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, Inc. The paper is available free online.

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.

The results support the potential for rocks ejected on asteroidal impact to carry microorganisms capable of reseeding the Earth, according to Horneck and coworkers, from the Institute of Aerospace Medicine (Koeln, Germany), Humboldt University of Berlin, Heinrich-Heine University (Duesseldorf, Germany), Ernst-Mach Institute for Short-Term Dynamics (Freiberg, Germany, Open University (Milton Keynes, U.K.), the German Collectin of Microorganism and Cell Culturews (Braunschweig, Germany), the Russian Academy of Science (Moscow), and the Planetary Science Institute (Tucson, AZ).

"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."

Astrobiology is an authoritative peer-reviewed journal published bimonthly in print and online. The journal provides a forum for scientists seeking to advance our understanding of life's origins, evolution, distribution and destiny in the universe. A complete table of contents and a full text for this issue may be viewed online.

Astrobiology is the leading peer-reviewed journal in its field. To promote this developing field, the Journal has teamed up with The Astrobiology Web to highlight one outstanding paper per issue of Astrobiology. This paper is available free online and to visitors of The Astrobiology Web.

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• Tribute to Paul C. Lauterbur
• The Spontaneous Development of Biology from Chemistry
• Superluminous Supernovae: No Threat from _ Carinae
• Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-Like Host Planets: First Phase of Lithopanspermia Experimentally Tested Astrobiology
• Acetylene as Fast Food: Implications for Development of Life on Anoxic Primordial Earth and in the Outer Solar System
• Formaldehyde in the Far Outer Galaxy: Constraining the Outer Boundary of the Galactic Habitable Zone
• Control of Lunar and Martian Dust--Experimental Insights from Artificial and Natural Cyanobacterial and Algal Crusts in the Desert of Inner Mongolia, China
• Subsurface Filamentous Fabrics: An Evaluation of Origins Based on Morphological and Geochemical Criteria, with Implications for Exopaleontology
• Identification of Morphological Biosignatures in Martian Analogue Field Specimens Using In Situ Planetary Instrumentation
• Some Ecological Mechanisms to Generate Habitability in Planetary Subsurface Areas by Chemolithotrophic Communities: The Rio Tinto Subsurface Ecosystem as a Model System
• Implications of an Anthropic Model of Evolution for Emergence of Complex Life and Intelligence
• Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks