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747px-EntryOn March 29, 2011, a TEXUS-49 rocket took off from northern Sweden for a short trip into space and back through Earth’s sheltering blanket of atmosphere. This amazing feat of engineering has become surprisingly routine — we humans have gotten to the point where launching a vehicle into space to carry out an experiment or deliver a satellite into orbit no longer inspires awe and wonder. Sounding rockets are commonly used as sub-orbital research platforms. In this case, one of the experiments on the mission was a test of how well DNA molecules can survive the temperatures involved in plummeting back through Earth’s atmosphere. The results, published earlier this year in PLOS ONE, show that DNA is tough enough to make it through atmospheric re-entry after a quick jaunt in space.

The research team attached DNA samples to various locations on the outside of the rocket nine days before it launched. They added the DNA in liquid droplets and then dried them with hot air, leaving the DNA stuck to the surface. They then covered these spots with foil until just before the launch to make sure their carefully prepared DNA wouldn’t be accidentally rubbed off. The team placed DNA samples directly on the surface of the rocket, as well as in the grooves of screw heads and on the bottom of the payload.

To guard against contamination, the team used DNA which had been engineered to contain genes that cause cells to glow green and make bacteria resistant to an antibiotic. This allowed them to confirm that any DNA they recovered after the flight was from their original samples, since the genes for glowing green and overcoming antibiotics are unlikely to be on random DNA molecules that might contaminate their research.

During the 13-minute flight, the payload got as high as 268km above the Earth (convention says that “space” starts at 100km); the temperature on the payload’s surface was 128°C during re-entry, and the gas around it reached temperatures of over 1000°C. The scientists tried recovering DNA from the application sites immediately after the payload was recovered and took their samples back to the lab for tests. They were able to recover up to 53% of the DNA from some sites — the grooves on the screw heads — and smaller quantities from more exposed areas, such as the payload’s surface. When they tried introducing the DNA into bacteria or mouse cells, 35% of the original sample was still functional — that is, it was taken up by the cells and made them glow or become antibiotic resistant.

Why does it matter that DNA can survive the flight through Earth’s atmosphere? For adherents of the panspermia hypothesis, it provides evidence that Earth can be seeded with complex organic molecules like DNA and proteins from space, and that some of these molecules will still be functional when they hit the ground. However, another issue may be equally important — or perhaps more so — as we continue to expand our footprint in space. “It’s not only an issue from space to Earth, it’s also an issue from Earth to space and to other planets,” said the researchers in a press release. “Our findings made us a little bit worried about the probability of contaminating space crafts, landers and landing sites with DNA from Earth.”

Image credit
The picture is an artist’s rendition of the atmospheric re-entry of the Mars Exploration Rover. Produced by NASA, it is in the public domain.

Thiel CS, Tauber S, Schütte A, Schmitz B, Nuesse H, Moeller R, & Ullrich O (2014). Functional activity of plasmid DNA after entry into the atmosphere of Earth investigated by a new biomarker stability assay for ballistic spaceflight experiments. PloS one, 9 (11) PMID: 25426925