If early Mars was as barren and cold as it is today then the bombardment of the Red Planet some four billion years ago by comets and asteroids may have made its climate more conducive to life, according to a study.
The impacts would have produced regional hydrothermal systems on Mars similar to those in Yellowstone National Park, which today harbour chemically powered microbes, some of which can survive boiling in hot springs or inhabiting water acidic enough to dissolve iron nails, said study co-author Stephen Mojzsis from the University of Colorado at Boulder.
Scientists have long known there was once running water on Mars, as evidenced by ancient river valleys, deltas and parts of lake beds, Mojzsis added.
In addition to producing hydrothermal regions in portions of Mars' fractured and melted crust, a massive impact could have temporarily increased the planet's atmospheric pressure, periodically heating Mars up enough to "re-start" a dormant water cycle.
Published recently in the journal Earth and Planetary Science Letters, the study took into consideration temperatures beneath millions of individual craters on Mars.
The researchers used computer simulations to assess heating and cooling, as well as the effects of impacts on the planet from different angles and velocities.
They found the heating of ancient Mars caused by individual asteroid collisions would likely have lasted only a few million years before the Red Planet -- about one and one-half times the distance to the sun than Earth -- defaulted to today's cold and inhospitable conditions.
"None of the models we ran could keep Mars consistently warm over long periods," Mojzsis said.
While Mars is believed to have spent most of its history in a cold state, Earth was likely habitable over almost its entire existence.
"What really saved the day for Earth was its oceans," Mojzsis said. "In order to wipe out life here, the oceans would have had to have been boiled away. Those extreme conditions in that time period are beyond the realm of scientific possibility," he added.
Mojzsis said the next step would be to model similar bombardment on Mercury as well as Venus to better understand the evolution of the inner solar system and apply that knowledge to studies of planets around other stars.
