DNA hitching a ride on the outside of a rocket has survived the launch, space travel and atmospheric re-entry to remain usable upon return to Earth, according to a new study.
The findings reported in the journal PLOS ONE adds to a growing body of evidence showing how some life can survive the extreme radiation, vacuum, and temperatures of space, and still be viable once it finds a safe environment to flourish.
"We were totally surprised," say two of the study's authors, Professor Oliver Ullrich and Dr Cora Thiel, both from the University of Zurich.
"Originally, we designed this experiment as a technology test for biomarker stability during space flight and re-entry. We never expected to recover so many intact and functional active DNA."
The finding raises issues for both the possible contamination of Earth by life from space, and also the contamination of other planets by infected probes from Earth.
"Our findings made us a little bit worried about the probability of contaminating spacecrafts, landers and landing sites with DNA from Earth," say the scientists.
Just add DNA
The scientists tested the ability of DNA samples to withstand high g acceleration during rocket launch, a period of space flight, the extreme heat of atmospheric re-entry, and the impact of landing.
They attached artificial plasmid DNA carrying a fluorescent marker and an antibiotic resistance gene cassette, to the outside of a rocket launched on a short suborbital flight in March 2011. Plasmids are small, circular, double-stranded DNA molecules separate from a cell's chromosomal DNA.
The samples were placed directly on the outer surface of the spacecraft, as well as in the grooves of screw heads on one of the experimental modules, and on the bottom side of the payload.
The rocket was launched on the TEXUS-49 mission from the European Space and Sounding Rocket Range in Sweden on a 780 second flight to an altitude of 268 kilometres.
The probe reached a maximum acceleration rate of 13.5 g during launch and 17.6 g during re-entry, reaching temperatures of over 1000°C.
The authors examined the stability and integrity of the bio-samples immediately after the flight, looking at the degree of DNA degradation and fragmentation.
Much to their surprise, they found almost 53 per cent of the DNA samples survived the flight, and 35 per cent retained full biological function.
The authors found the best survivability occurred to samples placed in the grooves of the screw heads.
"This is rigorous research and interesting in terms of the transfer of viable biological material between solar system objects," says Professor Malcolm Walter of the Australian Centre for astrobiology sciences at the University of New South Wales, who was not involved in the study.
"This is a different and much more likely version of the panspermia hypothesis with rocks being blasted off somewhere like Mars by an asteroid impact. The rocks, which contain microbes deep inside them, float though space and eventually fall to the surface of a planet such as Earth.
"Over 30 Mars meteorites have so far been detected on Earth, so we know there's a traffic of meteoroids between the planets and potentially a mechanism for transferring microbial life between the planets."