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  • 1
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    On the escape of CH4 from Pluto's atmosphere (2015)
    Wiley
    Details
    Publication Date: 2015-08-15
    Description: We adapted a multi-species escape model, developed for close-in extrasolar planets, to calculate the escape rates of CH 4 and N 2 from Pluto. In the absence of escape, CH 4 should overtake N 2 as the dominant species below the exobase. The CH 4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for Pluto lead to a nearly constant mixing ratio of less than 1 % below the exobase. In this case the CH 4 escape rate is only 5–10 % of the N 2 escape rate. Observations of the CH 4 profile by the New Horizons/ALICE spectrograph can constrain the CH 4 escape rate and provide a unique test for escape models.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars (2015)
    Wiley
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    Publication Date: 2015-06-18
    Description: We report the detection of intense emission from magnesium and iron in Mars' atmosphere caused by a meteor shower following Comet Siding Spring's close encounter with Mars. The observations were made with the Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars. Ionized magnesium caused the brightest emission from the planet's atmosphere for many hours, resulting from resonant scattering of solar ultraviolet light. Modeling suggests a substantial fluence of low-density dust particles 1–100 µm in size, with the large amount and small size contrary to predictions. The event created a temporary planet-wide ionospheric layer below Mars' main dayside ionosphere. The dramatic meteor shower response at Mars is starkly different from the case at Earth, where a steady state metal layer is always observable but perturbations caused by even the strongest meteor showers are challenging to detect.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Metallic ions in the upper atmosphere of Mars from the passage of comet C/2013 A1 (Siding Spring) (2015)
    Wiley
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    Publication Date: 2015-06-18
    Description: We report the first in situ detection of metal ions in the upper atmosphere of Mars resulting from the ablation of dust particles from comet Siding Spring. This detection was carried out by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution Mission. Metal ions of Na, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and possibly of Si, and Ca, were identified in the ion spectra collected at altitudes of ~185 km. The measurements revealed that Na + was the most abundant species, and that the remaining metals were depleted with respect to the CI (type 1 carbonaceous Chondrites) abundance of Na + . The temporal profile and abundance ratios of these metal ions suggest that the combined effects of dust composition, partial ablation, differential upward transport, and differences in the rates of formation and removal of these metal ions are responsible for the observed depletion.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Probing the Martian atmosphere with MAVEN/IUVS stellar occultations (2015)
    Wiley
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    Publication Date: 2015-11-06
    Description: The first campaign of stellar occultations with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board of Mars Atmosphere and Volatile EvolutioN (MAVEN) mission was executed between 24 and 26 March 2015. From this campaign 13 occultations are used to retrieve CO 2 and O 2 number densities in the altitude range between 100 and 150 km. Observations probe primarily the low-latitude regions on the nightside of the planet, just past the dawn and dusk terminator. Calculation of temperature from the CO 2 density profiles reveals that the lower thermosphere is significantly cooler than predicted by the models in the Mars Climate Database. A systematically cold layer with temperatures of 105–120 K is seen in the occultations at a pressure level around 7 × 10 −6 Pa.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    The implications of the H2 variability in Titan's exosphere (2011)
    Wiley
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    Publication Date: 2011-11-19
    Description: We present in this paper an investigation of the distribution of H2 in Titan's exosphere, based on the measurements made with the Ion Neutral Mass Spectrometer (INMS) onboard Cassini during 32 encounters with the satellite. The observed H2 density in Titan's exosphere shows significant variance from flyby to flyby. However, no appreciable trend with geophysical or solar conditions can be identified. A data-model comparison is made in the framework of the Chamberlain approach, taking into account two ideal cases. First, we assume that the observed variability is spatial. In this case, the damping of exobase perturbations when propagating into the exosphere is a diagnostic of the spatial scale of the perturbations. We find that for all reasonable choices of this spatial scale, the model predicts significantly more damping than implied by the INMS data. Second, we assume that at any given time, the physical conditions in Titan's upper atmosphere and exosphere are globally uniform, but these conditions evolve with time, indicating that the observed variability is temporal. In such a case, the observations can be interpreted as a result of exobase perturbations on timescales in the range of ∼103–106 s. The time-varying H2 exosphere of Titan essentially reflects the varying structure and energy deposition in the upper atmosphere of the satellite, which are ultimately determined by the variations in either the solar EUV/UV radiation or the level of magnetospheric particle precipitation. However, we do not expect the considerable variability observed for Titan's H2 exosphere to be induced by the varying solar inputs into Titan's atmosphere. Instead, we postulate that such a variability is more likely to be associated with Titan's varying plasma environment. Comparisons between different categories of Titan flybys tentatively reveal that the H2 exosphere tends to be more energetic and more expanded, and H2 molecules tend to escape more rapidly, with increasing levels of electron precipitation from the ambient plasma environment.