With Sunday's successful landing of the Mars Science Lab, the search for life has taken on a new sense of urgency. The Curiosity Science Mission goal is to look for chemical evidence of ancient life preserved within exposures near the base of a five-kilometers high mound of layered materials at the center of Gale crater. But the red planet says Robert Zubrin, founder of The Mars Society, is essentially a Rosetta stone for determining the prevalence and diversity of life in the universe.
Mars once boasted gravity, an atmosphere, and liquid water in great abundance. According to Zubrin, if life is indeed a natural, chemical development wherever liquid water, reasonable temperatures and various minerals occur, then why shouldn't it have appeared on Mars?
Evidence of possible life on Mars sent back from by two Mars Viking Landers in 1976 and 1977 was inconclusive, at least according the then primitive knowledge of both extreme life that we now know exists on Earth as well as the abundant existence of water and methane on Mars past and present.
On Mars, as on Earth, methane is extremely unstable because it's continually being broken up by ultraviolet rays from the Sun and chemical reactions with other gases. The average life of a methane molecule on Mars is 400 years, which means the gas must be continually replenished or it will disappear. Something is producing methane on Mars today -the big question is: What? There is potentially a vast biosphere a few meters below Mars' surface, which the Viking mission may not have been able to access since it was only scratching the surface of the uppermost layer of soil.
In fact, NASA's first press release about the Viking tests announced that the results were positive. The "labeled Release" (LR) experiments had given positive results. But after lengthy discussions in which Carl Sagan participated, NASA reversed its position, mainly because another experiment detected no organics in the soil.
Yet to this day, Gilbert Levin, the principal designer of the LR experiment, believes the tests pointed to life. When the same two experiments were run on soil from Antarctica, the same conflicting results were obtained (LR - positive; organics - negative.) Soil and ice from Antarctica's Dry Valley certainly contains extreme life forms. The test for organics was negative because it is far less sensitive than the LR experiment. The same problem could have caused the organics test on to give a false negative.
Before oxygen could accumulate in Earth's atmosphere, all the exposed iron had to rust. During that process, lasting hundreds of millions of years, Earth was also a red planet.
In the journal Nature, Corinna Wu has asked: Could the oxygen that rusted the iron on have been produced biologically? Could life on have simply "run out of steam" after that stage of its development?
Recent NASA and Mars Express images suggest that Mars was warm enough to sustain lakes and rivers three billion years ago, a period that was previously thought to be too cold and arid to sustain water on the surface.
Research by a team from Imperial College London and University College London (UCL), suggests that during the Hesperian Epoch, approximately 3 billion years ago, Mars had lakes made of melted ice, each around 20km wide, along parts of the equator.
Earlier research had suggested that Mars had a warm and wet early history but that between 4 billion and 3.8 billion years ago, before the Hesperian Epoch, the planet lost most of its atmosphere and became cold and dry.
In another study, the researchers analysed detailed images from NASA's Mars Reconnaissance Orbiter, which is currently circling the red planet, and concluded that there were later episodes where Mars experienced warm and wet periods.
The researchers used the images from the Mars Reconnaissance Orbiter to analyse several flat-floored depressions located above Ares Vallis, which is a giant gorge that runs 2,000 km across the equator of Mars. Scientists have previously been unable to explain how these depressions formed, but believed that the depressions may have been created by a process known as sublimation, where ice changes directly from its solid state into a gas without becoming liquid water. The loss of ice would have created cavities between the soil particles, which would have caused the ground to collapse into a depression.
The researchers analyzed the depressions and discovered a series of small sinuous channels that connected them together. The researchers say these channels could only be formed by running water, and not by ice turning directly into gas.
The scientists were able to lend further weight to their conclusions by comparing the Mars images to images of thermokarst landscapes that are found on Earth today, in places such as Siberia and Alaska. Thermokarst landscapes are areas where permafrost is melting, creating lakes that are interconnected by the same type of drainage channels found on Mars.
The team believe the melting ice would have created lakes (images at top of page) and that a rise in water levels may have caused some of the lakes to burst their banks, which enabled water to carve a pathway through the frozen ground from the higher lakes and drain into the lower lying lakes, creating permanent channels between them.
The researchers determined the age of the lakes by counting crater impacts, a method originally developed by NASA scientists to determine the age of geological features on the moon. More craters around a geological feature indicate that an area is older than a region with fewer meteorite impacts.
In the study, the scientists counted more than 35,000 crater impacts in the region around the lakes, and determined that the lakes formed approximately three billion years ago. The scientists are unsure how long the warm and wet periods lasted during the Hesperian epoch or how long the lakes sustained liquid water in them.
The researchers say their study may have implications for astrobiologists who are looking for evidence of life on Mars. The team say these lake beds indicate regions on the planet where it could have been warm and wet, potentially creating habitats that may have once been suitable for microbial life. The team say these areas may be good targets for future robotic missions.
It's entirely possible that Mars goes through periods of reawakening of its biosphere during spells when a surge of liquid surface water becomes available from heightened volcanic activity that pump vast quantities of greenhouses gases into the atmosphere and dormant cycles when lengthier cold and dry periods prevail as is the case on Mars today.
The Daily Galaxy via University College London and Discovery.com
Image Credit: NASA/JPL