DNA 'surprise' for space scientists
DNA can survive re-entry into the atmosphere, raising the possibility of extraterrestrial life molecules arriving on Earth from space, research has shown.
The discovery came as a total surprise to scientists who attached small double strands of DNA to the outer casing of a rocket.
Despite temperatures soaring to more than 1,000 degrees Celsius during the short flight to sub-orbital space and back, much of the DNA emerged intact.
Up to 53% was recovered from the grooves in screw heads and more than a third remained fully functional.
The "plasmid" DNA carried genes for fluorescence and antibiotic resistance.
It was shown to function by conferring antibiotic resistance to bacteria, and driving a flourescent marker in nucleated cells.
Dr Cora Thiel, one of the scientists from the University of Zurich in Switzerland, said: "We were completely surprised to find so much intact and functionally active DNA."
Colleague Professor Oliver Ullrich, from the same university, said: "This study provides experimental evidence that the DNA's genetic information is essentially capable of surviving the extreme conditions of space and the re-entry into Earth's dense atmosphere."
Many scientists believe comets may have brought organic building blocks of life such as amino acids to the Earth early in its history.
But some go further and suggest that DNA - the essential molecule of life itself - could reach the Earth in meteoric dust, 100 tons of which hit the planet each day.
The TEXUS-49 mission launched from the European base of Esrange in Kiruna, northern Sweden, was originally intended to study the influence of gravity on the genes of human cells carried inside the rocket.
But scientists decided, in addition, to test the effects of space travel on DNA carried at three positions on the rocket's outer casing.
The research suggested that scientists conducting space missions to other planets needed to be careful about contamination, researchers said.
Prof Ullrich said: "The results show that it is by no means unlikely that, despite all the safety precautions, space ships could also carry terrestrial DNA to their landing site.
"We need to have this under control in the search for extraterrestrial life."
The research is reported in the online journal Public Library of Science ONE.