The bombardment of the Red Planet about 4 billion years ago (Noachian period) by giant comets and asteroids likely enhanced climate conditions enough to make the planet more conducive to life, at least for a time, according to a new study that will be published in the May 15 issue of the journal Earth and Planetary Science Letters.

“If early Mars was as barren and cold as it is today, massive asteroid and comet impacts would have produced enough heat to melt subsurface ice,” explained study co-author Prof. Stephen Mojzsis, from the University of Colorado Boulder.

“The impacts would have produced regional hydrothermal systems on Mars similar to those in Yellowstone National Park, which today harbor chemically powered microbes, some of which can survive boiling in hot springs or inhabiting water acidic enough to dissolve nails.”

Planetary researchers have long known there was once running water on Mars, as evidenced by ancient river valleys, deltas and parts of lake beds.

In addition to producing hydrothermal regions in portions of the planet’s fractured and melted crust, a massive impact could have temporarily increased the atmospheric pressure, periodically heating Mars up enough to ‘re-start’ a dormant water cycle.

“This study shows the ancient bombardment of Mars by comets and asteroids would have been greatly beneficial to life there, if life was present. 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,” Prof. Mojzsis said.

Much of the action on Mars occurred during a period known as the Late Heavy Bombardment about 3.9 billion years ago when the developing Solar System was a shooting gallery of comets, asteroids, moons and planets.

Prof. Mojzsis said: “heavy cratering is still evident on Mercury, the Moon and Mars.”

Prof. Mojzsis and his colleague, Dr. Oleg Abramov from the U.S. Geological Survey, used the Janus supercomputer cluster at the University of Colorado for some of the 3D modeling used in the study.

They looked at temperatures beneath millions of individual craters in their computer simulations to assess heating and cooling, as well as the effects of impacts on Mars from different angles and velocities.

“A single model comprising the whole surface of Mars took up to two weeks to run on the supercomputer cluster,” Prof. Mojzsis said.

The study showed the heating of ancient Mars caused by individual asteroid collisions would likely have lasted only a few million years before the planet defaulted to today’s cold and inhospitable conditions.

“None of the models we ran could keep Mars consistently warm over long periods,” Prof. Mojzsis said.

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Oleg Abramov & Stephen J. Mojzsis. 2016. Thermal effects of impact bombardments on Noachian Mars. Earth and Planetary Science Letters, vol. 442, pp. 108-120; doi: 10.1016/j.epsl.2016.02.035