This summary analyzes observations from the Keck II telescope that detected varying amounts of hydrogen peroxide on Europa's surface. Observations over four nights found comparable amounts (~0.13%) of H2O2 on the leading hemisphere, lower amounts (~0.04%) on the anti-Jovian and sub-Jovian hemispheres, and almost none on the trailing hemisphere. This suggests the maximum concentration is found on the leading side, with lower amounts elsewhere, requiring revisions to estimates of Europa's total oxidant abundance and delivery to its subsurface ocean.
Natural Radioactivity Measurements of Basalt Rocks in Aden governorate, South...IOSR Journals
The amounts of radioactivity in the igneous rocks have been investigated; 63 basalt rock samples were collected from Aden governorate, South of Yemen. The activity concentration of 226Ra, 232Th and 40K were measured using NaI (TI) detector. Along the study area the radium equivalent activities Raeq in Bq/Kg of samples under investigation were found in the range of 51.60to 809.26Bq/Kg with an average value of 237.01Bq/Kg, this value is below the internationally accepted value of 370 Bq/Kg. To estimate the health effects of this natural radioactive composition, the average values of absorbed gamma dose rate D (55 nGyh-1), Indoor and outdoor annual effective dose rates Eied (0.11 mSvy-1), and Eoed (0.03 mSvy-1), External hazard index Hex(0.138) and internal hazard index Hin (0.154), and representative level index Iγr(0.386) have been calculated and found to be higher than the worldwide average values.
Deep Penetration Radar: Hydrogeology and Paleorelief of Underlying MediumLeonid Krinitsky
We discuss geophysical applications of enhanced-power ground penetrating radar. Its technical characteristics assure penetration depth and resolution sufficient for probing weak subsurface boundaries, such as buried riverbeds or interfaces between natural and artificial grounds. Examples of deep GPR scans demonstrate weak protracted echo signals originated at smooth permittivity gradients of the subsurface medium. Their quantitative interpretation can be done with the help of time-domain version of coupled WKB approximation.
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.
Observed glacier and volatile distribution on Pluto from atmosphere–topograph...Sérgio Sacani
Pluto has a variety of surface frosts and landforms as well as a
complex atmosphere1. There is ongoing geological activity related
to the massive Sputnik Planum glacier, mostly made of nitrogen (N2)
ice mixed with solid carbon monoxide and methane2, covering the
4-kilometre-deep, 1,000-kilometre-wide basin of Sputnik Planum1,3
near the anti-Charon point. The glacier has been suggested to arise
from a source region connected to the deep interior, or from a sink
collecting the volatiles released planetwide1. Thin deposits of N2
frost, however, were also detected at mid-northern latitudes and
methane ice was observed to cover most of Pluto except for the
darker, frost-free equatorial regions2. Here we report numerical
simulations of the evolution of N2, methane and carbon monoxide
on Pluto over thousands of years. The model predicts N2 ice
accumulation in the deepest low-latitude basin and the threefold
increase in atmospheric pressure that has been observed to occur
since 19884–6. This points to atmospheric–topographic processes as
the origin of Sputnik Planum’s N2 glacier. The same simulations also
reproduce the observed quantities of volatiles in the atmosphere and
show frosts of methane, and sometimes N2, that seasonally cover the
mid- and high latitudes, explaining the bright northern polar cap
reported in the 1990s7,8 and the observed ice distribution in 20152.
The model also predicts that most of these seasonal frosts should
disappear in the next decade.
Earth's atmosphere is a cocktail of many types of ions. These ions not only have a significant importance to mankind (for transmission of radio signals) but also are the cause of one of the most beautiful natural phenomena of aurora and airglow. Here we shall see the actual science behind the the presence of these ions in atmosphere and how they result in different phenomenon.
Natural Radioactivity Measurements of Basalt Rocks in Aden governorate, South...IOSR Journals
The amounts of radioactivity in the igneous rocks have been investigated; 63 basalt rock samples were collected from Aden governorate, South of Yemen. The activity concentration of 226Ra, 232Th and 40K were measured using NaI (TI) detector. Along the study area the radium equivalent activities Raeq in Bq/Kg of samples under investigation were found in the range of 51.60to 809.26Bq/Kg with an average value of 237.01Bq/Kg, this value is below the internationally accepted value of 370 Bq/Kg. To estimate the health effects of this natural radioactive composition, the average values of absorbed gamma dose rate D (55 nGyh-1), Indoor and outdoor annual effective dose rates Eied (0.11 mSvy-1), and Eoed (0.03 mSvy-1), External hazard index Hex(0.138) and internal hazard index Hin (0.154), and representative level index Iγr(0.386) have been calculated and found to be higher than the worldwide average values.
