sábado, 26 de mayo de 2012

Searching Earth for Clues to What Mar's Curosity Rover Might Find

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Carl Sagan made a point of saying that "extraordinary claims require extraordinary evidence." If life ever existed on Mars, evidence of its presence may be signaled by a distinctive magnetic signature as a definitive test for Martian life that the Mars' Curosity rover could detect after its landing the evening of Aug. 5, 2012, PDT (early Aug. 6, EDT and Universal Time), according to a 2011 study led by Victoria Petryshyn of the University of Southern California. 

A mission to hunt for fossils remnants of eraly life on the Red Planet could  search for deposits of magnetite or other iron-bearing minerals in Martian sediment mounds similar to communities of micro-organisms on Earth that build large sedimentary mounds called microbialites (see below). The microbes clump together in slimy mats or films, which grow layer by layer as the microbes reproduce, creating microbialites. 
The most dramatic example of these mounds are stromatolites (image above, discovery, below), which form in shallow water and preserve a fossil record of life on Earth that stretches back 3.5 billion years. An "even" smattering of magnetic grains throughout such mounds would be strong evidence of long-ago capture by sticky microbial "biofilms." Microbes, however,  don't fossilize well, so the Curiosity rover might not find anything in a sample even if the mound once throbbed with bacteria.
The researchers harvested microbial mat samples from southern California to see if magnetite accumulation could serve as a "biosignature," placing the samples into a water-filled tank and inclined them at a variety of angles — from 0 degrees (horizontal) to 90 degrees (vertical). Then they introduced magnetite particles. They did the same thing with the mat samples swapped out for a carbonate control (microbialites generally contain a lot of carbonate minerals).
The team found that the mat samples trapped much more magnetite than the control, where magnetite particles concentrated at the bottom, as expected because of gravity. But the mat grabbed lots of magnetite across its entire surface, displaying how sticky biofilms are. Even vertically tilted mat samples snagged a lot of magnetite, while the stuff slid right off tilted control samples.
In conclusion, the team's experiments suggest that a future Mars' rover mission could search stromatolite-like mounds for magnetite or other iron-bearing minerals, Petryshyn said. Any mounds that exhibit lots of these minerals throughout their structure — not just at the bottom — were likely built by microbes.
"If we found a stromatolite-like structure on Mars, then the fight would begin," Petryshyn said.
A new Antarctic discovery could  help scientists better understand the conditions under which the both Earth's and Mars' planet's primitive life-forms thrived. “It’s like going back to early Earth,” says Dawn Sumner, a geobiologist at the University of California, Davis, describing her explorations of the eerie depths of East Antarctica’s Lake Untersee where Sumner and her colleagues, led by Dale Andersen of the SETI Institute in Mountain View, Calif., discovered otherworldly mounds of Photosynthetic microbial stromatolites.

The stromatolites, built layer by layer by bacteria on the lake bottom, resemble similar structures that first appeared billions of years ago and remain in fossil form as one of the oldest widespread records of ancient life dating from 3 billion years ago or more, to understand how life got a foothold on Earth. 
The purple-bluish mounds are composed of long, stringy cyanobacteria, ancient photosynthetic organisms. Similar to coral reef organisms, the bacteria takes decades to build each layer in Untersee’s icy waters, so the mounds may have taken thousands of years to accumulate.

Today, stromatolites are found in only a few spots in the ocean, including off the western coast of Australia and in the Bahamas. They they have also been found thriving in freshwater environments, such as super-salty lakes high in the Andes and in a few of Antarctica’s other freshwater lakes.
But scientists the size and shape of the purplish stromatolite mounds built by Phormidium bacteria in Untersee's extremely alkaline waters and high concentrations of dissolved methane, are unique reaching up to half a meter high, dotting the lake floor. “It totally blew us away,” Andersen said. “We had never seen anything like that.”
The ghostly blue stromatolite mounds were found adjacent to smaller, pinnacle-shaped lumps made of another bacterial group, Leptolyngbya.
“Everywhere else that we’ve looked you have a gradation between the structures,” like in bacterial mats sprawling around Yellowstone’s hot springs, she says. “There’s something very special about this particular example that’s allowing these large conical stromatolites to form.”
Andersen’s team has also studied Lake Vanda, which has a more transparent ice cover that lets more light penetrate, and Lake Joyce, with its thicker ice, which constrains how far down photosynthesizing organisms can grow, without finding large conical stromatolites there.
NASA's Mars Science Laboratory spacecraft is now more than halfway to Mars, with delivery of the one-ton rover Curiosity to the base of Mars' Gale Crater.
Recent tests completed aboard Curiosity confirmed all's well with science instruments the mission will use to learn whether an area holding an extensive record of Martian environmental history has ever offered conditions favorable for microbial life.
Because of its history, 96-mile wide Gale Crater crater with its strangely sculpted mountain --three times higher than the Grand Canyon is deep--is the ideal place for Curiosity to conduct its mission of exploration into the Red Planet's past. Researchers plan to use Curiosity to study layers in the mountain that hold evidence about wet environments of early Mars. Joy Crisp, MSL Deputy Project Scientist from NASA's Jet Propulsion Laboratory, explains:
"This may be one of the thickest exposed sections of layered sedimentary rocks in the solar system. The rock record preserved in those layers holds stories that are billions of years old -- stories about whether, when, and for how long Mars might have been habitable."
An instrument on Curiosity can check for any water that might be bound into shallow underground minerals along the rover's path. 
"If we conclude that there is something unusual in the subsurface at a particular spot, we could suggest more analysis of the spot using the capabilities of other instruments," said this instrument's principal investigator, Igor Mitrofanov of the Space Research Institute, Russia.
Today the Red Planet is a radiation-drenched, bitterly cold, bleak world. Enormous dust storms explode across the barren landscape and darken Martian skies for months at a time. But data from the Mars Reconnaissance Orbiter suggest that Mars once hosted vast lakes and flowing rivers.
"Gale Crater and its mountain will tell this intriguing story," says Matthew Golombek, Mars Exploration Program Landing Site Scientist from JPL. "The layers there chronicle Mars' environmental history."
In the gentle slopes around the mountain, Curiosity will prospect for organic molecules, the chemical building blocks of life. Mars Reconnaissance Orbiter has found an intriguing signature of clay near the bottom of the mountain and sulfate minerals a little higher up. Both minerals are formed in the presence of water, which increases potential for life-friendly environments.
One of Curiosity's 10 science instruments, the Radiation Assessment Detector (RAD) has been collecting data for three months, monitoring the natural radiation environment in interplanetary space. This information, particularly effects RAD has measured from recent solar flares, is crucial for design of human missions to Mars.

The descent from the top of Mars' atmosphere to the surface will employ bold techniques enabling use of a smaller target area and larger landed payload than were possible for any previous Mars mission. These innovations, if successful, will place a well-equipped mobile laboratory into a locale especially well suited for its mission of learning. The same innovations advance NASA toward capabilities needed for human missions to Mars.


Source: The Daily Galaxy - JPL/NASAspace.com, and astrobiology.com 

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