Scientists are busy revising their assumptions about the red planet as a result of information gleaned from Europe's Mars Express orbiter.

"Our perception of Mars is changing rapidly," notes Gerhard Neukum, principal investigator for the high-resolution stereo camera on Mars Express. But the inflow of data from the spacecraft's various sensors also is triggering calls for further flights to resolve ambiguities raised by current missions. Mars Express, which carried the Beagle 2 lander, was launched in June 2003 and reached Martian orbit six months later.

Many questions were posed, but not necessarily answered, last month at the first gathering here of scientists to review Mars Express findings. Foremost among the queries was whether the potential existence of bacterial life on the planet could be validated. An informal poll among the attendees indicated that 75% believed such life existed on Mars; a further 25% said it could exist today, noted Everett K. Gibson, a senior scientist at Johnson Space Center in Houston. However, he added, to fully resolve the "life" question would require another trip to the planet's surface, or even a sample-return mission.

The genesis of the "life" debate stems from data collected by the Planetary Fourier Spectrometer (PFS). Principal investigator Vittorio Formisano cites the finding of methane and formaldehyde. Methane is a "biomarker," he notes. And the formaldehyde is likely oxidized methane, which experiments in Germany appear to be validating, he argues. There is a correlation between high water-vapor concentrations and those of methane, he says, which suggests a link. However, he concedes that "much more work" needs to be done to draw a final conclusion. But, "for the moment, it seems life is probably the only source that can point to so much methane."

Other explanations for the methane presence include geological processes, such as volcanic or hydrothermal activities, or other outside influences. "We'd like to be able to be there, and drill and find out if there's methane beneath the surface [and if there] are organisms in that water/ice mass," Gibson says. However, he noted that a hydrothermal source would suggest "hot spots" of methane, which so far haven't been observed. He also pointed out that comet or meteorite activity could generate methane, but not at the levels detected.

Scientists are correlating data from the PFS with other Mars Express sensors to try to extract additional information, although that process is largely just beginning.

Further complicating the debate over the methane's origin is that Mars Express may have observed current volcanic activity. Neukum cites findings from the High-Resolution Stereo Camera that reveal not just frozen seas measuring 800 X 900 km. (AW&ST Feb. 28, p. 18) but that also spotlight volcanic cones several kilometers wide. In fact, Neukum says some images show "emerging cones," leading him to argue that there may be "ongoing volcanic activity."

Mars Express also detected solar wind blowing away planetary ions and materials at a rate of about 100 tons per day. The observation that planetary wind is leading to the escape of oxygen and carbon dioxide raises the question of whether water escaped that way as well, says Stas Barabash, principal investigator for the Aspera Energetic Neutral Atoms Analyzer. This area will be the focus of research during the next year, he indicated.

The Mars Radio Science Experiment team reports that, prior to sunrise, the planet's ionosphere is replenished by electrons and other charged particles through solar radiation. Moreover, principal investigator Martin Paetzold says carbon dioxide snowfall is observed at the high-latitude southern winter atmosphere.

In the case of the Spicam Ultraviolet and Infrared Atmospheric Spectrometer team, principal investigator Jean-Loup Bertaux notes that Mars appears to have little ozone and a lot of solar ultraviolet rays at ground level. Moreover, nitric oxide forms on the planet's night side. In part, the atmospheric characterization is intended to help in the design of future aerobraking and landing systems for follow-on missions.

Mars was also found to have sulfate-rich areas, leading scientists to speculate that prior to entering its dry and cold period three billion years ago, Mars may have had warm and wet periods. The sulfate finding is the result of observations by the Omega Visible and Infrared Mineralogical Mapping Spectrometer.