Deep Penetration Radar: Hydrogeology and Paleorelief of Underlying MediumLeonid Krinitsky
We discuss geophysical applications of enhanced-power ground penetrating radar. Its technical characteristics assure penetration depth and resolution sufficient for probing weak subsurface boundaries, such as buried riverbeds or interfaces between natural and artificial grounds. Examples of deep GPR scans demonstrate weak protracted echo signals originated at smooth permittivity gradients of the subsurface medium. Their quantitative interpretation can be done with the help of time-domain version of coupled WKB approximation.
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.
Observed glacier and volatile distribution on Pluto from atmosphere–topograph...Sérgio Sacani
Pluto has a variety of surface frosts and landforms as well as a
complex atmosphere1. There is ongoing geological activity related
to the massive Sputnik Planum glacier, mostly made of nitrogen (N2)
ice mixed with solid carbon monoxide and methane2, covering the
4-kilometre-deep, 1,000-kilometre-wide basin of Sputnik Planum1,3
near the anti-Charon point. The glacier has been suggested to arise
from a source region connected to the deep interior, or from a sink
collecting the volatiles released planetwide1. Thin deposits of N2
frost, however, were also detected at mid-northern latitudes and
methane ice was observed to cover most of Pluto except for the
darker, frost-free equatorial regions2. Here we report numerical
simulations of the evolution of N2, methane and carbon monoxide
on Pluto over thousands of years. The model predicts N2 ice
accumulation in the deepest low-latitude basin and the threefold
increase in atmospheric pressure that has been observed to occur
since 19884–6. This points to atmospheric–topographic processes as
the origin of Sputnik Planum’s N2 glacier. The same simulations also
reproduce the observed quantities of volatiles in the atmosphere and
show frosts of methane, and sometimes N2, that seasonally cover the
mid- and high latitudes, explaining the bright northern polar cap
reported in the 1990s7,8 and the observed ice distribution in 20152.
The model also predicts that most of these seasonal frosts should
disappear in the next decade.
Earth's atmosphere is a cocktail of many types of ions. These ions not only have a significant importance to mankind (for transmission of radio signals) but also are the cause of one of the most beautiful natural phenomena of aurora and airglow. Here we shall see the actual science behind the the presence of these ions in atmosphere and how they result in different phenomenon.
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.
Retrieval & monitoring of atmospheric green house gases (gh gs) through remot...debasishagri
Climate change is one of the most important global environmental challenges of this century. Green House Gases (GHGs) are the main culprit for this problem. Though much of research has already been done about the distribution and sources (and sinks) of GHGs , still much more uncertainties are present. Currently, there are only a few satellite instruments in orbit which are able to measure atmospheric GHGs. The High Resolution Infrared Radiation Sounder (HIRS), the Atmospheric InfraRed Sounder (AIRS), and the Infrared Atmospheric Sounding Interferometer (IASI) perform measurements in the thermal infrared (TIR) spectral region. But these are having low sensitivity to lower troposphere. In contrast to this, the sensitivity of instruments measuring reflected solar radiation in the near-infrared (NIR)/shortwave infrared (SWIR) spectral region is much more constant (with height) and shows maximum values near the surface. At present, SCIAMACHY aboard ENVISAT launched in 2002 and TANSO (Thermal And Near infrared Sensor for carbon Observation) aboard GOSAT (Greenhouse gases Observing SATellite) launched in 2009 are the only orbiting instruments measuring in NIR region. Among all the algorithms the WFM-DOAS algorithm (Weighting Function Modified Differential Optical Absorption Spectroscopy) developed at the University of Bremen for the retrieval of trace gases from SCIAMACHY (Buchwitz et al.2005) is mostly used. This is based on the principle of differential detection of radiance in gaseous absorption channels with respect to neighboring atmospheric transparent spectral channels (not influenced by gas) to detect the conc. of desired gas. But scattering at aerosol and/or cloud particles remains a major source of uncertainty for SCIAMACHY XCO2 retrievals(Houweling 2005, Schneising 2008).Of late with the use of new merged fit window approach scientists have come up with less than 0.5 ppm error in the estimation of CO2 in the presence of thin cirrus cloud(Reuter, Buchwitz et. al. 2010). Schneising et. al.,2007,retrieved d three year’s column-averaged CO2 dry air mole fraction from the SCIAMACHY instrument using the retrieval algorithm WFM-DOAS version 1.0, with precision of about 2 ppm. In India a study was undertaken to compare the atmospheric methane concentration pattern from SCIAMACHY with the vegetation dynamics from SPOT, showed fairly good correlation of methane emission with the rice cultivation(Goroshi et. al.).
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
MODELLING AND ATMOSPHERIC ERRORS IN GPS SIGNAL PROPAGATIONSHADABANSARI57
A BRIEF INTRODUCTION TO IONOSPHERIC AND TROPOSPHERIC ERRORS IN GPS SIGNAL PROPAGATION
DERIVATION OF FORMULA WITH THE BASIC LEVEL.
BASIC UNDERSTANDING OF FIGURE..
