[meteorite-list] Mars Rover Investigates Signs of Steamy Martian Past

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 10 Dec 2007 18:20:05 -0800 (PST)
Message-ID: <200712110220.SAA01262_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2007-144

Mars Rover Investigates Signs of Steamy Martian Past
December 10, 2007

SAN FRANCISCO - Researchers using NASA's twin Mars rovers are sorting
out two possible origins for one of Spirit's most important discoveries,
while also getting Spirit to a favorable spot for surviving the next
Martian winter.

The puzzle is what produced a patch of nearly pure silica -- the main
ingredient of window glass -- that Spirit found last May. It could have
come from either a hot-spring environment or an environment called a
fumarole, in which acidic steam rises through cracks. On Earth, both of
these types of settings teem with microbial life.

"Whichever of those conditions produced it, this concentration of silica
is probably the most significant discovery by Spirit for revealing a
habitable niche that existed on Mars in the past," said Steve Squyres of
Cornell University, Ithaca, N.Y., principal investigator for the rovers'
science payload. "The evidence is pointing most strongly toward
fumarolic conditions, like you might see in Hawaii and in Iceland.
Compared with deposits formed at hot springs, we know less about how
well fumarolic deposits can preserve microbial fossils. That's something
needing more study here on Earth."

Halfway around Mars from Spirit, Opportunity continues adding
information about types of wet environments on ancient Mars other than
hot springs or fumaroles. It is examining layers exposed inside a
crater, but still near the top of a stack of sulfate-rich layers
hundreds of meters (yards) thick. Scientists read a history of
conditions that evolved from wetter to drier, based on findings by
Opportunity and observations of the region by Mars orbiters.

The solar-powered rovers have been active on Mars since January 2004,
more than 15 times longer than originally planned. Their third Martian
winter will not reach minimum sunshine until June, but Spirit already
needs two days of power output to drive for an hour.

"Spirit is going into the winter with much more dust on its solar panels
than in previous years," said John Callas of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., project manager for the rovers. "The last
Martian winter, we didn't move Spirit for about seven months. This time,
the rover is likely to be stationary longer and with significantly lower
available energy each Martian day."

Dust storms that darkened Martian skies this past June dropped dust onto
both rovers. However, gusts cleaned Opportunity's panels, and
Opportunity is closer to the equator than Spirit is, so concerns for
winter survival focus on Spirit. The team has selected a sun-facing
slope of about 25 degrees on the northern edge of a low plateau, "Home
Plate," as a safe winter haven for Spirit.

Both rovers resumed productive field work after the June dust storms.
Spirit explored the top of Home Plate, in the vicinity of silica-rich
soil it discovered before the dust storms hit.

"This stuff is more than 90 percent silica," Squyres said. "There aren't
many ways to explain a concentration so high." One way is to selectively
remove silica from the native volcanic rocks and concentrate it in the
deposits Spirit found. Hot springs can do that, dissolving silica at
high heat and then dropping it out of solution as the water cools.
Another way is to selectively remove almost everything else and leave
the silica behind. Acidic steam at fumaroles can do that. Scientists are
still assessing both possible origins. One reason Squyres favors the
fumarole story is that the silica-rich soil on Mars has an enhanced
level of titanium. On Earth, titanium levels are relatively high in some
fumarolic deposits.

Mineral mapping and high-resolution imagery from Mars orbiters are
helping scientists put the findings of Spirit and Opportunity into
broader geological context. Opportunity's exploration of the Meridiani
region has taken advantage of the natural excavations at impact craters
to inspect layers extending several meters below the surface of the
regional plain. These sulfate-rich layers bear extensive evidence for a
wet, acidic past environment. They are a small upper fraction of the
sulfate-rich layering exposed elsewhere in Meridiani and examined from
orbit.

"We see evidence from orbit for clay minerals under the layered sulfate
materials," said Ray Arvidson of Washington University in St. Louis,
deputy principal investigator for the rovers' science payload. "They
indicate less acidic conditions. The big picture appears to be a change
from a more open hydrological system, with rainfall, to more arid
conditions with groundwater rising to the surface and evaporating,
leaving sulfate salts behind."

JPL, a division of California Institute of Technology, Pasadena, manages
the rovers for NASA's Science Mission Directorate.

For images and information about the rovers, visit: www.nasa.gov/rovers
and http://marsrovers.jpl.nasa.gov .

------------------------------------------------------------------------

Media Contact: Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

2007-144
Received on Mon 10 Dec 2007 09:20:05 PM PST