May 22, 2008
Courtesy ASU School of Earth & Space Exploration
and World Science staff
As Spirit drove away from Tyrone, its jammed right front wheel dug this trench. (Courtesy NASA/JPL/Cornel University)
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.
