Berlin, September 25 : An artificial meteorite designed by the European Space Agency (ESA) has shown that traces of life in a Martian meteorite could survive the violent heat and shock of entry into the Earth's atmosphere.
The experiment's results also suggest that meteorite hunters should widen their search to include white rocks if they want to find traces of life in Martian meteorites.
The STONE-6 experiment tested whether sedimentary rock samples could withstand the extreme conditions during a descent though the Earth's atmosphere where temperatures reached at least 1700 degrees Celsius.
After landing, the samples were transported in protective holders to a laboratory clean-room at ESTEC (European Space Research and Technology Centre) and examined to see if any traces of life remained.
Recent missions have gathered compelling evidence for water and sediments on early Mars. Potential traces of Martian life are more likely to be found in sediments that have been formed in water.
However, although about 39 known meteorites from Mars have been identified, all are basaltic rock-types and no sedimentary meteorites have been found to date.
According to Dr Westall, "The STONE-6 experiment shows that sedimentary martian meteorites could reach Earth. The fact that we haven't found any to date could mean that we need to change the way we hunt for meteorites."
"In this experiment, we found that the sedimentary rocks developed a white crust or none at all. That means that we need to expand our search to white or light-coloured rocks," he added.
The STONE-6 experiment was mounted on a FOTON M3 capsule that was launched from Baikonur on 14th September 2007.
Two samples of terrestrial sedimentary rock and a control sample of basalt were fixed to the heat-shield of the return capsule, which re-entered the atmosphere on 26th September after 12 days in orbit.
The basalt was lost during re-entry.
However, a sample of 3.5 billion year old volcanic sand containing carbonaceous microfossils and a 370 million year sample of mudstone from the Orkney Islands containing chemical biomarkers both survived.
On examination at ESTEC, the 3.5 billion year old sample of sand from Pilbara in Australia was found to have formed a half-millimetre thick fusion crust that was creamy white in colour.
About half the rock had ablated but the microfossils and carbon survived at depth in the sample. Approximately 30 percent of the other sediment, a lacustrine sand from the Orkney Islands, also survived, as did some of the biomolecules.
The rocks also transported living organisms, a type of bacteria called Chroococcidiopsis, on the back of the rocks, away from the exposed edge.
"The STONE-6 experiment suggests that, if Martian sedimentary meteorites carry traces of past life, these traces could be safely transported to Earth," said Dr Westall.