Rosetta-Alice observations of exospheric hydrogen and oxygen on Mars

• Published in: Icarus (New York, N.Y. 1962) Vol. 214; no. 2; pp. 394 - 399
• Main Authors: Feldman, Paul D., Steffl, Andrew J., Parker, Joel Wm, A’Hearn, Michael F., Bertaux, Jean-Loup, Alan Stern, S., Weaver, Harold A., Slater, David C., Versteeg, Maarten, Throop, Henry B., Cunningham, Nathaniel J., Feaga, Lori M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-08-2011; Elsevier
• Subjects: Astronomy; Astrophysics; Atmospheres, Evolution; Earth and Planetary Astrophysics; Earth, ocean, space; Exact sciences and technology; Mars; Mars, Atmosphere; Physics; Sciences of the Universe; Solar system; Mars; Atmospheres, Evolution; Mars, Atmosphere; Comets; Spectroscopy; Ultraviolet imaging; Atmospheres; Rosetta space probe; Dissociative recombination; Planets; Atmosphere; Evolution; Models; Upper atmosphere; Solar system; Gravity
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2011.06.013

►
Rosetta fly-by of Mars in 2007 provides new UV data on H and O in Mars’ exosphere. ► H observed out to 30,000
km planetocentric distance. ► H spatial distribution fit with single temperature Chamberlain model. ► O spatial distribution fit with a two-temperature component model.
The European Space Agency’s
Rosetta spacecraft, en route to a 2014 encounter with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on 25 February 2007, closest approach being at 01:54
UT. The Alice instrument on board
Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for
in situ cometary spectroscopy in the 750–2000
Å spectral band, was used to study the daytime Mars upper atmosphere including emissions from exospheric hydrogen and oxygen. Offset pointing, obtained five hours before closest approach, enabled us to detect and map the H
i
Lyman-α and Lyman-β emissions from exospheric hydrogen out beyond 30,000
km from the planet’s center. These data are fit with a Chamberlain exospheric model from which we derive the hydrogen density at the 200
km exobase and the H escape flux. The results are comparable to those found from the Ultraviolet Spectrometer experiment on the
Mariner 6 and
7 fly-bys of Mars in 1969. Atomic oxygen emission at 1304
Å is detected at altitudes of 400–1000
km above the limb during limb scans shortly after closest approach. However, the derived oxygen scale height is not consistent with recent models of oxygen escape based on the production of suprathermal oxygen atoms by the dissociative recombination of
O
2
+
.