Comets and asteroids as large as West Virginia smacking into Mars some 4 billion years ago could have created a haven for life there not so long after the birth of the solar system.
The ancient impacts some 4 billion years ago could have melted subsurface ice on a cold and barren Mars, producing regional hydrothermal systems much like those in Yellowstone National Park that harbor extreme life today, says Professor Steve Mojzsis. The solar system is believed to be roughly 4.6 billion years ago.
Scientists have long known there was once running water on Mars, as evidenced by ancient river valleys, deltas and parts of lake beds, explains Mojzsis, a professor in geological sciences. In addition to creating hydrothermal fields, such massive impacts on Mars could have temporarily increased the planet’s atmospheric pressure, periodically heating the planet 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,” says Mojzsis. “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.”
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. Unlike Earth, which has been “resurfaced” time and again by erosion and plate tectonics, heavy cratering is still evident on Mercury, Earth’s moon and Mars, Mojzsis notes.
Published in Earth and Planetary Science Letters, the study was conducted by Mojzsis and Oleg Abramov, a researcher at the U.S. Geological Survey in Flagstaff, Arizona and a former CU-Boulder research scientist under Mojzsis.
Mojzsis and Abramov used the Janus supercomputer cluster at the University of Colorado Computing facility for some of the 3-D 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.
The study showed the heating of ancient Mars caused by a giant asteroid collision 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 – before defaulting to today’s cold and inhospitable conditions.
“None of the models we ran could keep Mars consistently warm over long periods,” said Mojzsis.
While Mars is believed to have spent most of its history in a cold state, Earth was likely habitable over almost its entire existence. A 2009 study by Mojzsis and Abramov showed that the Late Heavy Bombardment period in the inner solar system nearly 4 billion years ago did not have the firepower to extinguish potential early life on Earth and may have even given it a boost if it was present.
“What really saved the day for Earth was its oceans,” Mojzsis notes. “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.”
Studies of Mars provide us with valuable information about our own place in the solar system, explains 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.”