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    The morphology of the topside Martian ionosphere: Implications on bulk ion flow (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Prior to the Mars Atmosphere and Volatile Evolution (MAVEN) mission, the only information on the composition of the Martian ionosphere came from the Viking Retarding Potential Analyzer data, revealing the presence of substantial ion outflow on the dayside of Mars. Extensive measurements made by the MAVEN Neutral Gas and Ion Mass Spectrometer allow us to examine the morphology of the Martian ionosphere not only in unprecedented detail but also on both the dayside and the nightside of the planet. Above 300 km, various ionospheric species present a roughly constant density scale height around 100 km on the dayside and 180 km on the nightside. An evaluation of the ion force balance, appropriate for regions with near horizontal magnetic field lines, suggests the presence of supersonic ion outflow predominantly driven by the ambient magnetic pressure, with characteristic dayside and nightside flow velocities of 4 km s−1 and 20 km s−1, respectively, both referred to an altitude of 500 km. The corresponding total ion outflow rates are estimated to be 5 × 1025 s−1 on the dayside and 1 × 1025 s−1 on the nightside. The data also indicate a prominent variation with magnetic field orientation in that the ion distribution over regions with near vertical field lines tends to be more extended on the dayside but more concentrated on the nightside, as compared to regions with near horizontal field lines. These observations should have important implications on the pattern of ion dynamics in the vicinity of Mars.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    The dusty atmosphere of the brown dwarf Gliese 229B (1998)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1998-12-16
    Description: The brown dwarf Gliese 229B has an observable atmosphere too warm to contain ice clouds like those on Jupiter and too cool to contain silicate clouds like those on low-mass stars. These unique conditions permit visibility to higher pressures than possible in cool stars or planets. Gliese 229B's 0.85- to 1.0-micrometer spectrum indicates particulates deep in the atmosphere (10 to 50 bars) having optical properties of neither ice nor silicates. Their reddish color suggests an organic composition characteristic of aerosols in planetary stratospheres. The particles' mass fraction (10(-7)) agrees with a photochemical origin caused by incident radiation from the primary star and suggests the occurrence of processes native to planetary stratospheres.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Griffith, C A -- Yelle, R V -- Marley, M S -- New York, N.Y. -- Science. 1998 Dec 11;282(5396):2063-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011-6010, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9851924" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; *Astronomy ; Atmosphere ; *Extraterrestrial Environment ; Organic Chemicals/*analysis ; Temperature ; Ultraviolet Rays
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Observations of comet 19P/Borrelly by the miniature integrated camera and spectrometer aboard Deep Space 1 (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-04-06
    Description: The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (〈/=345 kelvin, with no trace of water ice or hydrated minerals), consistent with approximately 10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Soderblom, L A -- Becker, T L -- Bennett, G -- Boice, D C -- Britt, D T -- Brown, R H -- Buratti, B J -- Isbell, C -- Giese, B -- Hare, T -- Hicks, M D -- Howington-Kraus, E -- Kirk, R L -- Lee, M -- Nelson, R M -- Oberst, J -- Owen, T C -- Rayman, M D -- Sandel, B R -- Stern, S A -- Thomas, N -- Yelle, R V -- New York, N.Y. -- Science. 2002 May 10;296(5570):1087-91. Epub 2002 Apr 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉United States Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA. lsoderblom@usgs.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11934989" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon/analysis ; Cosmic Dust ; Hydrocarbons/analysis ; *Meteoroids ; Spectrum Analysis ; Temperature
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Gravity Waves in Jupiter's Thermosphere (1997)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1997-04-04
    Description: The Atmosphere Structure Instrument on the Galileo probe detected wavelike temperature fluctuations superimposed on a 700-kelvin temperature increase in Jupiter's thermosphere. These fluctuations are consistent with gravity waves that are viscously damped in the thermosphere. Moreover, heating by these waves can explain the temperature increase measured by the probe. This heating mechanism should be applicable to the thermospheres of the other giant planets and may help solve the long-standing question of the source of their high thermospheric temperatures.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Young -- Yelle -- Seiff -- Kirk -- New York, N.Y. -- Science. 1997 Apr 4;276(5309):108-11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉L. A. Young and R. V. Yelle, Center for Space Physics, Boston University, Boston, MA 02215, USA. R. Young, Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA. A. Seiff, Department of Meteorology, San Jose State University Foundation, CA 95192, USA. D. B. Kirk, University of Oregon, Eugene, OR 97403, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9082979" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    The Effect of Surface Roughness on Triton's Volatile Distribution (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-03-20
    Description: Calculations of radiative equilibrium temperatures on Triton's rough surface suggest that significant condensation of N(2) may be occurring in the northern equatorial regions, despite their relatively dark appearance. The bright frost is not apparent in the Voyager images because it tends to be concentrated in relatively unilluminated facets of the surface. This patchwork of bright frost-covered regions and darker bare ground may be distributed on scales smaller than that of the Voyager resolution; as a result the northern equatorial regions may appear relatively dark. This hypothesis also accounts for the observed wind direction in the southern hemisphere because it implies that the equatorial regions are warmer than the south polar regions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Yelle, R V -- New York, N.Y. -- Science. 1992 Mar 20;255(5051):1553-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17820167" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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