Scientists
have found signs that water may once have gurgled up through the Martian soil
in hydrothermal vents similar to those in Yellowstone National Park.
The site of
these proposed vents could possibly contain preserved traces of ancient Martian
life, scientists say. That assumes, of course, that life might once have
existed on Mars. No firm evidence for that idea has ever been found, however.
The vents
evidence comes from NASA's Mars Exploration
Rover Spirit. The robotic explorer found deposits of pure silica, a form of
the element silicon that occurs when hot water reacts with rocks (quartz is a
pure silica), in Mars' Gusev Crater in 2007. The discovery was announced
briefly at the time, but scientists have now had time to fully analyze the
deposits. The results are detailed in the May 23 issue of the journal Science.
Silica
surprise
The silica
was found when Spirit was exploring the Columbia Hills, which rise 300 feet
(100 meters) from the middle of the flat lava plain that fills Gusev Crater.
Scientists were uncertain about just what had formed these hills.
While
Spirit was parked near an area known as the Tyrone site, mission scientists
used the rover's Miniature Thermal Emission Spectrometer (Mini-TES) to look at
some nearby "knobby outcrops," said study team member Steven Ruff of Arizona State University.
"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," Ruff said.
Surveys of
other crops showed the same hints
of silica, but were likewise contaminated. That's when the rover's jammed
right front wheel came to the rescue. As the rover was driving in reverse, its
crippled wheel dug a trench behind it.
"We
aimed the Mini-TES at the trench and it showed a clear silica spectrum,"
Ruff said. They also analyzed the trench's white soil with the rover's Alpha
Particle X-Ray Spectrometer which showed that the soil was more than 90 percent
silica. "That a record high for silica on Mars," Ruff said.
Hot
habitat for life?
Making such
pure silica requires a lot of hot water, Ruff said. "On Earth, the only
way to have this kind of silica enrichment is by hot water reacting with rocks,"
he said, making the connection to hydrothermal vents.
This
relationship also links the silica to Home Plate, a football field-sized
volcanic feature in the Columbia Hills. "Home Plate came from an explosive
volcanic event with water or ice being involved," Ruff explained.
The team
eventually found silica deposits in many other places nearby. Because
hydrothermal vents on Earth harbor life, scientists suspect that they may once
have done so on Mars. And the trace could be
left in the silica deposits.
"On
Earth, hydrothermal deposits teem with life and the associated silica deposits
typically contain fossil remains of microbes," said study team member Jack
Farmer, also of ASU.
"But
we don't know if that's the case here," he added, "because the rovers
don't carry instruments that can detect microscopic life."
The site
stands in contrast to the one that NASA hopes will be explored by its Phoenix
Mars Lander starting next week, because while Phoenix will be looking at
the potential habitability of Mars' north polar region today and in the more
recent geologic past, the silica deposits in Gusev Crater represent a
"possible habitable environment of Mars' ancient past," Ruff told SPACE.com.
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