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Martian “Yellowstone” might have nourished life

May 22, 2008
Courtesy ASU School of Earth & Space Exploration
and World Science staff

New tests in­di­cate hot wa­ter or steam once soaked Mar­tian soil, in a pos­sibly life-giv­ing pro­cess si­m­i­lar to what goes on at hot springs, sci­en­tists say.

The dis­cov­ery, they add, came thanks to a Mars rov­er’s stuck wheel—which scraped away some top­soil to re­veal plen­ti­ful sil­ica, a min­er­al com­po­nent of both sand and glass. 

As Spir­it drove away from Ty­rone, its jammed right front wheel dug this trench. (Cour­te­sy NA­SA/J­PL/­Cor­nel Uni­ver­si­ty)

Such sil­ica de­posits are found around hot springs, or hy­dro­ther­mal vents, like those in Wyoming’s Yel­low­stone Na­tional Park. 

The Mar­tian sil­ic­a’s pu­r­ity sug­gests it must have formed in si­m­i­lar set­tings, said Ari­zona State Uni­ver­s­ity’s Ste­ven Ruff, one of the sci­en­tists. “On Earth, the only way to have this kind of sil­ica en­rich­ment is by hot wa­ter re­act­ing with rocks.”

That makes the site an ide­al place to look for Mar­tian fos­sils, the re­search­ers added.

Earth’s “hy­dro­ther­mal de­posits” teem with mi­crobes, not­ed Jack Farm­er of the uni­ver­s­ity, an­oth­er of the sci­en­tists in­volved. More­o­ver, he said, sil­ica is ex­cel­lent for pre­serv­ing their fos­sils. Un­for­tu­nately “the rov­ers don’t car­ry in­stru­ments that can de­tect mi­cro­scop­ic life,” he added, but fu­ture mis­sions could in­ves­t­i­gate the ar­ea.

The sil­ica find­ing, an­nounced briefly by NASA last year, is de­scribed in de­tail in a pa­per by Ruff, Farm­er and oth­ers in the May 23 is­sue of the re­search jour­nal Sci­ence. 

The agen­cy sent two rov­ers, Spir­it and Op­por­tun­ity, on op­po­site sides of the red plan­et in 2004. Shortly af­ter emerg­ing from a hi­berna­t­ion in its sec­ond Mar­tian win­ter, Spir­it moved to an ar­ea of ex­posed soil called Ty­rone—in the Co­lum­bia Hill range with­in an ancient-lava-filled crat­er called Gu­sev, sci­en­tists said.

Silica layers coat bacterial fila­ments in a sam­ple from Ex­cel­sior Gey­ser Cra­ter, Grand Pris­ma­tic Spring, Yel­low­stone Na­tion­al Park. The si­li­ca coat­ing pre­serves mi­cro­bi­al struc­tures. (Cour­tesy Ari­zo­na State Uni­ver­s­ity/Jack Far­m­er)

Researchers then used the rov­er to probe some “knobby out­crops,” said Ruff. That’s when a wheel jammed. The ro­bot moved along drag­ging the wheel, carv­ing a gouge that re­vealed a bright white soil. 

Be­fore long, “the rov­er’s Al­pha Par­t­i­cle X-Ray Spec­trom­e­ter told us the white soil was more than 90 per­cent sil­ica,” Ruff said. The de­vice an­a­lyzes min­er­al com­po­si­tion by an­a­lyz­ing X-rays a sam­ple gives off af­ter be­ing pum­meled with radia­t­ion.

The sil­ica is probably as­so­ci­at­ed with a near­by vol­can­ic fea­ture known as Home Plate, Ruff said. “Home Plate came from an ex­plo­sive vol­can­ic event with wa­ter or ice be­ing in­volved,” he ex­plained. “We saw where rocks were thrown in­to the air and land­ed to make small in­denta­t­ions in the soft, wet ash sed­i­ment around the ven­t.”

The sci­en­tists next looked for and found much more sil­ica near­by, Ruff said. “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.”

In­ter­nal planetary heat com­bines with wa­ter to cre­ate a hy­dro­ther­mal sys­tem like that which pow­ers the hot springs, gey­sers, mud­pots, and fu­maroles or steam vents of Yel­low­stone, re­search­ers added. Tests al­so sug­gested the sil­ica mix was of a pre­cise type known as si­li­ceous sin­ter, a va­ri­e­ty of opal laid down by hot springs, said Farm­er: sil­ica and oth­er min­er­als gen­er­ally drop out of wa­ter in hy­dro­ther­mal sys­tems as hot groundwa­ter rises, cools, and gives off dis­solved gas­es.

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New tests indicate hot water or steam once soaked Martian soil, in a possibly life-giving process similar to what goes on at hot springs, scientists say. The discovery, they add, came thanks to a Mars rover’s stuck wheel—which scraped away some topsoil to reveal plentiful silica, a mineral component of both sand and glass. Such silica deposits are found around hot springs, or hydrothermal vents, like those in Wyoming’s Yellowstone National Park.The Martian silica’s purity suggests it must have formed in similar settings, said Arizon State University’s Steven Ruff, one of the scientists. “On Earth, the only way to have this kind of silica enrichment is by hot water reacting with rocks.” That makes the site an ideal place to look for Martian fossils, the researchers added. Earth’s “hydrothermal deposits” teem with microbes, noted Jack Farmer of the university, another of the scientists involved. Moreover, he said, silica is excellent for preserving fossil remains. Unfortunately “the rovers don’t carry instruments that can detect microscopic life,” he added, but future missions could investigate the area. The silica finding, announced briefly by NASA last year, is described in detail in a paper by Ruff, Farmer and others in the May 23 issue of the research journal Science. The agency sent two rovers, Spirit and Opportunity, on opposite sides of the red planet in 2004. Shortly after emerging from a hibernation in its second Martian winter, Spirit moved to an area of exposed soil called the Tyrone site—in the Columbia Hill range within an ancient-lava-filled crater called Gusev, scientists said. Scientists then used the rover to probe some “knobby outcrops,” said Ruff. That’s when a wheel jammed. The robot moved along dragging the wheel, carving a gouge that revealed a bright white soil. Before long, “the rover’s Alpha Particle X-Ray Spectrometer told us the white soil was more than 90 percent silica,” Ruff said. The device analyzes mineral composition by analyzing X-rays a sample gives off after being pummeled with radiation. The silica is probably associated witha nearby volcanic feature known as Home Plate, Ruff said. “Home Plate came from an explosive volcanic event with water or ice being involved,” he explained. “We saw where rocks were thrown into the air and landed to make small indentations in the soft, wet ash sediment around the vent.” The scientists next looked for and found much more silica nearby, Ruff said. “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 planet’s internal heat combines with water to produces a hydrothermal system like that which powers the hot springs, geysers, mudpots, and fumaroles or steam vents of Yellowstone, researchers added. Tests also suggested the silica mix was of a precise type known as siliceous sinter, a variety of opal laid down by hot springs, said Farmer: silica and other minerals generally drop out of water in hydrothermal systems as hot groundwater rises, cools, and gives off dissolved gases.