Mashable discusses the discovery at Johns Hopkins of microbes that are hardy enough to have traveled across the vacuum of space and then survived the planet-breaking force of an asteroid impact. The hypothesis is called “lithopanspermia,” the idea that life travels between planets on chunks of space-rock. In other words, these tough little guys could be the “seeds” that brought life to Earth — or from Earth to other planets:
In a series of experiments at Johns Hopkins University, Lily Zhao fired tiny samples of a microorganism with a room-sized gas gun. The gun drove a steel plate into a thin, carefully prepared layer of bacteria at up to 2.4 gigapascals — tens of thousands of times Earth’s atmosphere at sea level. The purpose was to simulate the highest pressure a microorganism might face on its space journey: The initial launch.
Instead of total extermination, Zhao, a mechanical engineering doctoral student, found life — lots of it, in fact. After her initial test run, she cultured a regular sample, as well as the shocked sample so she could compare them side by side.
“I really didn’t know what to expect,” she told Mashable. “I was like, ‘Did I mislabel something or mix things up? Did I get the control and the shot sample confused?’ I was quite hesitant because it was such a high survival — like 95 or 97 percent survival.”
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Hopkins microbiologist Jocelyne DiRuggiero chose the superbug for the experiment. She selected Deinococcus radiodurans — or, “D. rad” — for its resistance to extreme radiation, dehydration, cold, and other factors. Those kinds of adaptations would be relevant for anything trying to persevere in space conditions. The so-called extremophile has even been found living in Chile’s Atacama Desert, one of the driest and most radiated places on Earth.
Earlier experiments by other groups had tried to test microbial survival from asteroid-like impacts, but the data were often sparse and hard to interpret, the researchers said. Some studies shot pellets containing microbes into sand or rock. But when a fraction survived, no one knew exactly what pressures those specific cells had experienced because their positions inside the target were unknown.
The Hopkins team set out to control that key variable. Zhao grew the cells in a liquid broth, then filtered them onto a thin membrane to create a uniform layer. She sandwiched that membrane between two ultra-flat steel plates, then used the gas gun to slam a third plate into the stack.
Machining and polishing the plates to the required flatness took weeks. On a firing day, Zhao spent eight to nine hours setting up the gun, then moved to a biology lab after each shot to put the shocked cells back into liquid culture and watch them regrow. A single experiment could take a few weeks of preparation for just a few microseconds of data.
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Among the surviving cells, some of their outer lining received damage, allowing DNA and proteins to get hurt. The cells temporarily dropped their normal routine — feeding, growing, and dividing — and switched into repair mode. Within a couple of hours, though, they had already begun to look like their old selves. The real surprise was in something basic: how the physical structure of a single cell could hold up under such violence in the first place.