[meteorite-list] Mars Rover Finds Yellowstone-like Hot Spring Deposits

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 23 May 2008 13:49:43 -0700 (PDT)
Message-ID: <200805232049.NAA10165_at_zagami.jpl.nasa.gov>

Arizona State University
Tempe, Arizona

Contact:
Robert Burnham, 480-458-8207

May 22, 2008

Mars rover finds Yellowstone-like hot spring deposits

Deposits of nearly pure silica discovered by the Mars Exploration Rover
Spirit in Gusev Crater formed when volcanic steam or hot water (or maybe
both) percolated through the ground. Such deposits are found around
hydrothermal vents like those in Yellowstone National Park. That's the
conclusion of planetary scientists working with data collected by the
rover's mineral-scouting instrument, which was developed at Arizona State
University.

The silica discovery, announced briefly by NASA in 2007, is fully described
in a multi-author paper that appears in the May 23, 2008 issue of the
scientific journal Science. The lead author is Steven Squyres of Cornell
University, principal investigator for the rover science payload.

The silica finding turns a spotlight on an important site that may contain
preserved traces of ancient Martian life.

"On Earth, hydrothermal deposits teem with life and the associated silica
deposits typically contain fossil remains of microbes," says Jack Farmer,
professor of astrobiology in ASU's School of Earth and Space Exploration,
part of the College of Liberal Arts and Sciences. Farmer is one of the
paper's co-authors.

"But we don't know if that's the case here," Farmer notes, "because the
rovers don't carry instruments that can detect microscopic life." He adds,
"What we can say is that this was once a habitable environment where liquid
water and the energy needed for life were present."

NASA landed the two Mars rovers, Spirit and Opportunity, on opposite sides
of the planet in January 2004 to look for rocks showing the presence of
water. As of now, the rovers are more than four Earth years into a mission
designed to last just three months. Despite dust collecting on their solar
panels and mechanical wear-and-tear, both are continuing to explore.

Dawning realization

The silica discovery unfolded in slow motion as Spirit emerged from
hibernation after its second Martian winter. The rover spent those months on
the edge of a football-field-size feature dubbed Home Plate.

Home Plate lies in the Columbia Hills, a range of low hills in the middle of
Gusev Crater, which spans 100 miles (170 kilometers) wide. The Hills rise
about 300 feet (100 meters) above the flat lava plain that fills Gusev, but
their structure and origin remain unclear to scientists.

"We were going back to an area of exposed soil called the Tyrone site, which
we didn't have time to investigate before winter began," notes Steven Ruff,
a faculty research associate at ASU's Mars Space Flight Facility. Ruff is
another of the paper's co-authors.

The Tyrone soil proved rich in sulfate minerals, a phenomenon seen by Spirit
at other locations in the Columbia Hills, where Spirit has been exploring
since late 2004. While sulfates can form in several ways, water is involved
in most.

"While parked next to Tyrone, we used the Mini-TES to look at some nearby
light-toned and knobby outcrops," says Ruff.

Mini-TES is short for the Miniature Thermal Emission Spectrometer, an
instrument placed on each rover to identify minerals by their infrared
spectrum. Ruff is the scientist in charge of day-to-day operations for
Mini-TES, which was designed by ASU's Philip Christensen, a Regents'
Professor of Geological Sciences and director of the Mars Space Flight
Facility.

Silica surprise

Ruff continues, "It wasn't clear what we were seeing in the knobby outcrops
because they were contaminated with dust and wind-blown soil. But I thought
they might be silica-rich." Additional surveys with Mini-TES identified
other outcrops, similarly contaminated but likewise hinting at silica.

As it happened, the rover's jammed right front wheel inadvertently produced
the "Aha!" moment. Ruff and others on the science team noticed that the
stuck wheel had gouged a trench a few inches deep through the soil as the
rover drove ahead in reverse, dragging the crippled wheel behind.

"The trench looked bright white," Ruff recalls, "but we thought initially it
was just more sulfate minerals."

Over the winter, however, Ruff got curious. "We aimed Mini-TES at the trench
and it showed a clear silica spectrum. This prompted us to drive back to it,
where the rover's Alpha Particle X-Ray Spectrometer told us the white soil
was more than 90 percent silica. That's a record high for silica on Mars."

Fumaroles and hot springs

Making such pure silica requires a lot of water, says Ruff. "On Earth, the
only way to have this kind of silica enrichment is by hot water reacting
with rocks."

This, Ruff says, links the silica with Home Plate, which the rover team
already knew was a volcanic feature. "Home Plate came from an explosive
volcanic event with water or ice being involved," he explains. "We saw where
rocks were thrown into the air and landed to make small indentations in the
soft, wet ash sediment around the vent."

Once alerted what to look for, the scientists found more silica in many
places nearby.

As Ruff explains, "It's not just the soil in a trench in one place. It's a
broader story of outcrops that extend 50 meters [about 150 feet] away from
Home Plate. It's not a small scale, modest phenomenon."

The combination of geothermal heat and water produces a hydrothermal system
like that which powers the hot springs, geysers, mudpots, and fumaroles
(steam vents) of Yellowstone National Park.

Capturing evidence

Astrobiologist Farmer helped with the mineral identification by supplying a
variety of high silica rock samples from his laboratory collection. They
included rocks from hot spring and fumarole deposits in Yellowstone and New
Zealand. These rocks provided reference spectra for Mini-TES. "The best fit
we got was with siliceous sinter," he says, referring to deposits of "opal,"
a type of amorphous silica laid down by hot springs.

Farmer explains that hydrothermal systems generally precipitate silica and
other minerals as heated groundwater rises, cools, and gives off dissolved
gases. "If there were organisms living there," he says, "our terrestrial
experience shows that microbes can easily be entrapped and preserved in the
deposits." Silica, he notes, is an excellent medium for capturing and
preserving traces of microbial life.

Whether Mars ever had life is unknown. But if there was once a Martian
biosphere, both Ruff and Farmer say the deposits around fumaroles and hot
springs are ideal places to start hunting for it.

Although the microscopic imagers on the current rovers cannot resolve the
microbial remains seen in terrestrial hot spring deposits, Farmer notes that
the new microscopic imagers now in development for future rovers should let
scientists detect such features in situ.

Says Farmer, "We just need to deliver such instruments to the right place.
The discoveries at Home Plate have helped us know where to go next."

Ruff adds, "This discovery has us really excited. This site is clearly the
best example of a habitable environment that we've found in Gusev."

IMAGE CAPTION:
[http://asunews.asu.edu/files/images/4_filaments.jpg (413KB)]
Silica layers coat bacterial filaments in a sample from Excelsior Geyser
Crater, Grand Prismatic Spring, Yellowstone National Park. The silica
coating preserves microbial structures. Scientists hunting for a Martian
biology might start by searching for similar structures in Martian hot
spring deposits. Photo credit: Arizona State University/Jack Farmer
Received on Fri 23 May 2008 04:49:43 PM PDT


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