and/or layers of liquid water.
We examined other possible explanations for the bright
area below the SPLD (supplementary text). For example, a
CO2 ice layer at the top or the bottom of the SPLD, or a very
low temperature of the H2O ice throughout the SPLD, could
enhance basal echo power compared with surface reflections.
We reject these explanations (supplementary text), either be-
cause of the very specific and unlikely physical conditions re-
quired, or because they do not cause sufficiently strong basal
reflections (figs. S5 and S6). Although the pressure and the
temperature at the base of the SPLD would be compatible
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with the presence of liquid CO2, its relative dielectric permit-
tivity is much lower (about 1.6) (28) than that of liquid water
(about 80), so it does not produce bright reflections.
The substantial amounts of magnesium, calcium, and so-
dium perchlorate in the soil of the northern plains of Mars,
discovered using the Phoenix lander’s Wet Chemistry Lab
(29), support the presence of liquid water at the base of the
polar deposits. Perchlorates can form through different phys-
ical and/or chemical mechanisms (30, 31) and have been de-
tected in different areas of Mars. It is therefore reasonable to
assume that they are also present at the base of the SPLD.
Because the temperature at the base of the polar deposits is
estimated to be around 205 K (32), and because perchlorates
strongly suppress the freezing point of water (to a minimum
of 204 and 198 K for magnesium and calcium perchlorates,
respectively) (29), we therefore find it plausible that a layer
of perchlorate brine could be present at the base of the polar
deposits. The brine could be mixed with basal soils to form a
sludge or could lie on top of the basal material to form local-
ized brine pools (32).
The lack of previous radar detections of subglacial liquid
water has been used to support the hypothesis that the polar
caps are too thin for basal melting and has led some authors
to state that liquid water may be located deeper than previ-
ously thought [e.g., (33)]. The MARSIS data show that liquid
water can be stable below the SPLD at relatively shallow
depths (about 1.5 km), thus constraining models of Mars’ hy-
drosphere. The limited raw-data coverage of the SPLD (a few
percent of the area of Planum Australe) and the large size
required for a meltwater patch to be detectable by MARSIS
(several kilometers in diameter and several tens of centime-
ters in thickness) limit the possibility of identifying small
bodies of liquid water or the existence of any hydraulic con-
nection between them. Because of this, there is no reason to
conclude that the presence of subsurface water on Mars is
limited to a single location.
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ACKNOWLEDGMENTS
We gratefully acknowledge the work of Giovanni Picardi (1936–2015), who served as
Principal Investigator of MARSIS. The MARSIS instrument and experiment were
funded by the Italian Space Agency and NASA and developed by the University of
Rome, Italy, in partnership with NASA's Jet Propulsion Laboratory (JPL),
Pasadena, CA. Alenia Spazio (now Thales Alenia Space, Italy) provided the
instrument's digital processing system and integrated the parts and now
operates the instrument and experiment. The University of Iowa, Iowa City, IA,
built the transmitter for the instrument; JPL built the receiver; and Astro
Aerospace, Carpinteria, CA, built the antenna. This research has made use of
NASA’s Astrophysics Data System. The perceptually uniform color map “broc”
was used in this study to prevent visual distortion of the data. We thank M.
Mastrogiuseppe and G. Vannaroni for insightful discussions. We are grateful to
S. E. Beaubien for careful proofreading of the manuscript and improvement of
the English. Funding: This work was supported by the Italian Space Agency (ASI)
through contract I/032/12/1. M.P. acknowledges the support from the NASA
Postdoctoral Program (2015–2017) at the Ames Research Center in Moffett
Field, California. Author contributions: R.O. devised the data calibration
method, produced maps of subsurface reflectors, developed the
electromagnetic propagation model, codeveloped the method for data
interpretation, and cowrote the paper. S.E.L. contributed to the development of
the electromagnetic propagation model, codeveloped the method for data
interpretation, and cowrote the paper. E.P. coordinated the writing of the paper,
contributed to data analysis interpretation, and discussed ideas. A.C. planned
and conducted the search for bright subsurface radar reflectors using raw data.
