If there is life on Mars, it is probably underground—where our rovers can’t see it

Apart from finding mundane facts about Mars, one of NASA’s Curiosity rover’s tasks is to search for life on the red planet. But new research suggests that, if there is indeed life on Mars, our rovers may not be able to see it.

So far, the Curiosity rover has only drilled about 3 inches (7.6 cm) into Mars’ soil, and found nothing. According to an analysis of Martian meteorites found on Earth, signs of life on Mars are more likely to be found deep underground, rather than on or near the surface.

There have been more than 100 meteorites to land on Earth from Mars that scientists know of. Meteorites are chunks of rock from Mars that got knocked off of the surface when an asteroid or comet hit the planet. Sometimes they get pulled into Earth’s gravity and fall to the ground.

The new research, published in Nature Communications, crushed meteorites from Mars found on Earth and found out they released methane, one of the indicators of life. “The availability of methane and hydrogen is critical to the potential of the Martian crust as a habitat for microbial life,” according to a research team led by Nigel Blamey of Brock University. “Any life on Mars is likely to be in the subsurface.”

More than 90% of the methane produced on Earth comes from organic life—humans, plants, insects, and animals (especially cows). But non-living sources of methane have also been known to support bacteria.

Scientists are still divided about what the presence of methane on Mars means. It could support the existence of methane-feeding bacteria, or it could suggest the existence of methane-producing organisms that lived on Mars millions of years ago, when liquid water may have flowed on on its surface. But the methane in the meteorites found by Blamey and his team was most likely formed by chemical reactions between volcanic rocks and the Martian atmosphere.

“In essence the research confirms that an energy source for microbial activity exists in the Martian environment but in the subsurface,” Blamey told Quartz. “We do not have evidence of life, only that there is an available food source in the subsurface that potential microbial life could metabolize.”

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