516 research outputs found
New insights on Saturn's formation from its nitrogen isotopic composition
The recent derivation of a lower limit for the N/N ratio in
Saturn's ammonia, which is found to be consistent with the Jovian value,
prompted us to revise models of Saturn's formation using as constraints the
supersolar abundances of heavy elements measured in its atmosphere. Here we
find that it is possible to account for both Saturn's chemical and isotopic
compositions if one assumes the formation of its building blocks at 45 K
in the protosolar nebula, provided that the O abundance was 2.6 times
protosolar in its feeding zone. To do so, we used a statistical thermodynamic
model to investigate the composition of the clathrate phase that formed during
the cooling of the protosolar nebula and from which the building blocks of
Saturn were agglomerated. We find that Saturn's O/H is at least 34.9
times protosolar and that the corresponding mass of heavy elements (43.1
\Mearth) is within the range predicted by semi-convective interior models.Comment: Accepted for publication in Astrophysical Journal Letter
Perchlorate formation on Mars through surface radiolysis‐initiated atmospheric chemistry: A potential mechanism
Recent observations of the Martian surface by the Phoenix lander and the Sample Analysis at Mars indicate the presence of perchlorate (ClO4–). The abundance and isotopic composition of these perchlorates suggest that the mechanisms responsible for their formation in the Martian environment may be unique in our solar system. With this in mind, we propose a potential mechanism for the production of Martian perchlorate: the radiolysis of the Martian surface by galactic cosmic rays, followed by the sublimation of chlorine oxides into the atmosphere and their subsequent synthesis to form perchloric acid (HClO4) in the atmosphere, and the surface deposition and subsequent mineralization of HClO4 in the regolith to form surface perchlorates. To evaluate the viability of this mechanism, we employ a one‐dimensional chemical model, examining chlorine chemistry in the context of Martian atmospheric chemistry. Considering the chlorine oxide, OClO, we find that an OClO flux as low as 3.2 × 107 molecules cm–2 s–1 sublimated into the atmosphere from the surface could produce sufficient HClO4 to explain the perchlorate concentration on Mars, assuming an accumulation depth of 30 cm and integrated over the Amazonian period. Radiolysis provides an efficient pathway for the oxidation of chlorine, bypassing the efficient Cl/HCl recycling mechanism that characterizes HClO4 formation mechanisms proposed for the Earth but not Mars.Key PointsMechanism initiated by radiolysis in the surface can potentially account for observed Martian perchlorate concentrationsInjection of oxides of chlorine from the surface into the atmosphere is potentially an effective way of forming perchloric acidMartian perchlorate is an important oxidant but poorly characterizedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134196/1/jgre20553.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134196/2/jgre20553_am.pd
French Meteor Network for High Precision Orbits of Meteoroids
There is a lack of precise meteoroids orbit from video observations as most of the meteor stations use off-the-shelf CCD cameras. Few meteoroids orbit with precise semi-major axis are available using film photographic method. Precise orbits are necessary to compute the dust flux in the Earth s vicinity, and to estimate the ejection time of the meteoroids accurately by comparing them with the theoretical evolution model. We investigate the use of large CCD sensors to observe multi-station meteors and to compute precise orbit of these meteoroids. An ideal spatial and temporal resolution to get an accuracy to those similar of photographic plates are discussed. Various problems faced due to the use of large CCD, such as increasing the spatial and the temporal resolution at the same time and computational problems in finding the meteor position are illustrated
Scientific Value of a Saturn Atmospheric Probe Mission
Atmospheric entry probe mISSions to the giant planets can uniquely discriminate between competing theories of solar system formation and the origin and evolution of the giant planets and their atmospheres. This provides for important comparative studies of the gas and ice giants, and to provide a laboratory for studying the atmospheric chemistries, dynamics, and interiors of all the planets including Earth. The giant planets also represent a valuable link to extrasolar planetary systems. As outlined in the recent Planetary Decadal Survey, a Saturn Probe mission - with a shallow probe - ranks as a high priority for a New Frontiers class mission [1]
Recommended from our members
Scientific rationale of a Saturn probe mission
We describe the main scientific goals to be addressed by future in situ exploration of Saturn
