DNA Survives Re-Entry Into Earth’s Atmosphere
Double-stranded DNA molecules applied to the outside of a rocket payload have survived being blasted into space: they briefly entered near total vacuum and returned through the atmosphere. At the end of this, the molecules could still transfer genetic information.
Contrary to some misunderstandings, the Rosetta mission did not find DNA on Comet Churyumov-Gerasimenko 67P. It did however find organic molecules. This revived discussion of the possibility, known as “panspermia” that life is distributed around the galaxy through molecules on comets or asteroids.
One of the challenges to this idea has been the question of whether something as complex as DNA could survive the extreme heat generated when entering the atmosphere. Exposure to cosmic rays or solar radiation while unprotected by the atmosphere represents another challenge to the theory.
However, the concept is looking more credible after a team from the University of Zurich pipetted DNA onto the outside of the TEXUS-49 sounding rocket, and collected it again after re-entry. They found the DNA could be inserted into bacteria and connective tissue cells and still function.
Dr. Cora Thiel came up with the idea of the experiment while planning to use TEXUS-49’s payload to study how gene expression changes in human cells in zero gravity. She started thinking about the biosignatures, which she describes as “molecules that can prove the existence of past or present extraterrestrial life.”
The outside of the same rocket looked like a particularly tough test – DNA cocooned inside an asteroid might have a better chance of surviving than something on a rocket’s metallic surface.
Reporting in PLOS ONE, Thiel used DNA carrying a green fluorescent protein and an antibiotic resistance cassette and applied the material both on the front surface of the payload and in more protected spots at the bottom and in grooves where screws were inserted.
Gas temperatures at the front of the craft reached over 1000° C. Even inside, it got to 130° C. Some of the DNA had burned off, but 53% was recovered from the payload bottom and as much as 35% was intact enough to produce both fluorescent proteins and antibiotic resistance when inserted into E. coli. Control areas had no detectable DNA, eliminating the possibility of contamination after the return to Earth. Mutation rates were low.
Thiel and her co-authors note that the findings are important for future missions to other planets or moons. “For these missions, it is essential to know whether the detected biomarkers definitely originate from the analysed site or if they could be potential contamination from “stowaways” which traveled as hitchhikers on the spacecraft or analytical equipment,” they argue. Knowing just what DNA can survive will help future projects decide what scrubbing needs to be done before launch.
The flight was only 13 minutes long, so there was no time to see how the DNA stood up to the radiation in space, but the capacity to survive the heat of re-entry could reshape thinking.