• Determine the interaction of the solar wind with Mars;

  • Determine diurnal and seasonal variations of Mars’s upper atmosphere and ionosphere;

  • Determine the influence of the crustal magnetic field on ionospheric processes;

  • Measure thermal and nonthermal escape rates of atmospheric constituents and estimate the evolution of the martian atmosphere;

  • Measure composition and winds in the middle atmosphere; and

  • Address in detail the issue of methane and other trace gases in the bulk atmosphere.

The selection in early 2007 of two Scout concept missions, both addressing the structure and dynamics of Mars’s upper atmosphere, as candidates for the 2011 launch opportunity has cast some uncertainty as to the scientific scope of the mission to be flown in 2013. Since MAVEN and The Great Escape both address some of the goals listed above, the exact scientific scope of the 2013 orbiter is currently being reevaluated. Whatever the outcome of the current rescoping, this spacecraft will likely have a secondary role as a telecommunications relay to enhance the data return from surface missions such as MSL (if it is still operating) and subsequent landed missions. The dual science and mission-support role of MSTO presents issues concerning the selection of appropriate orbits. The different science goals would likely benefit from different orbits, and the telecommunications goal would require yet another orbit. Approaches could involve either compromises on the orbit or changing orbits midway through the mission.

ExoMars

ExoMars is the first flagship mission in the ESA’s Aurora program of robotic and human exploration of the planets. It is a highly ambitious project involving a rover, an instrumented lander, and, possibly, an orbiting communications relay.8 The rover was conceived as being of roughly the same size as a Mars Exploration Rover, but having the ability to carry an MSL-class payload. The science goals of ExoMars are the following:

  • Search for signs of past and present life on Mars;

  • Characterize the geochemistry of and distribution of water in the near-surface regolith;

  • Measure the geophysical characteristics of the martian environment; and

  • Identify possible surface hazards to future human missions.

These goals will be addressed by Pasteur, a comprehensive set of scientific instruments mounted on the rover, and by a separate geophysics/environmental package on the landing platform. ExoMars is currently scheduled for launch in 2013. The ambitious Pasteur package consists of remote-sensing, contact, and analytic instruments supported by a complex sample-handling system and a drill capable of extracting samples from depths of 1 to 2 meters. The latter may be particularly important if putative organic compounds, preserved in the subsurface regolith from the harsh oxidizing surface conditions, are to be studied. Instruments of particular relevance to astrobiology include a Raman/laser-induced-breakdown spectroscope, an organics and oxidants detector, a gas chromatograph-mass spectrometer, and gas and antibody-based microarray organics detectors. The results, positive or negative, from the Pasteur instruments capable of detecting organic molecules at very high sensitivity (parts per billion and better) may be key to future astrobiological studies of Mars. Overall, ExoMars has great scientific potential, and its timing relative to the Mars Science Laboratory and the Astrobiology Field Laboratory may prove particularly fortuitous.

Astrobiology Field Laboratory

The Astrobiology Field Laboratory (AFL) mission is conceived as being a highly capable rover derived from the Mars Science Laboratory. Its principal goals would be to assess the biological potential of sites, interpret the paleo-climate record, and search for biosignatures of ancient and modern life. This mission concept postdates the publication of the SSE decadal survey, and it is important to note that its origins are more programmatic than



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