ITHACA, N.Y. — Scientists have long been tantalized by the question of
whether life once existed on Mars. Although present conditions on the
planet would seem to be inhospitable to life, the data sent back over the
past 10 months by NASA’s two exploration rovers, Spirit and Opportunity,
showed a world that might once have been warmer and wetter — perhaps
friendly enough to support microbial organisms.

Now a Cornell University-led Mars rover science team reports on the
historic journey by the rover Opportunity, which is exploring a vast
plain, Meridiani Planum, and concludes with this observation: “Liquid
water was once present intermittently at the martian surface at Meridiani,
and at times it saturated the subsurface. Because liquid water is a key
prerequisite for life, we infer that conditions at Meridiani may have
been habitable for some period of time in martian history.”

The article is one of 11 published this week (Dec. 3, 2004) in a special
issue of the journal Science, authored by scientists connected with the
Mars rover mission, several from Cornell and from the Jet Propulsion
Laboratory in Pasadena, Calif., the mission’s manager. The issue covers
Opportunity through its first 90 days of exploring its landing site of
Eagle crater in Meridiani Planum. This was before the rover drove to and
entered the large crater dubbed Endurance, from which it is now about to

Steve Squyres, Cornell professor of astronomy and leader of th rovers’
Athena science team, is the lead author of the main paper, “The
Opportunity Rover’s Athena Science Investigation at Meridiani Planum,
Mars.” In another paper, on which he is also the lead author, Squyres
again refers to the geological record at Meridiani Planum as suggesting
that conditions were suitable for “biological activity” for a period of
time in the history of Mars. In the article, “In Situ Evidence for an
Ancient Aqueous Environment at Meridiani Planum, Mars,” he writes: “We
cannot determine whether life was present or even possible in the waters
at Meridiani, but it is clear that by the time the sedimentary rocks in
Eagle crater were deposited, Mars and Earth had already gone down
different environmental paths. Sample return of Meridiani rocks might well
provide more certainty regarding whether life developed on Mars.”

The Mars rover mission is not designed to look for microbial life but to
look for evidence of whether conditions were once right for life. As
Squyres recently stated, “What we were seeking was rocks that were
actually formed in liquid water so that we could read the record in those
rocks, not just to say liquid water was on Mars but to learn something
about what the environmental conditions were like, would they have been
suitable for life and, importantly, do the minerals that were formed have
the capability to preserve for long periods of time evidence of former
life? That’s probably the single most important thing we have found:
evidence for minerals at Meridiani that are the kinds of things that are
very good at preserving evidence of ancient life for very long periods of

Opportunity bounced down on Jan. 25, 22 days after its twin, the rover
Spirit, landed on the opposite side of Mars in Gusev crater. Last August
Science published a special issue on Spirit.

“This is the first peer-reviewed presentation of the data from
Oportunity,” notes Jim Bell, Cornell associate professor of astronomy and
the lead scientist for the rovers’ Pancam color imaging system.

Bell also is prominent in the special issue of Science, including his lead
authorship of a paper, “Pancam Multispectral Imaging Results from the
Opportunity Rover at Meridiani Planum.”

When Opportunity landed on the red planet last January, the robot
geologist sent back images of its landing site that were unlike any of the
other places where earlier lander probes and rovers had gone. Instead of
rusty deserts of dusty soil and boulders strewn to the horizon,
Opportunity had landed in a relatively small crater in a vast sea of sand
nearly devoid of rocks. Fortunately, an intriguing outcrop of bedrock
presented itself nearby, which scientists hoped would be a sample of the
original crust underneath the layers of dust.

The scientists were not disappointed. Scattered among the outcrop rocks
were large numbers of small, round mineral deposits that the Athena
science team named “blueberries.” On Earth, such formations appear when
large amounts of water course through rock layers, leaching out the
iron–bearing minerals into small spherical rocks and granules. The rovers
detected large amounts of sulfate salt deposits. Enough evidence was
collected by Opportunity in the two months it spent examining Eagle crater
that the science team felt confident enough to announce in early March
that liquid water had flowed over the crater’s rocks long ago, possibly
for a long time. Following on this, the latest Science articles largely
focus on Opportunity’s most important scientific and geological
accomplishment: the discovery of evidence that liquid water once flowed
through the region.

Like the coverage given to Spirit in the August issue of Science, the
latest edition contains several foldouts with big color panoramas and
images from Opportunity’s region of exploration.

Freelance writer Larry Klaes contributed to this report.