DNA, the material that contains the code for life itself, can survive a trip through space and re-entry into Earth's atmosphere, all the while retaining its ability to transfer genetic information, researchers say.
A team of Swiss and German scientists applied fragments of DNA to the exterior surface of a sounding rocket before it blasted off for a low-orbit, 13-minute flight into space.
After the rocket landed, the double-stranded DNA molecules were still found in all the locations where they had been placed on the rocket, the team reported in the journal PLOS ONE.
The testing of DNA's survivability had not been on the researches' minds when they set up an experiment inside the rocket's science payload bay designed to analyze the effect of low gravity or even zero gravity on DNA and its functions.
It was during preparations for the flight that the researchers decided to also apply some DNA to some exterior locations of the TEXUS-49 rocket before its launch from a site in northern Sweden.
When they examined the externally applied DNA after the rocket's return to earth, they found as much as a third of it still functional and able to transfer genetic information to bacterial and connective tissue cells.
"We were totally surprised ...We never expected to recover so many intact and functional active DNA," said lead study author Cora Thiel, a molecular biologist at the University of Zurich. "Our findings made us a little bit worried about the probability of contaminating space crafts, landers and landing sites with DNA from Earth."
The DNA in the study was not chromosomal DNA, the type found in most living organisms including humans that passes on genetic coding information to new cells and to the organism's offspring.
Instead, the researchers were using plasmid DNA, a much smaller molecule present in some bacteria that works slightly differently from chromosomal DNA.
"We cannot say how these big chromosomal DNA molecules would react under the same conditions and this should be investigated in a separate experiment," said biochemist Oliver Ullrich of the University of Magdeburg in Germany. "However, we speculate that small plasmid DNA molecules might be more resistant to re-entry conditions than chromosomal DNA, which is also packed with proteins."
The experiment joins a number of others in which the robustness and possible survival of life in outer space has been investigated, with bacteria and some other small organisms subjected to the extreme condition they would encounter in outer space.
Many scientists have wondered whether life can be spread to planets throughout the cosmos on comets, asteroids or meteors.
The recent study isn't conclusive evidence that life, or even just DNA, might survive an extended voyage through space, so Ullrich cautions against reading too much into it.
"It is only a very, very small step for a very big question," he said.