FOLLOW THE REFERENCE BOOK FOR MORE DETAIL.
First results from_the_hubble_opal_program_jupiter_in_2015Sérgio Sacani
Os cientistas usando o Telescópio Espacial Hubble da NASA/ESA produziram novos mapas de Júpiter, que mostram as contínuas mudanças que ocorrem com a famosa Grande Mancha Vermelha. As imagens também revelam uma rara estrutura em forma de onda na atmosfera do planeta que não tinha sido vista por décadas. A nova imagem é a primeira de uma série de retratos anuais dos planetas externos do Sistema Solar, que nos darão um novo olhar desses mundos remotos, e ajudarão os cientistas a estudarem como eles mudam com o passar do tempo.
Nessa nova imagem de Júpiter, uma grande quantidade de feições foi capturada incluindo ventos, nuvens e tempestades. Os cientistas por trás dessas novas imagens, as obtiveram usando a Wide Field Camera 3 do Hubble, num período de observação de mais de 10 horas e produziram assim dois mapas completos do planeta, a partir das suas observações. Esses mapas fizeram com que fosse possível determinar a velocidade dos ventos em Júpiter, com a finalidade de identificar diferentes fenômenos na sua atmosfera além de traquear as suas feições mais famosas.
As novas imagens confirmam que a grande tempestade que tem existido na superfície de nuvens de Júpiter por no mínimo 300 anos, continua a encolher, mas mesmo que desapareça, ela irá morrer lutando. A tempestade, conhecida como Grande Mancha Vermelha, é vista aqui fazendo seus movimentos em espiral no centro da imagem do planeta. Ela tem diminuído de tamanho de maneira muito rápida de ano em ano. Mas agora, a taxa de encolhimento parece ter reduzido novamente, mesmo apesar da mancha ser cerca de 240 quilômetros menor do que era em 2014.
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
07 April Giovanni Nico: Application seminar: high resolution weather maps
An applicative seminar on augmenting meteorological analysis with remote sensing observations
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.
Retrieval & monitoring of atmospheric green house gases (gh gs) through remot...debasishagri
Climate change is one of the most important global environmental challenges of this century. Green House Gases (GHGs) are the main culprit for this problem. Though much of research has already been done about the distribution and sources (and sinks) of GHGs , still much more uncertainties are present. Currently, there are only a few satellite instruments in orbit which are able to measure atmospheric GHGs. The High Resolution Infrared Radiation Sounder (HIRS), the Atmospheric InfraRed Sounder (AIRS), and the Infrared Atmospheric Sounding Interferometer (IASI) perform measurements in the thermal infrared (TIR) spectral region. But these are having low sensitivity to lower troposphere. In contrast to this, the sensitivity of instruments measuring reflected solar radiation in the near-infrared (NIR)/shortwave infrared (SWIR) spectral region is much more constant (with height) and shows maximum values near the surface. At present, SCIAMACHY aboard ENVISAT launched in 2002 and TANSO (Thermal And Near infrared Sensor for carbon Observation) aboard GOSAT (Greenhouse gases Observing SATellite) launched in 2009 are the only orbiting instruments measuring in NIR region. Among all the algorithms the WFM-DOAS algorithm (Weighting Function Modified Differential Optical Absorption Spectroscopy) developed at the University of Bremen for the retrieval of trace gases from SCIAMACHY (Buchwitz et al.2005) is mostly used. This is based on the principle of differential detection of radiance in gaseous absorption channels with respect to neighboring atmospheric transparent spectral channels (not influenced by gas) to detect the conc. of desired gas. But scattering at aerosol and/or cloud particles remains a major source of uncertainty for SCIAMACHY XCO2 retrievals(Houweling 2005, Schneising 2008).Of late with the use of new merged fit window approach scientists have come up with less than 0.5 ppm error in the estimation of CO2 in the presence of thin cirrus cloud(Reuter, Buchwitz et. al. 2010). Schneising et. al.,2007,retrieved d three year’s column-averaged CO2 dry air mole fraction from the SCIAMACHY instrument using the retrieval algorithm WFM-DOAS version 1.0, with precision of about 2 ppm. In India a study was undertaken to compare the atmospheric methane concentration pattern from SCIAMACHY with the vegetation dynamics from SPOT, showed fairly good correlation of methane emission with the rice cultivation(Goroshi et. al.).
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
MODELLING AND ATMOSPHERIC ERRORS IN GPS SIGNAL PROPAGATIONSHADABANSARI57
A BRIEF INTRODUCTION TO IONOSPHERIC AND TROPOSPHERIC ERRORS IN GPS SIGNAL PROPAGATION
DERIVATION OF FORMULA WITH THE BASIC LEVEL.
BASIC UNDERSTANDING OF FIGURE..
FOLLOW THE REFERENCE BOOK FOR MORE DETAIL.