Two-year observations of the Jupiter polar regions by JIRAM on board Juno
We observed the evolution of Jupiter's polar cyclonic structures over two years between February 2017 and February 2019, using polar observations by the Jovian InfraRed Auroral Mapper, JIRAM, on the Juno mission. Images and spectra were collected by the instrument in the 5‐μm wavelength range. The images were used to monitor the development of the cyclonic and anticyclonic structures at latitudes higher than 80° both in the northern and the southern hemispheres. Spectroscopic measurements were then used to monitor the abundances of the minor atmospheric constituents water vapor, ammonia, phosphine and germane in the polar regions, where the atmospheric optical depth is less than 1. Finally, we performed a comparative analysis with oceanic cyclones on Earth in an attempt to explain the spectral characteristics of the cyclonic structures we observe in Jupiter's polar atmosphere
Coupled Clouds and Chemistry of the Giant Planets— A Case for Multiprobes
In seeking to understand the formation of the giant planets and the origin of their atmospheres, the heavy element abundance in well-mixed atmosphere is key. However, clouds come in the way. Thus, composition and condensation are intimately intertwined with the mystery of planetary formation and atmospheric origin. Clouds also provide important clues to dynamical processes in the atmosphere. In this chapter we discuss the thermochemical processes that determine the composition, structure, and characteristics of the Jovian clouds. We also discuss the significance of clouds in the big picture of the formation of giant planets and their atmospheres. We recommend multiprobes at all four giant planets in order to break new ground.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43766/1/11214_2005_Article_1951.pd
A primordial origin for the atmospheric methane of Saturn's moon Titan
The origin of Titan's atmospheric methane is a key issue for understanding
the origin of the Saturnian satellite system. It has been proposed that
serpentinization reactions in Titan's interior could lead to the formation of
the observed methane. Meanwhile, alternative scenarios suggest that methane was
incorporated in Titan's planetesimals before its formation. Here, we point out
that serpentinization reactions in Titan's interior are not able to reproduce
the deuterium over hydrogen (D/H) ratio observed at present in methane in its
atmosphere, and would require a maximum D/H ratio in Titan's water ice 30%
lower than the value likely acquired by the satellite during its formation,
based on Cassini observations at Enceladus. Alternatively, production of
methane in Titan's interior via radiolytic reactions with water can be
envisaged but the associated production rates remain uncertain. On the other
hand, a mechanism that easily explains the presence of large amounts of methane
trapped in Titan in a way consistent with its measured atmospheric D/H ratio is
its direct capture in the satellite's planetesimals at the time of their
formation in the solar nebula. In this case, the mass of methane trapped in
Titan's interior can be up to 1,300 times the current mass of atmospheric
methane.Comment: Accepted for publication in Icaru
The Deep Water Abundance on Jupiter: New Constraints from Thermochemical Kinetics and Diffusion Modeling
We have developed a one-dimensional thermochemical kinetics and diffusion
model for Jupiter's atmosphere that accurately describes the transition from
the thermochemical regime in the deep troposphere (where chemical equilibrium
is established) to the quenched regime in the upper troposphere (where chemical
equilibrium is disrupted). The model is used to calculate chemical abundances
of tropospheric constituents and to identify important chemical pathways for
CO-CH4 interconversion in hydrogen-dominated atmospheres. In particular, the
observed mole fraction and chemical behavior of CO is used to indirectly
constrain the Jovian water inventory. Our model can reproduce the observed
tropospheric CO abundance provided that the water mole fraction lies in the
range (0.25-6.0) x 10^-3 in Jupiter's deep troposphere, corresponding to an
enrichment of 0.3 to 7.3 times the protosolar abundance (assumed to be H2O/H2 =
9.61 x 10^-4). Our results suggest that Jupiter's oxygen enrichment is roughly
similar to that for carbon, nitrogen, and other heavy elements, and we conclude
that formation scenarios that require very large (>8 times solar) enrichments
in water can be ruled out. We also evaluate and refine the simple time-constant
arguments currently used to predict the quenched CO abundance on Jupiter, other
giant planets, and brown dwarfs.Comment: 42 pages, 7 figures, 4 tables, with note added in proof. Accepted for
publication in Icarus [in press
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