Ice is a common feature of many of the worlds in the solar system with the potential to support life. Working out how to detect the signature of life - past or present - in ice will be a key part of solar system exploration. Project SLIce - Signatures of Life in Ice - is designed to find out both what signs of life might survive in ice, and how to detect it in a scientifically robust way.

At the Goldschmidt2009 meeting in Davos, Switzerland this week, Dominique Tobler and Jennifer Eigenbrode of NASA Goddard Space Science Laboratory, and Liane Benning of the University of Leeds, UK, show that not only living micro-organisms, but also traces of long-dead ones, and the food that sustained them can be detected in shallow ice layers, using methods rigorously tested in one of our own planet's most extreme environments.

"With SLIce, we wanted to figure out the nature of the organic matter in ice and how what we find on Earth can be the basis for comparisons with organic matter on Mars," explains Benning.

"The organic matter we find could be alive or dead, representing extant or extinct life, or even the nutrients that made life possible, and we want to identify the biological signals that point towards ice-dwelling life."

The SLIce team went to a glacial region of Svalbard to try taking ice samples in exactly the way it would be done on Mars, using a sequence of procedures and tests that they had developed as part of the AMASE project, a long-running international research program that has established Svalbard as a test bed for planetary exploration.

"We're using sample devices, primarily to be operated from a rover, but we're also testing how we go about taking and testing samples and keeping them separate," says Benning.

"For SLIce, we applied the protocol we had developed to take ice cores, process them and analyze them in the field just as would happen on a rover on Mars, and then of course we took them back to the lab and did a much wider range of tests, so we really knew what we had found. There could be microbes living in the ice, but there could also be the dead bodies of microbes that used to live there, and there could be biological molecules that blew in from dust and micrometeorites. We need to identify what we've got, so that we know what it's telling us."

One of the things that the Svalbard experiments told them was that the highest concentrations of living microbes were in ice layers close to the surface, where a rover would be able to sample more easily than at several meters depth, for example.

The protocols that SLIce has developed include issues such as cleaning the scoop that a rover would use to take samples, both before and after sampling, and between samples. This matters for the data - but also, potentially, for planetary security. "We want to be sure that the bugs we are measuring are Martian bugs and not something we brought with us on the spacecraft," says Benning.

"We were able to show that the methods that had been used to clean sampling tools in fact left them dirty. Although they made the scoop sterile, but that didn't mean it was clean. We found it was still dirty, and the dirt was dead micro-organisms. That's no good for what we want to do, as we want to find the dead bodies as well as anything alive. We now have ways of making tools not only sterile, but also organic-free to null levels. This is partly to make sure we don't spend all this time measuring material we brought from earth, but also as a form of forward planetary protection, including protection for Earth in the case of sample return missions.

"We went to Svalbard because it is a very good analogue for conditions on Mars," says Benning.

"The geology is the same as on Mars - it's the only place on Earth with rocks like the Martian meteorite ALH0084, which showed possible fossil micro-organisms. Svalbard's cold, it's inhospitable and there's very little food for micro-organisms, so they live at a very slow metabolic rate. If we hope to find the signatures of life in water-ice environments on Mars, then it's a good target. And thanks to the SLIce fieldwork, we know we have the techniques to get useful samples."

AMASE is a NASA-led project to test practical aspects of planetary exploration, and has established regions in Svalbard as a test-bed. This is one of the places NASA and ESA use to try our rovers and landers, and to troubleshoot techniques for doing fieldwork at a distance - between 56 and 400 million kilometers distance, in the case of Mars.

The aim is to ensure that rovers and instruments designed for future missions such as ESA's ExoMars, and NASA's Mars Science Laboratory, can cope with foreseeable problems.