First results from_the_hubble_opal_program_jupiter_in_2015Sérgio Sacani
Os cientistas usando o Telescópio Espacial Hubble da NASA/ESA produziram novos mapas de Júpiter, que mostram as contínuas mudanças que ocorrem com a famosa Grande Mancha Vermelha. As imagens também revelam uma rara estrutura em forma de onda na atmosfera do planeta que não tinha sido vista por décadas. A nova imagem é a primeira de uma série de retratos anuais dos planetas externos do Sistema Solar, que nos darão um novo olhar desses mundos remotos, e ajudarão os cientistas a estudarem como eles mudam com o passar do tempo.
Nessa nova imagem de Júpiter, uma grande quantidade de feições foi capturada incluindo ventos, nuvens e tempestades. Os cientistas por trás dessas novas imagens, as obtiveram usando a Wide Field Camera 3 do Hubble, num período de observação de mais de 10 horas e produziram assim dois mapas completos do planeta, a partir das suas observações. Esses mapas fizeram com que fosse possível determinar a velocidade dos ventos em Júpiter, com a finalidade de identificar diferentes fenômenos na sua atmosfera além de traquear as suas feições mais famosas.
As novas imagens confirmam que a grande tempestade que tem existido na superfície de nuvens de Júpiter por no mínimo 300 anos, continua a encolher, mas mesmo que desapareça, ela irá morrer lutando. A tempestade, conhecida como Grande Mancha Vermelha, é vista aqui fazendo seus movimentos em espiral no centro da imagem do planeta. Ela tem diminuído de tamanho de maneira muito rápida de ano em ano. Mas agora, a taxa de encolhimento parece ter reduzido novamente, mesmo apesar da mancha ser cerca de 240 quilômetros menor do que era em 2014.
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
07 April Giovanni Nico: Application seminar: high resolution weather maps
An applicative seminar on augmenting meteorological analysis with remote sensing observations
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
Measurement of lmpulsive Thrust from a Closed Radio Frequency Cavity in VacuumSérgio Sacani
A vacuum test campaign evaluating the impulsive thrust performance of a tapered RF test article excited in the TM212 mode at 1,937 megahertz (MHz) has been completed. The test campaign consisted of a forward thrust phase and reverse thrust phase at less than 8 x 10-6 Torr vacuum with power scans at 40 watts, 60 watts, and 80 watts. The test campaign included a null thrust test effort to identify any mundane sources of impulsive thrust, however none were identified. Thrust data from forward, reverse, and null suggests that the system is consistently performing with a thrust to power ratio of 1.2 ± 0.1 mN/kW.
The extremely high albedo of LTT 9779 b revealed by CHEOPSSérgio Sacani
Optical secondary eclipse measurements of small planets can provide a wealth of information about the reflective properties
of these worlds, but the measurements are particularly challenging to attain because of their relatively shallow depth. If such signals
can be detected and modeled, however, they can provide planetary albedos, thermal characteristics, and information on absorbers in
the upper atmosphere.
Aims. We aim to detect and characterize the optical secondary eclipse of the planet LTT 9779 b using the CHaracterising ExOPlanet
Satellite (CHEOPS) to measure the planetary albedo and search for the signature of atmospheric condensates.
Methods. We observed ten secondary eclipses of the planet with CHEOPS. We carefully analyzed and detrended the light curves using
three independent methods to perform the final astrophysical detrending and eclipse model fitting of the individual and combined light
curves.
Results. Each of our analysis methods yielded statistically similar results, providing a robust detection of the eclipse of LTT 9779 b
with a depth of 115±24 ppm. This surprisingly large depth provides a geometric albedo for the planet of 0.80+0.10
−0.17, consistent with
estimates of radiative-convective models. This value is similar to that of Venus in our own Solar System. When combining the eclipse
from CHEOPS with the measurements from TESS and Spitzer, our global climate models indicate that LTT 9779 b likely has a super
metal-rich atmosphere, with a lower limit of 400× solar being found, and the presence of silicate clouds. The observations also reveal
hints of optical eclipse depth variability, but these have yet to be confirmed.
Conclusions. The results found here in the optical when combined with those in the near-infrared provide the first steps toward
understanding the atmospheric structure and physical processes of ultrahot Neptune worlds that inhabit the Neptune desert.
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.
