PARIS, Jan 9: The theory that meteorites carrying bacteria kickstarted life on Earth has been strengthened by a German experiment that placed bugs in orbit to see if they survived the brutal environment of space.

The Swedish chemist Svante Arrhenius proposed the theory in 1903, contending that billions of years ago, bacteria drifting through the cosmos landed in the fertile soil of Earth, where they flourished and evolved into higher forms of life.

Critics of Arrhenius’s so-called pan-spermia theory say that unprotected bacterial hitchhikers would have been slaughtered by cosmic rays and ultraviolet radiation from the Sun.

The argument has raged back and forth, spiced by contemporary research into rocks that were knocked off the surface of Mars, presumably by some asteroidal collision, and eventually landed on Earth as meteorites.

Some scientists suggest that these meteorites once harboured bacterial spores, although the evidence is strongly opposed by others.

Seeking to check this, a team led by Gerda Horneck of the German Aerospace Centre in Cologne, sent bacteria into space in a series of remote-controlled experiments aboard Russian Foton satellites in 1994, 1997 and 1999.

Their research, published in December’s issue of a specialist Dutch-based journal, Origins of Life and Evolution of the Biosphere, provides powerful backing for the panspermia lobby.

The experiment entailed exposing nearly 50 million unprotected spores of a common soil bug, Bacillus subtilis, outside the satellite — the first time any living organism has been purposely exposed to space. The experiment would have been banned on a human mission, but was possible on an unmanned one.

After liftoff, the lid of a container holding the bugs was opened, to expose the sample to space for 10 to 15 days of the two-to-three-week mission.

On the first trip, UV radiation from the Sun killed nearly all the spores, confirming Arrhenius’ critics in their belief that single bacteria would not have survived long enough in space to travel from one planet to another.

On the second trip, the spore batch was confined under quartz, with the same outcome.

On the third trip, the batch was mixed with particles of clay, red sandstone, Martian meteorite or simulated Martian soil, to make small lumps a centimetre across, the idea being to simulate a mineral shield for the bugs.

In most of the samples, between 10,000 and 100,000 spores of the 50 million survived. The highest survival rate was with red sandstone sample, for nearly all the spores returned unscathed from space.

That supports the idea that bacteria from Mars or some other planet could have survived a relatively short trip to Earth, even if they were encased in only a small rock, Horneck suggests.

“Bacterial spores can be protected against solar UV radiation, if imbedded in clay or rock material in a ratio soil/spores comparable to that normally observed in terrestrial soils,” Horneck’s team writes.

“However, single spores or spores attached to micron-sized grains... will not survive in space.”

The experiment was conducted under a European Space Agency (ESA) programme called BIOPAN. The British weekly New Scientist reports on the research in next Saturday’s issue.—AFP