Sushil Atreya's Research

RESEARCH
Sushil Atreya's research focuses on crosscutting themes of the origin and evolution of the solar system and the exoplanet atmospheres, planetary habitability, and the climate evolution. His principal areas of expertise include coupled chemistry-clouds-composition processes, interior-surface-atmosphere interactions, and the comparative structure and composition of planetary atmospheres. For nearly four decades, Sushil Atreya has also been actively engaged in the development of future planetary exploration mission concepts, including in situ exploration with entry probes to the gas and icy giant planets and Venus and landed missions at Mars. Specifics are listed under Research Highlights, Major Professional Activities, and Publications.

RESEARCH HIGHLIGHTS
A sampling of Sushil Atreya's significant research contributions:

First high precision measurement of primordial argon isotope ratio on Mars, which shows that Mars has lost much of its original atmosphere in the past four billion years, and the ratio also provides conclusive evidence that the so called martian meteorites are indeed rocks from Mars.
Significant contributions to and interpretation of the determination of the abundance of water and ammonia in the deep atmosphere of Jupiter, using Juno’s microwave radiometer.
Key role in the first direct, in situ detection of methane and its unexpected seasonal variability on Mars by the Curiosity Rover, which has brought us ever closer to unraveling the mystery of past or present microbial life on Mars.
Comprehensive models and scenarios of the sources and sinks of methane on Mars that are key to understanding the biological potential of Mars and the planet's present and past habitability.
Key role in the first observations of seasonal variation of oxygen on Mars, which shows unexpected rise in oxygen beginning in the spring and continuing through summer, indicating a surface flux of oxygen, possibly related to surface oxidants.
Detection of organics in the fines of ancient mudstones on the surface of Mars by Curiosity Rover using the Sample Analysis suite of instruments.
Methane cycle on Titan, based on the data collected by the Cassini-Huygens mission. The cycle reveals plausible scenarios for the origin, loss, surface evaporation, and rain/snow-out of methane on Titan, and that Titan's global cycle of methane is similar to the hydrological cycle on Earth. Methane is also critical to the maintenance of a stable atmosphere of nitrogen on Titan.
Origin of Titan's atmosphere. Developed photochemical models of the formation of nitrogen on Titan, before the gas was detected on Titan. The models showed that a massive atmosphere of nitrogen would result from the photolysis of a nitrogen-bearing molecule, most likely ammonia. Nitrogen was later inferred indirectly in the troposphere of Titan by Voyager in 1980 and measured directly by the Huygens entry probe in situ in 2005.
Discovery of heavy element enrichment in Jupiter relative to solar with the Galileo entry probe team, which led to the icy planetesimal model of Jupiter's formation.
Composition and structure of the atmospheres of all giant planets, including many first determinations of vertical mixing, trace constituents, chemical and cloud processes.
Composition and structure of the giant planet ionospheres, including prediction of metallic ion layers, before the Pioneer spacecraft at Jupiter made first measurements in 1974.
First model of the triboelectric field induced electrochemistry in the Martian dust devils and storms, with possible implications for destruction of surface organics.
Photochemical stability of the Martian atmosphere, including the role of catalytic heterogeneous processes.
First ever determination of the molecular hydrogen density height profile in the earth's upper atmosphere, which has important implications for the evolution of planetary atmospheres.
Prediction of H₂CN⁺ as the major ion of the ionosphere of Titan, before an ionosphere was even measured (by Voyager in 1980). In 2005, Cassini orbiter confirmed H₂CN⁺ as Titan's major ionospheric species.

MAJOR PROFESSIONAL ACTIVITIES

Solar System Exploration Missions Co-Investigator and Science Team Member
Sushil Atreya has played a key role on a number of solar system exploration missions of NASA, ESA, JAXA, and the former Soviet Union, starting with pre-proposal concept development in many instances. A select list of Sushil Atreya's planetary spacecraft mission experience is given below.

DAVINCI (Deep Atmosphere Venus Investigation of Noble gases, Chemistry and Imaging): Atmospheric Origin and Evolution Lead, 2021-Present
JUNO: Jupiter Polar Orbiter, 2004-Present
MSL/CURIOSITY ROVER: Sample Analysis at Mars including gas chromatograph, mass spectrometer and tunable laser spectrometer, 2004-Present
CASSINI-HUYGENS: 1990-2019 (Huygens Gas Chromatograph Mass Spectrometer, and Aerosol Collector Pyrolyzer)
GALILEO: Jupiter Entry Probe Mass Spectrometer, 1977-2003
VOYAGER 1 and 2: Ultraviolet Spectrometer at Jupiter, Saturn, Uranus, Neptune Systems, 1974-1990
EXOMARS (ESA): Mars Organic Molecule Analyzer (MOMA Collaborator on 2022 Rover), 2012-Present
VENUS EXPRESS (ESA): Deputy USA Lead Scientist, and ESA CoI, 2004-2015
MARS EXPRESS (ESA): Planetary Fourier Spectrometer, 1998-Present
PHOBOS 2: Soviet Mars Mission/UV-IR Spectrophotometer "Auguste", 1985-1989
NOZOMI Japanese Mars Mission (JAXA): Neutral Mass Spectrometer, 1995-2004 (failed)
MARS '96: Soviet Mars Mission, U.S. Participating Scientist, 1990-1996 (failed)
CHAMPOLLION/COMET LANDER: Chemical Analysis od Released Gas Experiment, 1995-1999 (canceled)
COMET RENDEZVOUS ASTEROID FLYBY: Neutral Gas and Ion Mass Spectrometer, 1986-1992 (canceled)
Univ. Michigan-NASA Center for Space Terahertz Technology, Executive Committee, 1988-1992
SpaceLab Imaging Spectrometric Observatory, 1977-1984

Guest Observer/Investigator on ISO, HST, Spitzer, IRTF, CFHT, IUE, VLA, and OAO/Copernicus: various years since 1975.

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