The shape radio_signals_wavefront_encountered_in_the_context_of_the_uhecr_rad...Ahmed Ammar Rebai PhD
"Uploaded only for Authors copyrights 9/9/2014. All rights reserved"
Ultra high energy cosmic rays are the most extreme energetic subatomic particles
in nature. Coming from the outer space, these particles initiate extensive air showers (EAS) in
the Earth’s atmosphere. The generated EAS produce elusive radio-transients in the MHz frequency
band measured by sensitive antenna arrays and radio telescopes. Theoretical developments indicate
that the EAS radio wavefront shape depends on the shower longitudinal development, it is waited
that the wavefront curved shape provides information to answer many fundamental questions about
UHECR nature and origins. In the first part of this paper, we report on an investigation in the
wavefront shape, based on an already published sample of events collected between November
2006 and January 2010 at the CODALEMA II experiment located in the radioastronomy facility at
Nançay in France. We find that measurements of individual air showers have been conclusive for
a non-planar shape which could be hyperbolical (further analysis are needed). By cons and in the
second part of this paper, a spherical shape of the wavefront for the anthropic radio-sources has been
proposed. Many studies have shown the strong dependence of the solution of the radio-transient
sources localization problem (the radio wavefront time of arrival on antennas TOA), such solutions
are purely numerical artifacts. Based on a detailed analysis of some published results of radio-
detection experiments around the world like : CODALEMA III in France, AERA in Argentina,
TREND in China and LUNASKA in Australia, we demonstrate the ill-posed character of this
problem in the sense of Hadamard. To support the mathematical studies, a comparison between the
experimental results and the simulations have been made.
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.
Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydroth...Sérgio Sacani
Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from
cracks in the ice. The plume contains chemical signatures of water-rock interaction
between the ocean and a rocky core.We used the Ion Neutral Mass Spectrometer onboard
the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s
open-source mode, background processes of hydrogen production in the instrument were
minimized and quantified, enabling the identification of a statistically significant signal of
hydrogen native to Enceladus.We find that the most plausible source of this hydrogen is
ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.
The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium
that favors the formation of methane from CO2 in Enceladus’ ocean.
The pristine nature of SMSS 1605−1443 revealed by ESPRESSOSérgio Sacani
SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] =
−6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C) ≈ 6.1 in the low-C band, as the majority of the stars
in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive
stars.
Aims. We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial
velocity (vrad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The
12C/
13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion.
Methods. A cross-correlation function against a natural template was applied to detect vrad variability and a spectral synthesis technique was used
to derive 12C/
13C in the stellar atmosphere.
Results. We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/
13C > 60 at more than a 3σ confidence
level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm
the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted
in its stellar atmosphere free of contamination.
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
Um dos artigos da edição especial da revista Science, mostrando as alterações nas propriedades do cometa Churyumov-Gerasimenko, à medida que ele se aproxima do Sol.
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
X-rays from a Central “Exhaust Vent” of the Galactic Center Chimney
Keck ii observations_of_hemispherical_differences_in_h2o2_on_europa
1. Keck II Observations of Hemispherical Differences in H2 O2 on Europa
K.P. Hand
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109
arXiv:1303.5895v1 [astro-ph.EP] 23 Mar 2013
khand@jpl.nasa.gov
M.E. Brown
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA
91125
ABSTRACT
We present results from Keck II observations of Europa over four consecutive nights
using the near-infrared spectrograph (NIRSPEC). Spectra were collected in the 3.14–4.0
µm range, allowing detection and monitoring of the 3.5 µm feature due to hydrogen
peroxide. Galileo Near-Infrared Spectrometer (NIMS) results first revealed hydrogen
peroxide on Europa in the anti-jovian region of the leading hemisphere at an abundance
of 0.13±0.07% by number relative to water. We find comparable results for the two
nights over which we observed the leading hemisphere. Significantly, we observed a small
amount of hydrogen peroxide (∼0.04%) during observations of Europa’s anti- and sub-
Jovian hemispheres. Almost no hydrogen peroxide was detected during observations of
just the trailing hemisphere. We conclude that the Galileo observations likely represent
the maximum hydrogen peroxide concentration, the exception potentially being the
cold water ice regions of the poles, which are not readily observable from the ground.
Our mapping of the peroxide abundance across Europa requires revisions to previous
estimates for Europa’s global surface abundance of oxidants and leads to a reduction
in the total oxidant delivery expected for the sub-surface ocean, if exchange of surface
material with the ocean occurs.
Subject headings: infrared: planetary systems — astrochemistry — planets and satel-
lites: surfaces — planets and satellites: composition
1. Introduction
The interaction of the Jovian magnetosphere with Europa results in radiolytic processing of
the icy surface (Johnson 1990; Johnson & Quickenden 1997). Energetic electrons, ions, and protons
dissociate water, yielding OH radicals, which then can recombine forming hydrogen peroxide and
other oxidants (Cooper et al. 2003; Johnson et al. 2003).
2. –2–
Importantly, Europa is synchronously locked to Jupiter (Europa rotates on its axis once per
86 hour orbit around Jupiter), and thus Europa’s hemispheres maintain the same orientation with
respect to Jupiter and the radiation environment of the magnetosphere. Over 75% of the incident
radiation is from electrons (Cooper et al. 2001) and, due to their small gyroradii and the fast
rotation of Jupiter (10 hours) relative to Europa’s orbital period, the trailing hemisphere of Europa
receives the majority of the radiation. Furthermore, low energy sulfur ions in the plasma torus are
preferentially deposited on the trailing hemisphere. This relationship is made evident by the trailing
hemisphere ‘bulls-eye’ feature of dark material (Paranicas et al. 2001), most likely a radiolytically
processed sulfur compound such as hydrated sulfuric acid (Carlson et al. 1999b) and endogenous
magnesium ions that have been radiolytically processed to magnesium sulfate (Brown and Hand,
submitted).
