Mars orbiter imagery boosts Curiosity rover's life search
BY CRAIG COVAULT
Posted: May 31, 2009
NASA and university scientists reviewing data from the Mars Reconnaissance Orbiter (MRO) say evidence is growing that the planet harbored life in its past or that Martian microbes exist now.
They say their views are based on the growing body of data on the diversity of water related minerals discovered by MRO. It is also supported by findings from other spacecraft such as Europe's Mars Express orbiter and NASA's Phoenix lander and twin Mars rovers.
The MRO data is being used to narrow the best sites to locate life related evidence, while also being safe enough for the Mars Science Laboratory rover "Curiosity" set for launch in 2011.
MRO's high resolution mineralogy data resulted in, for example, the addition of Gale crater to MSL's final landing target list.
The Curiosity rover will carry 10 times the science payload mass of the coffee-table sized Spirit and Opportunity rovers still operating on Mars.
"Every time we go and look at new data from the planet I have gotten more encouraged that the possibility for life at least in Mars' past," says Mike Meyer NASA's lead scientist for Mars exploration.
"There is encouraging new MRO evidence that makes the pursuit of present day life very worthwhile," says Scott Murchie of the Applied Physics Laboratory at Johns Hopkins University, principal investigator of the MRO Compact Reconnaissance Imaging Spectrometer.
"I definitely think there could have been life on Mars," says Richard Zurek, MRO project scientist at JPL.
All three scientists commented on the life issues at a NASA Headquarters briefing on MRO highlights, as the orbiter has just completed its primary science mission and is beginning and extended science mission phase.
"I think there is very encouraging evidence not just to look in the present, but also for what [past life may have come] before during planets evolution," Murchie says. His team's CRISM instrument has returned extensive new evidence on the diversity of water related mineral locations on the planet.
Meyer said the discovery of methane in the current Martian atmosphere as well as evidence of liquid water on the planet today are positive factors toward the potential for current life on Mars.
On Earth methane is a common byproduct of metabolism by life forms. It has been discovered at specific locations in the Martian atmosphere by the European Mars Express Orbiter. In addition Phoenix lander scientists believe their spacecraft splashed up actual liquid water on Mars during its landing on an arctic water ice plane in 2008. Phoenix also detected carbonate related soil chemistry that could support life. MRO is finding similar carbonate chemistry at other locations on Mars.
"I think life could have developed on Mars but whether it is there today I am not so sure," Zurek cautioned however,
Zurek said that MRO and other data has become so compelling on positive factors for at least past Martian life, that an important questions is if no life is found on Mars , why has it not formed, he asked? That would force a major new branch of study on the assessment for diminished chances for life on other bodies besides Earth, in or outside of the solar system he says.
He said that the same ingredients present on Earth when life began to form just a billion years after the planet formed were also present at the same time on Mars, when its climate was warmer and more hospitable to surface life than it is now.
Those include surface and underground water, solar energy and heat and heat from within the planet . All three scientists said underground Mars life may be more likely than surface life just as on Earth where there is more biomass underground than on the surface.
A major emphasis in the new MRO phase will be to search for near real time geologic and aqueous processes that could bear on the current life question, such as detection of real time or recent outbursts of water from the sides of crater walls.
MRO has made some spectacular discoveries that relate to the presence of water or ancient Mars and its abundance at specific locations.
The area, based on CRISM data was initially considered as an MSL landing area but rejected as too hazardous. That does not diminish its significance, however, as an area where life could have formed. Some future rover beyond MSL or even a manned lander may some day visit Nili Fossae based on the MRO imagery.
That MRO imagery shows carbonate minerals (color coded green) indicating that Mars had neutral to alkaline water when the minerals formed at these locations more than 3.6 billion years ago.
Carbonates, which on Earth include limestone and chalk, dissolve quickly in acid. Therefore, their survival until today on Mars challenges suggestions that an exclusively acidic environment later dominated the planet. Instead, it indicates that different types of watery environments existed. The greater the variety of wet environments, the greater the chances one or more of them may have supported life, scientists agree.
"We're excited to have finally found carbonate minerals because they provide more detail about conditions during specific periods of Mars' history," said Murchie.
The best-exposed rocks occur along a Nili Fossae trough system 414 mi. long at the edge of a large basin. The region has rocks rich in olivine, (color coded yellow) a mineral that can react with water to form the carbonate.
"This discovery of carbonates in an intact rock layer, in contact with clays, is an example of how joint observations by CRISM and the telescopic cameras on MRO are revealing details of distinct environments on Mars," said Sue Smrekar, deputy project scientist for the orbiter at JPL. They point to specific locations where future rovers and landers could search for possible evidence of past life, she says.
The image of Gale shown above also shows the candidate MSL landing ellipse within the crater.
CRISM data indicate that water once in the crater left a detailed and layered mineralogical record on the crater walls and around the crater's giant central peak. The peak documents what took place there from the time a giant meteorite initially formed the crater 3 billion years ago, to later periods in Mars history. The oldest exposed rocks are at the top of the central peak. Layering all up and down the peak indicate different water layers in the crater through more recent time since the crater was formed.
If Gale crater is selected, Murchie says MSL rover instruments will look for fossils of past Martian life there as well as less spectacular evidence, like organic bearing rocks that could have been formed with microorganisms present and preserved the chemical signitures of past life.
MRO is also continuing to image three other MSL landing site candidates equally compelling says Zurek. They are:
Marwth Valley: The only MSL candidate landing site in the northern hemisphere is the Marwth Valley area. " It too is important because of the diversity of the mineral signatures that you see," Zurek says. A large channel carved by water cuts across the valley below highlands out of where the water flowed. The highlands also show the effects of water, Zurek says. "There we see different mineral signatures in different layers indicating the episodic activity of water or the mixing of soils by impacts in the early history of Mars," he says.
Holden Crater: In the southern hemisphere of Mars the 60 mi. dia. Holden crater area is also a landing site finalist because of a channel that goes into that crater. MRO data indicate water once flowed into that crater, then formed a lake before it breached the far wall and ran out, leaving layers. "In those layers we would expect to find evidence of the past chemistry, the action of water, and how long it was there," says Zurek. "They may also have the potential of preserving bio signature evidence of past life if life ever developed on the planet and flourished in this area."
Eberswalde Crater: "The outstanding characteristic of Eberswalde crater is that it has a delta formation like that formed by the Mississippi river," Zurek says. The delta is highly structured and layered, "meaning that there were many episodes of water flowing into the crater," he says. Those layers are the kind of formation that could preserve evidence of past life if that life had developed on the planet, Zurek says.