A new study from Johns Hopkins University indicates that microorganisms embedded in debris from asteroid impacts could potentially travel to other planets, including Earth, and survive.
The research demonstrates that a resilient bacterium, Deinococcus radiodurans, can withstand extreme pressure comparable to an ejection from Mars following an asteroid strike, as well as the harsh conditions of subsequent interplanetary journeys.
Published in PNAS Nexus, the study suggests that microorganisms can survive more extreme conditions than previously understood. This has significant implications for theories regarding the origins of life, planetary protection, and future space missions.
"The findings suggest life might survive ejection from one planet and migration to another, impacting perceptions of how life began on Earth." - K.T. Ramesh, Senior Author
The Lithopanspermia Hypothesis
Impact craters are common across the solar system, with Mars being heavily cratered. Martian meteorites found on Earth confirm that asteroid strikes can launch material into space. Scientists have long theorized whether life forms could also be launched from such impacts, a concept known as the lithopanspermia hypothesis.
Previous experiments on this theory have been inconclusive.
A Resilient Microbe Put to the Test
To test how a microorganism would realistically cope with planetary ejection stress, the team replicated the pressure using Deinococcus radiodurans. This desert bacterium is known for its remarkable resilience to extreme cold, dryness, intense radiation, and its ability to self-repair. Researchers noted that if life exists on Mars, it might possess similar capabilities.
The experiment simulated asteroid strike and ejection pressure by sandwiching the bacteria between metal plates and firing a projectile at them from a gas gun at speeds up to 300 mph. This generated pressures ranging from 1 to 3 Gigapascals (GPa), significantly higher than the pressure at the bottom of the Mariana Trench (0.1 GPa).
Remarkable Survival Rates
Following the simulations, the team assessed bacterial survival and examined their genetic material. The bacteria showed substantial resistance, surviving nearly all tests at 1.4 Gigapascals and 60% at 2.4 Gigapascals. While no damage was observed at lower pressures, higher pressure experiments resulted in some ruptured membranes and internal damage.
Lily Zhao, lead author, commented on the difficulty of destroying the bacteria.
"The equipment failed before the bacteria did." - Lily Zhao, Lead Author
Asteroid impacts on Mars can generate pressures up to approximately 5 Gigapascals. The microbe's survival at almost 3 Gigapascals exceeds previous expectations.
Zhao stated that the study demonstrates the possibility of life surviving large-scale impact and ejection, suggesting life's potential movement between planets.
Redrawing Planetary Protection Guidelines
The potential for life to spread between planetary bodies has significant implications for planetary protection and space mission protocols. Current guidelines assess the likelihood of life surviving on target planets and implement measures to prevent contamination.
The study's findings suggest that Martian material, potentially carrying life, could reach other bodies like Mars's moons, such as Phobos, which may experience less intense ejection pressures. This may necessitate a reevaluation of existing policies.
The team plans to further investigate whether repeated asteroid impacts lead to hardier bacterial populations or adaptation, and whether other organisms, including fungi, can survive these conditions.