Galileo Near Infrared Mapping Spectrometer (NIMS) observations of Europa first detected
hydrogen peroxide in the anti-Jovian region of the leading hemisphere at an abundance of 0.13+/-
0.07% by number relative to water (Carlson et al. 1999a). As shown by Loeffler et al. (2006),
the equilibrium peroxide concentration for ion-irradiated 80 K and 120 K ice is 0.14% and 0.1%
by number respectively. Though peroxide has been reported for other regions of Europa, those
observations were noisy and poorly quantified (Hansen & McCord 2008).
Here we present new results for measurement of the peroxide abundance across all four major
hemispheres of Europa (leading, trailing, sub-Jovian, and anti-Jovian) using ground based spec-
troscopy.
2. Observations
Observations of Europa were obtained over four consecutive nights from 17 until 20 September
2011 using NIRCSPEC, the facility near infrared spectrograph (McLean et al. 1998), on the Keck
telescope. We covered a wavelength range from 3.14 - 4.00 µm in the low resolution mode with R
∼ 2000, which is still a factor of ∼20 better than the NIMS instrument. We used the 0.76” wide
slit, such that for a given observation most of the observable hemisphere of Europa was within
the slit. At the time of our observations the 3120 km diameter of Europa subtended 1.028”, or
approximately 2300 km. While observers of the Galilean satellites often use other Galilean satellites
for telluric and solar flux correction, as they are bright and adjacent, we chose, instead, to avoid the
possibility of spectral contamination and used HD 9986, a V=6.67 G5V star that was 13 degrees
away from Europa at the time of observations. Observations on the target and calibrators were
obtained in an ABBA pattern, with a single pointing for Europa consisting of 60 2-second coadds
and for the calibrator star 10 1-second coadds. A journal of the observations is shown in Table 1.
The initial data reductions were performed using standard routines that subtract adjacent
pairs of images, correct for the curvature in the spatial and spectral dimensions, fit and subtract
residual line emission, and optimally extract the remaining spectrum. From the initial extracted
3. –3–
spectra, it was clear that the data were affected by variable water vapor absorption and by a line-
shape difference between the resolved target and the point source stellar calibrator. To correct for
these effects, we first created a grid of model telluric spectra using the online ATRAN (Lord 1992)
tool for SOFIA1 spanning a range of air masses and water vapor overburdens, convolved to the
resolution of the NIRSPEC data. We divided each stellar spectrum by the model spectra, finding
the parameters which minimized the residuals and determined the effects of slight changes in the
water vapor burden and airmass for the stellar spectra. We then performed a χ2 minimization on
the calibrated target spectra where we varied the spectral broadening of the target, the precise
wavelength offset between the calibrator and target, and the magnitude of small water vapor and
airmass corrections. For these bright sources, few atmospheric emission lines are visible in the raw
data, so wavelength calibration is performed by matching the model transmission spectra to the
uncorrected stellar spectra. The resulting spectra are generally excellent, but with clear uncorrected
water vapor residuals shortward of 3.3 µm.
3. Results
The reflectance data for each night was normalized to the maximum reflectance value for the
bright, leading hemisphere on the night of the 18th, which showed good agreement with previous
albedo measurements for Europa’s surface (Calvin et al. 1995; Grundy et al. 2007; Carlson et al.
2009).
The surface abundance of hydrogen peroxide, expressed as its percent by number abun-
dance relative to water, was determined by converting reflectance values, R, to absorbance, A =
− ln (R/RBaseline ), where the baseline reflectance used was the maximum reflectance value for the
night of the 18th, which was the spectrum representing the purest ice. We then used a second
degree least squares polynomial fit to the broad 3 µm water feature so as to enable removal of the
continuum. The peroxide band was integrated to get the total band area from 3.4 to 3.6 µm (2760
cm−1 to 2950 cm−1 ). As part of the polynomial fit we calculated the one standard deviation values
above and below the fit and then integrated the corresponding band areas to get 1 σ values for the
total absorbance.
To generate peroxide concentrations for each night of observations we used the temperature
dependent band strength values from Loeffler et al. (2006), and selected A100K = (5.0±0.5)×10−17
cm molec−1 as a reasonable value for the average hemisphere temperature of 100 K (Spencer et al.
1999). Dividing the integrated band strength by the A-value yields the total number of H2 O2
molecules, which when divided by the number of water molecules for the optical depth yields the
concentration relative to water. Following Hudgins et al. (1993) and Carlson et al. (1999a) we use
a 50 µm grain size and optical depth, and an ice density of 3×1022 molecules per square centimeter.
