News in Science

Asteroid impact pushes life underground

Target for ET? Scientists studying life deep below an asteroid impact crater in the United States have found tiny organisms thriving kilometres under the surface.

The work, reported in the journal Astrobiology suggests impact craters may be a good place to look for life on other planets.

Despite a large fraction of Earth's bio-mass being on or below the surface, the new study is the first to examine how asteroid impacts affect sub-surface ecosystems.

Scientists including Professor Charles Cockell, from the University of Edinburgh, examined drill samples taken from deep below the Chesapeake Bay impact crater in Virginia, United States.

Cockell and colleagues studied cores taken from as far as 1.76 kilometres below the 90 kilometre-wide structure.

They say heat and pressure generated by the asteroid's impact would have killed all life near ground zero.

But Cockell and colleagues found microbes are still unevenly spread through the core sample, suggesting the environment is still settling 35 million years after the impact.

The collision also generated faults and fractures reaching down to rocks deep below, providing a path for water and nutrients to seep in.

They claim the impact damage provided a refuge for microbes, sheltering them from the effects major climatic events such as global warming and ice ages.

Life on Mars?

"The deeply fractured areas around impact craters can provide a safe haven in which microbes can flourish for long periods of time," says Cockell.

"Our findings suggest that the subsurface of craters on Mars might be a promising place to search for evidence of life."

Dr Michael Burton, an astronomer with the Australian Centre for Astrobiology at the University of New South Wales, is surprised that studies of microbial life deep below impact craters had not been carried out before now.

"They're opening up the possibility of new areas of exploration, other places we have not looked at yet that need attention," says Burton.

"If this is the case under one asteroid impact crater, the thing now is to get samples from other impact craters and see whether similar sorts of signatures for microbial organisms are found deep under these as well."

Burton points out that Mars would have been subject to impacts just like Earth.

"Mars was also once covered with liquid water and a thick atmosphere in its early days", he says.

That makes Mars a target for future searches.

"Of course there's still the technical challenge of trying to dig almost two kilometres through the Martian crust," says Burton.