This Bacterium Survived 30,000 Atmospheres of Pressure - Then Kept Functioning

The concept has a name - lithopanspermia - and it asks whether life forms could survive being blasted off one planet by an asteroid impact and landing on another. Mars and Earth have exchanged rocks throughout their histories; Martian meteorites have been found on Earth. The physics is plausible. The biology has been the sticking point. Could any organism actually survive the violence of planetary ejection?

Johns Hopkins researchers Lily Zhao, K.T. Ramesh, and colleagues decided to test it directly. They chose Deinococcus radiodurans, a desert bacterium collected from the high-altitude Atacama Desert in Chile - a location chosen because its extreme dryness, cold temperatures, and intense radiation resemble conditions on Mars more closely than most habitats on Earth. The bacterium is already well-known for surviving high doses of ionizing radiation and complete desiccation. The question was whether it could also survive being thrown from a planet.

The Experiment: Shooting Bacteria with a Gas Gun

The team devised a mechanical analog of planetary ejection. They sandwiched bacteria between steel plates, then fired a projectile at the steel assembly using a compressed-gas gun - accelerating the projectile to speeds up to 300 miles per hour. The collision generated pressures ranging from 1 to 3 gigapascals. One gigapascal equals roughly 10,000 atmospheres; the pressure at the bottom of the Mariana Trench, 11 kilometers below the ocean surface, is about 0.1 gigapascal. Even the lowest pressure tested in these experiments exceeded ocean-floor conditions by more than tenfold.

After each shot, the researchers measured bacterial survival and examined gene expression in the survivors to assess what kind of damage had occurred and how cells were responding.

The bacteria proved resistant. At 1.4 gigapascals, they survived nearly every test run, showing no visible physical damage. At 2.4 gigapascals, survival dropped to 60 percent, and microscopic imaging revealed some ruptured membranes. Transcription profiles at that pressure showed cells were activating DNA repair pathways - the bacteria were not merely enduring the pressure passively, they were actively fixing the damage it caused.

"We expected it to be dead at that first pressure," said lead author Lily Zhao. "We started shooting it faster and faster. We kept trying to kill it, but it was really hard to kill."

Equipment Failed Before the Bacteria Did

The steel configuration holding the plates ultimately fell apart from the repeated stress before the researchers could push bacteria beyond 3 gigapascals. That hardware limit, not biological failure, ended the experiment. The bacterium's thick, layered cell envelope - a multi-membrane structure already known to provide radiation shielding - appears to distribute pressure in ways that protect the interior.

For context, estimates of the pressures experienced during actual ejection from Mars span a wide range, but some debris would experience pressures in the range tested. Material near the edge of an impact crater, or debris that reaches escape velocity through less direct paths, might experience pressures closer to the 1-to-3 gigapascal range tested here. Not all ejected material would survive, but some fraction could.

"We have shown that it is possible for life to survive large-scale impact and ejection," Zhao said. "What that means is that life can potentially move between planets."

Implications for Planetary Protection

The finding has direct implications for how space agencies approach missions to Mars and its moons. Current protocols focus heavily on preventing contamination of Mars with Earth organisms. But if life can move between planets via asteroid debris, then Phobos - Mars's inner moon, which orbits close enough to receive ejecta at relatively low velocities and pressures - might also warrant attention.

Material reaching Phobos from Mars would experience far lower pressures than material that travels all the way to Earth. If the bacterium can survive pressures well above those needed for Mars-to-Phobos transfer, then Phobos could theoretically harbor Martian life even if Mars itself does not currently show obvious signs of habitability.

"We might need to be very careful about which planets we visit," Ramesh said.

The study is published in PNAS Nexus and represents a single organism tested under a specific set of experimental conditions. The researchers did not simulate the full chain of interplanetary transfer - vacuum exposure, radiation during transit, and the heat and pressure of atmospheric entry on the receiving planet are all additional filters that life would have to survive. Whether D. radiodurans would clear all of those hurdles simultaneously remains to be tested. The team's next step is exploring whether repeated pressure exposure might actually select for more resistant bacterial populations over generations.