Comets and asteroids allowed Mars to host life, study finds

Even if Mars was as cold and barren in the ancient past as it is now, it was likely made habitable following a barrage of asteroids and comets that took place four billion years ago, according to a new paper published this week in the journal Earth and Planetary Science Letters (EPSL).

The study, which was led by researchers at the University of Colorado-Boulder, explained that a bombardment such as this would have produced enough heat to melt subsurface ice, producing a number of regional hydrothermal systems capable of sustaining chemically-powered microbes.

These systems would be similar to those currently found in Yellowstone National Park, the study authors explained, and the microbes they support are hardy enough to live in the boiling water of a hot spring or H2O containing enough acid to dissolve nails. It would also help explain evidence of running water found on the Red Planet in the form of ancient river valleys and lake beds.

As Stephen Mojzsis, a professor of geology and geochemistry at the university, and his fellow researchers explained in a statement, massive impacts from comets and asteroids likely would have also caused the planet’s atmospheric pressure to increase temporarily, which in turn would cause its climate to heat up enough for its dormant water cycle to be re-ignited.

Impacts could not keep the Red Planet consistently warm, however

“This study shows the ancient bombardment of Mars by comets and asteroids would have been greatly beneficial to life there, if life was present,” the professor said. “But up to now we have no convincing evidence life ever existed there, so we don’t know if early Mars was a haven for life.”

The majority of this activity would have taken place during the period known as the Late Heavy Bombardment, approximately 3.9 billon years ago. While the Earth’s surface has been reshaped by erosion and plate tectonics on multiple occasions since then, Mars, Mercury and the moon still have craters showing the scars of asteroid and comet impact from this era, they said.

Using the university’s Janus supercomputer cluster, Mojzsis and his colleagues created three-dimensional models of the planet to investigate the temperatures below millions of individual craters to analyze heating and cooling. They also studied the results of impacts on the planet’s surface from impacts from various different angles and objects traveling at different speeds.

Their simulations revealed that the ancient Mars would have been heated by asteroid collisions just a few million years before the planet returned to the cold, inhospitable conditions found on the Red Planet today. None of the models were able to keep it warm over a prolonged period of time, Mojzsis said – a sharp contrast to Earth, which research has found has likely been habitable over its entire lifespan, thanks largely to its oceans.

“Studies of Mars provide us with valuable information about our own place in the solar system,” said Mojzsis. “Our next steps are to model similar bombardment on Mercury and Venus to better understand the evolution of the inner solar system and apply that knowledge to studies of planets around other stars.”

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Image credit: NASA