An interesting new study, published in Earth and Planetary Science Letters, has suggested that life on early Mars may have been able to grab a foothold thanks to impacts from asteroids and comets.

Of course, we don’t yet have direct evidence that life on Mars ever existed, or still does. But we are pretty certain it was once a wet environment, with rivers and possibly even oceans strewn across the surface. And this latest research suggests the environment may have been more habitable than thought, thanks to a bombardment of objects periodically heating the Red Planet.

“This study shows the ancient bombardment of Mars by comets and asteroids would have been greatly beneficial to life there, if life was present,” lead author of the study Professor Stephen Mojzsis of the University of Colorado Boulder said in a statement. “But up to now we have no convincing evidence life ever existed there, so we don’t know if early Mars was a crucible of life or a haven for life.”

These impacts would have occurred during the Late Heavy Bombardment phase of the Solar System about 3.9 billion years ago, when we think numerous impacts occurred on multiple bodies. Evidence for this remains visible in the form of craters on unaltered bodies like the Moon.

The researchers think that objects as large as the state of West Virginia would have struck Mars. These collisions would have caused a temporary heating of the Martian atmosphere, turning what may have been a cold environment into one more welcoming to life.

The impacts would have heated Mars for just a few million years at a time, before the planet returned to the cold and barren conditions we see today. But this brief window would have produced hydrothermal regions similar to those seen near Yellowstone on Earth, where we know microbes exist, and perhaps also re-started dormant water cycles as subsurface ice melted. 

Conversely, similar impacts are thought to have occurred on Earth, but they were not large enough to ruin what was likely already a habitable environment. In fact, our oceans may have played a part in lessening the impact, allowing life to thrive. “In order to wipe out life here, the oceans would have had to have been boiled away,” said Mojzsis. “Those extreme conditions in that time period are beyond the realm of scientific possibility.”

Whether Mars went through similar periods of habitability remains an open question. But if it did, it raises the prospect that life, in even its most primitive form, may have been able to exist, or perhaps still does today underground. Future missions to the Red Planet, including ESA’s ExoMars rover and NASA’s as-yet unnamed Mars 2020 rover, will endeavor to answer this question once and for all.