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By Michael Marshall

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Every afternoon, microorganisms fly into the Atacama Desert on grains of dust carried by the wind. The wind-driven dust could be how microbes first colonised the desert.

If there are microbes alive on Mars, they could be carried around the planet by the regular world-spanning dust storms, just like the Atacama microbes, says Armando Azua-Bustos of the Centre of Astrobiology in Madrid, Spain.

The Atacama Desert in South America is one of the driest places on Earth, with soils so dry they resemble those on Mars. Despite the extreme conditions, some microorganisms survive even in the very driest regions.

“We always wondered how those species got there in the first place,” says Azua-Bustos. He and his colleagues suspected the microbes were carried on dust particles by afternoon winds that blow in from the Pacific Ocean to the west.

Everything is dust in the wind

To find out, they set out Petri dishes filled with nutrients in long lines stretching from the coast to the desert interior. Any microbes flying in would land in them and grow. The team also set out empty dishes for collecting DNA from microbes that did not grow.

“I didn’t expect much,” says Azua-Bustos. But they found 28 species of microorganism growing on the plates, and extracted DNA from several more.

The microbes came from near the coast. Azua-Bustos says such microbes may have been the first to colonise the Atacama. He highlights Oceanobacillus oncorhynchi, which lives in tidal pools. Because the pools dry out in the heat of the day, it can survive being dried out for hours – giving it a chance of surviving the Atacama.

Mars is prone to dust storms, so if there is any microbial life there it could be dispersed on the dust grains, Azua-Bustos says. Even if there is no life there now, there may have been when the planet was younger and wetter.

If life can be transported around Mars, any contamination from our space probes could spread rapidly. “If we do carry contaminants to Mars, they could easily be dispersed by the Martian wind, as we have seen in the Atacama,” says Azua-Bustos.

However, it is not clear if the dust transport into the Atacama will continue. In the last few years the desert has had unprecedented rainstorms, which may be due to climate change. “We don’t know the effect of these rains on this transport process and the continuous flow of life across the Atacama,” says Azua-Bustos.

Journal reference: Scientific Reports, DOI: 10.1038/s41598-019-47394-z