Tiny life could spread across space in meteorites, experiment suggests

Scientists have discovered that a robust microbe can withstand pressures strong enough to pulverize rock, strengthening the hypothesis that life could survive the impact of a asteroid blow it off a planet.

In a series of experiments at Johns Hopkins University, Lily Zhao fired tiny samples of a microorganism with a coin-sized gas gun. The gun pressed a steel plate into a carefully prepared thin layer of bacteria at up to 2.4 gigapascals, or tens of thousands of times Earth’s atmosphere at sea level. The goal was to simulate the highest pressure a microorganism could face. space journey: the initial launch.

Instead of total extermination, Zhao, a doctoral student in mechanical engineering, found life – most of it, in fact. After her first test, she grew 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 thought, ‘Did I mislabel something or mix things up? Did I mix up the control and the shot sample?’ I was quite hesitant because the survival rate was very high – like 95 or 97 percent survival. »

THE researchfinanced by NASA and published in the journal Nexus PNASexamines a key element of the long-debated lithopanspermia hypothesis – the idea that extraterrestrial life could migrate between worlds enclosed in rocks broken off by asteroids or comets. Although no one knows if this happened, scientists have identified at least 400 meteorites on Earth from March.

Even at the highest pressure the installation could achieve before the steel hardware began to break, survival remained around 60%.

Zhao’s faculty director, KT Ramesh, said his interest in the issue arose from his involvement in a Study of National Academies who asked whether microbes could move from Mars to one of its nearby potato-shaped moons, Phobos.

NASA’s Perseverance rover on Mars captures an eclipse of Phobos crossing in front of the sun.
Credit: NASA/JPL-Caltech/ASU/MSSS/SSI

“We ended up saying that the probability was very low, but we also ended up saying that there wasn’t really any good data on which microbes could survive,” Ramesh, a professor of mechanical engineering, told Mashable. “So I thought, ‘Well, someone should get this data.'”

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. This type of adaptation would be relevant to anything attempting to persevere in spatial conditions. The so-called extremophile has even been found living in Chile’s Atacama Desert, one of the driest and most irradiated places on Earth.

Extremophiles and space

Previous experiments by other groups had attempted to test microbial survival following asteroid-like impacts, but the data were often sparse and difficult to interpret, the researchers said. Some studies have blasted microbe-containing pellets into sand or rocks. 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 decided to control this key variable. Zhao grew the cells in liquid broth, then filtered them through a thin membrane to create a uniform layer. She sandwiched this membrane between two ultra-flat steel plates, then used the gas gun to force a third plate into the stack.

Machining and polishing the plates to the required flatness took weeks. On a shooting day, Zhao spent eight to nine hours setting up the gun, then went to a biology lab after each shot to return the shocked cells to liquid culture and watch them grow back. A single experiment might require a few weeks of preparation for just a few microseconds of data.

DiRuggiero didn’t have high hopes for what would remain.

“I’m like, ‘There’s no way,'” she said of the plan. “‘Shoot a micro-organism? This thing will explode.'”

From a physical point of view, the pressures are extreme, even for non-living materials. Ramesh noted that water – which makes up a large part of any cell – begins to react strongly around two gigapascals, changing its volume and forming ices.

Working with detailed modeling, DiRuggiero realized that the most severe damage did not occur when cells were squeezed. The real problem came when the pressure suddenly dropped.

Microbe damage

Among the surviving cells, part of their outer wall was damaged, allowing DNA and proteins get hurt. The cells temporarily abandoned their normal routine – feeding, growing and dividing – and went into repair mode. Within a few hours, however, they had already started to look like themselves. The real surprise lay in something fundamental: how the physical structure of a single cell could withstand such violence in the first place.

Even at the highest pressure the experiment could achieve before the steel hardware began to fail, survival remained around 60 percent.
Credit: Lisa Orye / Johns Hopkins University Infographic

“I should know by now that microorganisms are absolutely amazing. They colonize every possible environment on Earth. We found them at the bottom of the ocean. We found them in Antarctic sea ice. We found them in acid mud pools,” DiRuggiero said. “If we find life elsewhere in the solar system – or outside the solar system – it will most likely be microorganisms.”

But for lithopanspermia to go from possible on paper to something that actually happens, life would have to survive much more than being ejected from its territory. An inhabited rock would have to withstand the deep freeze of space, drying out, space radiation, perhaps millions of years of travel, and then re-entry heat another world before landing. For years, Ramesh considered this chain of events to be incredibly remote odds.

Although the new results do not prove that life moves between planets and moons, it has changed the way he views this possibility.

“I went from saying, ‘It’s just extraordinarily unlikely, and we shouldn’t worry about it,’ to saying, ‘Well, OK, it’s possible,'” he said.

Planetary protection and contamination

Researchers have identified at least 400 Martian meteorites on Earth.
Credit: Tobias Roetsch / Future Publishing / Illustration Getty Images

The study also touches on a sensitive point in planetary protection: the effort to avoid accidentally seeding other planets with terrestrial life. Space agencies already clean the spaceship within reason before sending them on a mission, but there are almost always a few resilient parasites left.

Scientists are particularly wondering what this means for Mars. If bacteria, fungi or other microscopic life If we were to survive in a clean room on Earth, that doesn’t guarantee that these stragglers will actually grow up once they arrive on the red planet. But dead microbes still leave traces of DNA, which could complicate future attempts at discernment. a native Martian of our own contamination.

Planetary protection policies classify certain worlds as requiring strict starship cleanliness to avoid contamination. Results like these could influence which organisms space agencies deem vulnerable. Phobos, according to Ramesh, should probably be added to this list.

Meanwhile, the work highlights how difficult even a simple and tiny life can be. For Ramesh, who has been studying the mechanics of asteroid craters for more than 15 years, the results convinced him that new craters might actually be good places to look for life. The craters may have cracks allow water to flow through them.

“Maybe they’re not as good at sterilizing life as I thought,” he said.