1
http://atran.sofia.usra.edu/cgi-bin/atran/atran.cgi
4. –4–
Figure 1 shows the averaged spectrum for each night, and shows the polynomial fit and 1 σ bounds.
The band with the continuum subtracted is shown with the Galileo NIMS data overlain (x marks).
The leading hemisphere of Europa, as determined by observations with a central Europa lon-
gitude ranging from 52◦ to 62◦ , has a 0.113 ± 0.032 (0.074-0.161) percent by number abundance
relative to water, where the range in parenthesis includes the uncertainty in the A-value. This range
is in close agreement with the NIMS observations, which had an uncertainty of ±0.07. For added
comparison we analyzed the Galileo NIMS data using the more recent band strengths (Loeffler et al.
2006) and found that the NIMS data lead to a percent by number abundance of 0.118% peroxide
relative to water. This value is slightly less than the 0.13% value reported by Carlson et al. (1999a),
but well within the published error bars for that observation, and is in very close agreement with
our observations.
The trailing hemisphere of Europa, which is dominated by a darker non-ice material, was found
to have a peroxide abundance close to or equal to zero. These observations had a central Europa
longitude ranging from 256◦ to 264◦ and thus were centered on the apex of the trailing hemisphere.
As the spectrum shows, there is only a slight rise above the continuum at 3.5 µm. The measured
concentration range is 0.0 to a maximum of 0.038 (or 0.043 for A100K = 4.5 × 10−17 cm molec−1 ,
using the low-end value for the error limits on A100K ) percent by number abundance, with our best
fit value being 0.018 for a 100 K surface.
Observations that included the sub-Jovian (Jupiter facing) and anti-Jovian hemispheres of
Europa show peroxide concentrations of approximately 1/3 that of the leading hemisphere, though
as shown in Table 1 the longitude ranges for these observations do partially overlap with the leading
and trailing hemispheres. The September 19th observations centered on a longitude of 158◦ to
161◦ , covering the leading to anti-Jovian hemispheres, and indicate a concentration of 0.045 ± 0.019
(0.023-0.072) percent by number abundance. The September 17th observations that centered on
a longitude ranging from 315◦ to 316◦ , and thus covered the trailing to sub-Jovian hemispheres,
yield a concentration of 0.042 ± 0.041 (0.0-0.092) at 100 K.
4. Discussion
Our results show a non-uniform distribution of hydrogen peroxide across the surface of Europa.
Three key factors likely control the production and abundance of peroxide on Europa’s surface:
1) the availability of water molecules, 2) radiation (UV, electrons, and ions all yield peroxide
(Johnson & Quickenden 1997; Johnson et al. 2003)), and 3) temperature (Moore & Hudson 2000;
Loeffler et al. 2006; Hand & Carlson 2011). Though the trailing hemisphere of Europa has a higher
radiation flux, it is also dominated by a strong non-ice component that limits the production and
steady-state abundance of hydrogen peroxide. Our results, coupled with water ice abundance maps
(Grundy et al. 2007; Carlson et al. 2009; Brown & Hand submitted), clearly show that peroxide
abundance maps most directly to the availability of water, which is the precursor molecule that
5. –5–
provides the OH radical upon dissociation by irradiation (Cooper et al. 2003). Though water
molecules may present as part of the hydrated sulfate that dominates the trailing hemisphere
(Carlson et al. 2009), peroxide does not appear to be a dominant product of the sulfate radiolysis.
Ice temperature significantly modulates peroxide production and stability, as the trapping of
OH and electrons in the ice matrix (Quickenden et al. 1991) decreases in efficiency over the ∼ 70-130
K temperature range of Europa’s surface (Spencer et al. 1999), leading to reduced concentrations
at higher temperature (Hand & Carlson 2011). However, variation in band absorption from 80 K
to 120 K yields a ∼10% change in concentration (Loeffler et al. 2006) and thus cannot explain the
difference in concentration across hemispheres. Interestingly, comparison with Loeffler & Baragiola
(2005) indicates that the state of peroxide on Europa is that of dispersed H2 O2 · 2H2 O trimers. In
warmer regions and on e.g. Ganymede and Callisto - where peroxide has not been observed - the
expected state of peroxide is that of the precipitated and crystallized dihydrate. Our ground based
observations agree with these lab based measurements for the state of peroxide on Europa.
Given that condensed O2 has been reported as a component in the surface ice of Europa without
longitudinal variation (Spencer & Calvin 2002), and that H2 O2 is a useful precursor molecule in
pathways to O2 production (Cooper et al. 2003), the differences in peroxide concentrations may
provide some bearing on the origin of Europa’s oxygen distribution and production pathways.
