* Astronomy

A class of especially hardy microbes that live in some of the harshest Earthly environments could flourish on cold Mars and other chilly planets, according to a research team of astronomers and microbiologists. In a two-year laboratory study, the researchers discovered that some cold-adapted microorganisms not only survived but reproduced at 30 degrees Fahrenheit, just below the freezing point of water. The microbes also developed a defence mechanism that protected them from cold temperatures. These close-up images, taken by an electron microscope, reveal the tiny one-cell organisms, called halophiles and methanogens, that were used in the study.


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New research suggests that dust devils and storms on Mars produce oxidants that would render the planet's surface uninhabitable for life as we know it.

"As a consequence, any nascent life (microorganisms, for example) or even prebiotic molecules would find it hard to get a foothold on the surface of Mars, as the organic material would be scavenged efficiently by the surface oxidants" - Sushil Atreya, University of Michigan professor in the Department of Atmospheric Oceanic and Space Sciences.

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A mysterious shiny coating found on rocks in many of Earth's arid environments could reveal whether there was once life on Mars, according to new research.

The research, published in the July edition of the journal Geology, reveals that the dark coating known as desert varnish creates a record of life around it, by binding traces of DNA, amino acids and other organic compounds to desert rocks. Samples of Martian desert varnish could therefore show whether there has been life on Mars at any stage over the last 4.5 billion years.
The researchers hope that these results will encourage any future Mars Sample Return mission to add desert varnish to its Martian shopping list.

The source of the varnish, which looks like it has been painted onto the rocks, has intrigued scientists since the mid nineteenth century, including Darwin, who was so fascinated that he asked the geochemist Berzelius to investigate it. It was previously suggested that its dark colour was the result of the presence of the mineral manganese oxide, and that any traces of life found within the varnish came from biological processes caused by microbes in this mineral.
However, the new research used a battery of techniques, including high resolution electron microscopy, to show that any traces of life in the varnish do not come from microbes in manganese oxide. The research reveals that the most important mineral in the varnish is silica, which means that biological processes are not significant in the varnish's formation. On desert rock surfaces, silica is dissolved from other minerals and then gels together to form a glaze, trapping organic traces from its surroundings.

Dr Randall Perry, lead author of the research from the Department of Earth Science and Engineering at Imperial College London, explained that as life is not involved in desert varnish formation, the varnish can act as an indicator of whether life was present or absent in the local environment.

"If silica exists in varnish-like coatings in Martian deserts or caves, then it may entomb ancient microbes or chemical signatures of previous life there, too. Desert varnish forms over tens of thousands of years and the deepest, oldest layers in the varnish may have formed in very different conditions to the shallowest, youngest layer. These lustrous chroniclers of the local surroundings can provide a window back in time. Martian desert varnish would contain a fascinating chronology of the Martian setting" - Dr Randall Perry.

The research was carried out by researchers at Imperial College and the Universities of Auckland (NZ); Wisconsin-Parkside and Washington (US); and Nottingham Trent (UK).

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Title: `Baking black opal in the desert sun: The importance of silica in desert varnish`
Authors: Perry, Randall S., Lynne, Bridget Y., Sephton, Mark A., Kolb, Vera M., Perry, Carole C., Staley, James T.
Journal: Geology

A University of California, Berkeley, study of methane-producing bacteria frozen at the bottom of Greenland's two-mile thick ice sheet could help guide scientists searching for similar bacterial life on Mars.

Methane is a greenhouse gas present in the atmospheres of both Earth and Mars. If a class of ancient microbes called Archaea are the source of Mars' methane, as some scientists have proposed, then unmanned probes to the Martian surface should look for them at depths where the temperature is about 10 degrees Celsius warmer than that found at the base of the Greenland ice sheet, according to University of California, Berkeley lead researcher P. Buford Price, a professor of physics.
This would be several hundred meters underground, where the temperature is slightly warmer than freezing and such microbes should average about one every cubic centimetre.
While Price is not expecting any time soon a mission to Mars to drill several hundred meters beneath the surface, methanogens (methane-generating Archaea) could just as easily be detected around meteor craters where rock has been thrown up from deep underground.

"Detecting this concentration of microbes is within the ability of state-of-the-art instruments, if they could be flown to Mars and if the lander could drop down at a place where Mars orbiters have found the methane concentration highest. There are oodles of craters on Mars from meteorites and small asteroids colliding with Mars and churning up material from a suitable depth, so if you looked around the rim of a crater and scooped up some dirt, you might find them if you land where the methane oozing out of the interior is highest." - P. Buford Price.

Price and his colleagues published their findings last week in the Early Online edition of the journal Proceedings of the National Academy of Sciences, and presented their results at last week's meeting of the American Geophysical Union in San Francisco.
Variations in methane concentration in ice cores, such as the 3,053-meter-long core obtained by the Greenland Ice Sheet Project 2, have been used to gauge past climate. In that core, however, some segments within about 100 meters of the bottom registered levels of methane as much as 10 times higher than would be expected from trends over the past 110,000 years.
Price and his colleagues showed in their paper that these anomalous peaks can be explained by the presence in the ice of methanogens. Methanogens are common on Earth in places devoid of oxygen, such as in the rumens of cows, and could easily have been scraped up by ice flowing over the swampy subglacial soil and incorporated into some of the bottom layers of ice.
Price and his colleagues found these methanogens in the same foot-thick segments of the core where the excess methane was measured in otherwise clear ice at depths 17, 35 and 100 meters above bedrock.
They calculated that the measured amount of Archaea, frozen and barely active, could have produced the observed amount of excess methane in the ice.

"We found methanogens at precisely those depths where excess methane had been found, and nowhere else. I think everyone would agree that this is a smoking gun"- P. Buford Price

Biologists at Pennsylvania State University had earlier analysed ice several meters above bedrock that was dark gray in appearance because of its high silt content, and identified dozens of types of both aerobic (oxygen-loving) and anaerobic (oxygen-phobic) microbes. They estimated that 80 percent of the microbes were still alive.
Though methane has been detected in Mars' atmosphere, ultraviolet light from the sun would have broken down the amount observed in about 300 years if some process was not replenishing the methane. While interaction of carbon-bearing fluid with basaltic rock might be responsible, methanogens might instead take in subsurface hydrogen and carbon dioxide to make the methane.
If methanogens are responsible, Price calculated that they would occur in a concentration of about one microbe per cubic centimetre at a depth of several hundred meters, where the temperature - about zero degrees Celsius or a bit warmer - would allow just enough metabolism for them to keep alive, just as the microbes in the Greenland ice sheet are doing.

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