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EVIDENCE of life on Mars may have already arrived on Earth, hidden inside white meteorites made of sedimentary rock. That’s the new hope, at least.

So far, all meteorites from Mars have been made of volcanic rock. But sedimentary rock, laid down in ancient Martian oceans, may be the best place to look for evidence of alien life, since water is a life-friendly environment.

To see if such sedimentary meteorites could even survive the trip to Earth, Frances Westall and colleagues at the European Space Agency’s STONE-6 project glued two sedimentary rocks containing fossils and other life signatures to the heat shield of an uncrewed Russian space capsule in orbit.

Over half of each 4-centimetre-wide rock melted during re-entry, but the traces of life were still detectable. Samples of living bacteria coated on each rock died, but their charred remains survived.

The quartz crust of each rock fused to a creamy white colour. So meteorite hunters, who usually search for dark rocks, should be looking for lighter shades, says Westall, who presented the results at the European Planetary Science Congress last week.

Astrobiology – Learn more in our out-of-this-world .