M.Co., B.C., F.D.P., E.F., E.M., and M.P. contributed text and figures to the
manuscript and discussed ideas. F.S. contributed to the forward and inverse
modeling of the electromagnetic propagation and scattering and discussed
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ideas. M.Ca., F.C., A.F., S.G., R.M., A.M., G.M., C.N., R.N., M.R., and R.S.
contributed to data acquisition and analysis and discussed ideas. Competing
interests: The authors declare no competing interests. Data and materials
availability: Data reported in this paper, scripts used to model electromagnetic
propagation, and the output of those scripts are available through the Zenodo
research data repository (35).
SUPPLEMENTARY MATERIALS
www.sciencemag.org/cgi/content/full/science.aar7268/DC1
Materials and Methods
Supplementary Text
Figs. S1 to S6
Table S1
References (36–53)
13 December 2017; accepted 20 June 2018
Published online 25 July 2018
10.1126/science.aar7268
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Fig. 1. Maps of the investigated area. (A) Shaded relief map of Planum Australe, Mars, south of 75°S
latitude. The map was produced using the MOLA topographic dataset (11). The black square outlines the
study area. (B) Mosaic produced using infrared observations by the THEMIS (Thermal Emission Imaging
System) camera (13), corresponding to the black square in (A). South is up in the image. The red line marks
the ground track of orbit 10737, corresponding to the radargram shown in Fig. 2A. The area consists mostly
of featureless plains, except for a few large asymmetric polar scarps near the bottom right of (B), which
suggest an outward sliding of the polar deposits (34).
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Fig. 2. Radar data collected by MARSIS. (A) Radargram for MARSIS orbit 10737, whose
ground track is shown in Fig. 1B. A radargram is a bi-dimensional color-coded section made
of a sequence of echoes in which the horizontal axis is the distance along the ground track of
the spacecraft, the vertical axis represents the two-way travel time of the echo (from a
reference altitude of 25 km above the reference datum), and brightness is a function of echo
power. The continuous bright line in the topmost part of the radargram is the echo from the
surface interface, whereas the bottom reflector at about 160 μs corresponds to the
SPLD/basal material interface. Strong basal reflections can be seen at some locations,
where the basal interface is also planar and parallel to the surface. (B) Plot of surface and
basal echo power for the radargram in (A). Red dots, surface echo power; blue dots,
subsurface echo power. The horizontal scale is along-track distance, as in (A), and the
vertical scale is uncalibrated power in decibels. The basal echo between 45 and 65 km along-
track is stronger than the surface echo even after attenuation within the SPLD.
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Fig. 3. Maps of basal topography and reflected echo power. (A) Color-coded map of the topography
at the base of the SPLD, computed with respect to the reference datum. The black contour outlines the
area in which bright basal reflections are concentrated. (B) Color-coded map of normalized basal echo
power at 4 MHz. The large blue area (positive values of the normalized basal echo power) outlined in
black corresponds to the main bright area; the map also shows other, smaller bright spots that have a
limited number of overlapping profiles. Both panels are superimposed on the infrared image shown in
Fig. 1B, and the value at each point is the median of all radar footprints crossing that point.
Fig. 4. Results of the simulation and retrieved permittivities. (A) Output of the electromagnetic simulations
computed at 4 MHz (figs. S4 and S6). The blue shaded area is the envelope of all curves incorporating different
amounts of H2O ice and dust along with various basal temperatures for the SPLD. The blue line is the curve for
a single model (basal temperature of 205 K and 10% dust content), shown for illustration, and the black
horizontal line is the median normalized basal echo power at 4 MHz from the observations. (B) Normalized basal
echo power distributions inside (blue) and outside (brown) the bright reflection area, indicating two distinct
populations of values. These distributions, together with the chart in (A), are used to compute the basal
permittivity; for example, the intersection between the blue curve and the black line gives a basal permittivity
value of 24. (C) Basal permittivity distributions inside (blue) and outside (brown) the bright reflection area. The
nonlinear relationship between the normalized basal echo power and the permittivity produces an asymmetry
(skewness) in the distributions of the values.
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