Teolis et al. (2005) note that destruction of hydrogen peroxide alone cannot explain the observed
oxygen abundance and thus other pathways are important to consider. We suggest that perhaps
Spencer & Calvin (2002) did observe longitudinal variations in O2 that could be associated with
H2 O2 as a precursor, but given the limited measurements and the sensitivity of the 5770 ˚ band,
A
they did not have sufficient evidence for such a conclusion. Indeed, close inspection of their Figure
2 reveals that the oxygen absorption on the leading hemisphere is deeper and broader than that
of the trailing hemisphere, with a band depth difference of ∼10-25%. Our measurements showing
variations in H2 O2 across Europa’s surface provide a compelling rationale for a more detailed
investigation of Europa’s O2 abundance and distribution.
Nevertheless, the Spencer & Calvin (2002) observations do show significant O2 on the trailing
hemisphere. In light of our results, we propose that O2 may be a more stable radiation product (as is
clearly the case in Earth’s atmosphere) and thus the low levels of peroxide on the trailing hemisphere
do not prohibit a measurable steady state abundance of oxygen on the trailing hemisphere. The
high abundance of sulfur on the trailing hemisphere may also serve to scavenge OH radicals to form
H2 SO4 , and SO2 may be an alternative precursor to O2 .
Additionally, oxygen can easily migrate across the surface of Europa as it transitions from solid
to gas phase with Europa’s diurnal temperature cycles (Hall et al. 1995; Cassidy et al. 2007). The
leading hemisphere may be the dominant source of O2 production in the ice, but warming releases
that oxygen to the exosphere, where it then migrates and recondenses depending on the diurnal
thermal pulse. This scenario is further aided by the fact that UV photolysis is enhanced during
the day, and photolysis of peroxide yields OH and possibly alternative pathways for O2 formation
6. –6–
(Grunewald et al. 1986; Johnson et al. 2003).
Finally, we note that the radiolytic production of surface oxidants has long been of interest in
the context of Europa’s subsurface ocean chemistry (Gaidos et al. 1999; Chyba 2000; Chyba & Hand
2001). If Europa’s oxidant laden surface ice mixes with the ocean water then radiolysis could be
a key mechanism for maintaining a chemically-rich and potentially habitable ocean (Chyba 2000;
Hand et al. 2009). Previous estimates all assumed a globally uniform layer of peroxide within the
ice layer and calculated delivery rates based the NIMS concentration of 0.13% relative to water.
Our new results indicate that only the most ice-rich regions of Europa reach the concentrations
measured by NIMS. The trailing hemisphere concentration is nearly an order of magnitude lower
than the leading hemisphere and the sub- and anti-Jovian hemispheres are down by a factor of ∼3
relative to the leading hemisphere. As a result, the average global surface abundance of peroxide
in the surface ice of Europa may be better represented by the sub- and anti-Jovian hemisphere
concentrations of ∼0.044%. This reduces the low-end estimate of Chyba & Hand (2001) from
∼ 109 moles per year peroxide delivered to the ocean to ∼ 108 moles per year delivered. Compared
to models for seafloor production of reductants, such as methane and hydrogen sulfide, which yield
∼ 3 × 109 moles per year delivered to the ocean, it appears that our new results for peroxide
on Europa could lead to an ocean limited by oxidant availability. This conclusion also depends
strongly on the global geographic distribution of O2 , which may have concentrations significantly
larger than peroxide (Hand et al. 2007).
This research has been supported by grant NNX09AB49G from the NASA Planetary Astron-
omy program and by the NASA Astrobiology Institute ’Icy Worlds’ node at JPL/Caltech. The
authors thank Robert W. Carlson for helpful discussions.
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This preprint was prepared with the AAS L TEX macros v5.2.
A
9. –9–
(a) (b)
(c) (d)
Fig. 1.— Averaged spectrum for each night (∼ 6 hrs) showing the polynomial fit (solid line through
the data) and 1 σ bounds (dashed lines). Also shown is the hydrogen peroxide band with the water
continuum subtracted and the Galileo NIMS data overlain (x marks). The diagram within each
spectrum shows a top-down view of Europa’s orbit, with Jupiter at the center and the Earth toward
the bottom of the page. The grey wedge shows the ∼25◦ region subtended by Europa as it moves
in its orbit over the 6 hour observation period for each night. L is the central Europa longitude of
the observations.
10. – 10 –
Table 1. Summary of Europa observations.
date target time airmass longitude exp. time
(UT) start/end start/end start/end (sec)
2011 Sep 17 Europa – 12:45/12:54 1.01/1.01 315/316 840
sub-Jup iter
HD 9866 13:56 1.10 40
2011 Sep 18 HD 9866 11:40 1.02 40
Europa – 11:47/13:58 1.06/1.02 52/62 6240
leading
2011 Sep 19 HD 9866 11:25 1.02
Europa – 12:50/13:20 1.01/1.01 158/161 1440
anti-Jupiter
2011 Sep 20 HD 9866 11:48 1.04 40
Europa – 11:55/13:57 1.04/1.04 256/264 5760
trailing