Ancient Mars May Have Been Teeming With Life

Ancient Mars may have had the right environmental conditions to support a subterranean world filled with microscopic organisms, researchers say. These microbes are known to thrive in extreme conditions on earth.

Scientists at the University of Arizona determined that if primary life forms did ever exist on Mars, they would have drastically altered the planet’s atmosphere, resulting in an ice age that would have led to their own extinction.

The study, which was published in the journal Nature Astronomy, analyzed the habitability of Mars around 4 billion years ago. Lead author Boris Sauterey and his team used climate and terrain models to simulate the temperatures at the surface and crust of the red planet.

“This allowed us to evaluate how plausible a Martian underground biosphere would be. And if such a biosphere existed, how it would have modified the chemistry of the Martian crust, and how these processes in the crust would have affected the chemical composition of the atmosphere.”

At the time, the planet is believed to have had a much denser atmosphere, rich in carbon dioxide and hydrogen. The temperate climate would have likely led to a planet teeming with water, capable of better sustaining life than it is today.

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The areas that were free of ice could have housed these organisms in a manner similar to early earth. Methanogens, known to exist in low-oxygen, extreme temperature and high-pressure conditions on earth, may have thrived underneath a thick layer of dirt protecting them from incoming radiation.

The atmosphere would have been thrown off kilter with the amount of hydrogen consumed from its carbon-dioxide-rich atmosphere, causing temperatures to drop by nearly 400 degrees Fahrenheit. The atmosphere “would have been completely changed by biological activity very rapidly, within a few tens or hundreds of thousands of years,” Sauterey said.

The microorganisms living near the surface would have burrowed deeper into the crust in an effort to survive the rapidly dropping temperatures.

“The problem these microbes would have then faced is that Mars’ atmosphere basically disappeared, completely thinned, so their energy source would have vanished, and they would have had to find an alternate source of energy. In addition to that, the temperature would have dropped significantly, and they would have had to go much deeper into the crust. For the moment, it is very difficult to say how long Mars would have remained habitable.”

This evolution of the atmosphere would have been different from earth, where microbes helped maintain the proper temperatures in an atmosphere dominated by nitrogen.

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Kaveh Pahlevan of the SETI Institute led another study that suggested Mars had warm oceans that persisted through millions of years. The hydrogen-dense atmosphere would have served as a greenhouse gas, trapping heat. Much of the hydrogen would eventually rise and dissipate into the atmosphere.

“This finding is significant because H2 is known to be a strong greenhouse gas in dense environments. This dense atmosphere would have produced a strong greenhouse effect, allowing very early warm-to-hot water oceans to stabilize the Martian surface for millions of years until the H2 was gradually lost to space. For this reason, we infer that—at a time before the earth itself had formed—Mars was born wet.”

The University of Arizona study analyzed the influence microbes had on Mars’ atmosphere during a different period when it was primarily dominated by carbon dioxide.

Pahlevan added in an email to The Guardian, “what their study makes clear, however, is that if life were present on Mars” during this earlier period, “they would have had a major influence on the prevailing climate.”

Future exploration projects on Mars may provide a clearer picture of potential life on early Mars. Researchers identified Hellas Planitia, a plain formed by the impact of a giant asteroid early in Mars’ history, as a site for possible evidence. However, the plain is home to some of the planet’s strongest dust storms, making it too challenging to be explored by autonomous rovers right now.