By Marc Kaufman
Washington Post Staff Writer
Monday, April 28, 2008
SANTA CLARA, Calif. -- The long and frustrating search for signs of past or present life on Mars took a hopeful turn this month when scientists said they had spotted what they believe are remains of two hot springs -- the kind of warm, protected environments where many scientists think primitive life can thrive.
The researchers said water is not flowing now at the sites, but photographs suggest that it may well have bubbled out of the ground in the relatively recent past -- in planetary terms -- meaning tens of millions, rather than billions, of years ago.
"This is the first time that features that are so close in all of their shapes and details to springs on Earth have been reported and identified on Mars," said Carlton Allen of NASA's Johnson Space Center, who is studying the planet to find interesting landing places for future missions. "This puts the story of water on the Martian surface in a totally different context."
The NASA approach to finding life beyond Earth has been "follow the water," on the assumption that any life form is likely to need water, especially warm, liquid water. Not all scientists agree with that notion, saying that life could develop in other mediums, such as liquid methane or ethane. But any discovery that points to the presence of liquid water elsewhere in the universe is big news.
The new images of what Allen and NASA colleague Dorothy Oehler call "mounds" were taken by the Mars Reconnaissance Orbiter, a NASA spacecraft that has taken photos of unprecedented detail and clarity since it began orbiting the planet in 2006. Allen said that similar formations may be common on Mars -- as they are on Earth, which has about 50,000 flowing hot springs -- and that researchers will now look for them elsewhere with the vastly improved imaging.
Allen and Oehler said the mounds have distinctive curved boundaries, a sagging bowl at the top, narrow curving channels that snake around the terrain below and the terraced appearance found at some hot springs in Yellowstone National Park. The elliptical mounds are located in the Vernal crater, which is 2 billion to 4 billion years old and is located near the Martian equator; Oehler said they are believed to be as large as 80 feet high, 650 feet wide and two to three times that in length.
"The whole thing just shouted water and a hot spring," said Allen, who has spent time at Yellowstone studying the hot springs there. "It's so close to what we see on Earth."
Oehler, who used to work as a geologist for an oil company, first identified the mounds and presented the observations this month at a NASA-sponsored conference on astrobiology, the study of life beyond Earth.
She compared images of the Martian mounds taken by the High Resolution Imaging Science Experiment (HiRISE) camera aboard the spacecraft with satellite photos of dry hot springs in central Australia, which looked remarkably similar.
"We're able to report this because we now have the right eyes to see it," Allen said later.
While the researchers think they likely found a former Martian hot spring, they know they lack important confirmatory evidence. The orbiter used a sophisticated spectrometer to analyze the mineral contents of the area around the mounds, which would be expected to include silicate and carbonate if hot springs once flowed there. The instrument failed to detect those minerals.
Oehler and Allen said the dusty Martian surface might have affected those results, but until such minerals are found the mounds cannot be firmly identified as former hot springs.
Michael Meyer, NASA's chief scientist for Mars, said the findings are intriguing but remain preliminary.
"The discovery of a hot springs would be a very significant one, but making that determination is very difficult based only on data from orbit," he said. "It's very interesting to the Mars community, but it will be open to interpretation."
In late 2006, for instance, a comparison of photographs taken several years apart by another spacecraft, NASA's Mars Global Surveyor, showed that two gullies had appeared on the slope of a crater, suggesting that water might have flowed there in the interval. The report caused great excitement, but scientists have since moved toward the view that the gullies were formed by a slide of loose, dry material, not by flowing water.
Meyer said that the findings of that report were clearly "not a slam-dunk" but that the likelihood remains that there is some liquid water beneath the planet's surface.
Such water would be substantially cooler than in Earth's hot springs, since Mars is colder, and its thinner atmosphere allows water to boil at about 50 degrees Fahrenheit, as opposed to 212 degrees on Earth. That means Martian water would not get any hotter than roughly room temperature, which certainly could support life.
NASA is planning to send a manned mission to Mars sometime after 2030, but in the interim the agency plans to study the planet further with increasingly sophisticated cameras, rovers and a mission to gather Martian samples and bring them back to Earth.
Next month, the Phoenix Mars Lander, a robotic laboratory, is scheduled to land on the largest concentration of Martian ice outside of the polar regions. It is designed to dig into the ice and sample it for microbial life as well as for signs of climate changes. And NASA's two earlier rovers, Spirit and Opportunity, continue to explore the planet almost 4 1/2 years after they landed.
Working with European partners, NASA is planning a mission within a decade to collect rock and dirt samples and return them to Earth. The project has run into budget problems, however, as well as concerns over the risks of bringing back Martian rocks that could contain organisms.
Oehler and Allen said they hope future missions will consider exploring the suspected hot springs -- which are ideal not only for encouraging life but also for fossilizing remains.
"We know from Earth that life might have started in hydrothermal environments like hot springs, and has lasted and been preserved in them," Oehler said. "It could also be true on Mars."