In the event that an asteroid or comet would impact Earth and send rock fragments containing embedded microorganisms into space, at least some of those organisms might survive and reseed on Earth or another planetary surface able to support life, according to a study published in the Spring 2008 (Volume 8, Number 1) issue of Astrobiology, a peer-reviewed journal published by Mary Ann Liebert.

In the report entitled, "Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-like Host Planets: First Phase of Lithopanspermia Experimentally Tested", Gerda Horneck and colleagues describe systematic shock recovery experiments designed to simulate a scenario called lithopanspermia, in which microorganisms are transported between planets via meteorites.

The first step of lithopanspermia would involve ejection of the microorganism-containing rock from the host planet as a result of an impact event.

The researchers sandwiched dry layers of three kinds of biological test systems, including bacterial endospores, endolithic cyanobacteria, and epilithic lichens, between gabbro discs, which are analogous to martian rocks. They then simulated the shock pressures martian meteorites experienced when they were ejected from Mars and determined the ability of the organisms to survive the harsh conditions.

The organisms selected represent "potential 'hitchhikers' within impact-ejected rocks," explain the authors, and are hardy examples of microbes that can withstand extreme environmental stress conditions, write the authors.

"Given that impacts have occurred on planetary bodies throughout the history of our solar system," says journal Editor, Sherry L. Cady, PhD, Associate Professor in the Department of Geology at Portland State University, "the hypothesis that life in rock could have been transferred between planets at different times during the past 3.5 billion years is plausible.

These experiments advance our understanding of the constraints on life's ability to survive the magnitude of impact that would accompany a meteoric trip from Mars to Earth."