Dreamers who see Mars as a habitable planet had to bake smaller and smaller rolls over time. While astronomers and philosophers in the 18th century still took intelligent Martians for granted, on the eve of the space age simple vegetation around the icy polar caps of Mars was at best conceivable. The first probes left only microbes as a possibility, and the first landing missions in 1976 did not even find traces of the organic molecules that should have existed on Mars even without biological activity, since comets and asteroids contain such things. As we know today, the UV light from the sun forms aggressive salts on the surface of Mars, which decompose everything organic.

Since then, hopes have rested on Mars paleontology. As it also turned out, there must have been rivers and lakes there three to four billion years ago, in whose deposits the third generation of Mars rovers is rummaging these days to find fossil traces of life under the corrosive surface. And so no new Mars mission will be launched that does not promise the discovery of evidence of life beyond the Earth's biosphere.

The study, which a team led by astrobiologist Armando Azua-Bustos has just published in "Nature Communications", now pretty much thwarts the hopeful PR poetry. The researchers had unleashed methods such as those used by current and planned Mars rovers to search for biomarkers on soil samples from the Chilean Atacama Desert. The samples come from an alluvial fan called "Red Stone" south of the city of Antofagasta, which is not only located in one of the driest regions on Earth, but also geologically very similar to the surface of Mars.

Laboratory tests showed that the samples contained small amounts of active and fossil soil microbes – but most of the analytical methods used on the rovers were virtually unable to detect their organic molecules. Of course, there were and still are many important scientific questions that new Mars probes are investigating. With a possible discovery of traces of life from Martian prehistoric times, however, it is better not to advertise a new mission that does not actually return samples for testing in laboratories on Earth.