Experiment Shows Possibility of Martian Microbes Hitching a Ride to Earth

“Hearty bacteria in a lab survived pressures comparable to an asteroid strike on the red planet, suggesting a hypothetical scenario in which our planet was seeded with life.

 

No one really knows how life started on Earth, but one theory is that microbes hitched a ride on meteorites, and we’re the descendants of those tiny vagabonds. They may have even come from Mars.

 

“We have Martian meteorites” that made it to Earth after prehistoric asteroid strikes on the red planet, said K.T. Ramesh, an impacts expert at Johns Hopkins University. It’s easy to imagine one suffused with microbes plunging through Earth’s primeval skies.

 

This theory, known as lithopanspermia, remains unsubstantiated, not least because evidence of extinct alien life remains elusive on Mars. But Dr. Ramesh and his colleagues were curious if it was at least possible for microbes to hop between planets. Could bacteria survive if they were flung off a planet’s surface by an asteroid strike?

 

The team’s lab experiment offers compelling evidence that such a scenario is possible. Published Tuesday in The Proceedings of the National Academy of Sciences NEXUS, the team’s results have implications for how planets like ours might have been seeded with life.

 

No one is seriously claiming that we might have Martian ancestors. But this research shows that microbes cannot only brush off one of the most violent processes in the cosmos, but also take advantage of it to sail across the stars.

 

“We continuously redefine the limits of life,” said Madhan Tirumalai, a microbiologist at the University of Houston who was not involved with the new study. “This paper is another example.”

 

Scientists have long wondered if microbes can survive meteorite impacts. After all, plenty of organisms known as extremophiles survive high temperatures, extreme acidities and extraordinary salinities — sometimes all at once — on Earth. Others manage to persist in the face of intensive spaceflight clean-room protocols and make it all the way to space, clinging to the insides of spacecraft and even the outside of the International Space Station.

 

Microbes aren’t asteroid-proof — even relatively modest space rock strikes can unleash energies comparable to nuclear bombs, vaporizing micro-organisms at ground zero. But durable microbes on the edges of an impact site might be able to hitch a ride to space on jettisoned surface material.

 

For the study, the team at Johns Hopkins fired metal plates at microorganisms at tremendous speeds. The collisions generated extreme pressures associated with the sorts of asteroid impacts that commonly afflict Mars.

 

As for their unwilling microbial challenger, the team chose Deinococcus radiodurans. Found in the Atacama Desert in Chile, it’s the Incredible Hulk of the bacterial world: It can quickly self-repair, and it’s resistant to excessive dehydration, strong chemicals and powerful radiation — making it an excellent candidate for a microbe that could easily handle space travel.

 

The team sandwiched samples of D. radiodurans between two steel plates, then fired another metal plate at them at speeds of up to 300 miles per hour. The impacts generated pressures between one and three gigapascals, or between 10 and 30 times the pressure at the bottom of the Mariana Trench, the deepest oceanic chasm on Earth.

 

“We didn’t know what to expect,” said Lily Zhao, the doctoral student at the Johns Hopkins University who led the experiments. They didn’t have high hopes. “We would have been excited to see 1 percent survival, honestly.”

 

The bacteria proved to be tenacious. In the initial impacts, almost none of the bacteria perished. Even when the researchers ramped up the pressure, most of the bacteria appeared to be bulletproof.

 

At 1.4 gigapascals, an average of 95 percent of the microbes persisted. That dropped to 60 percent at 2.4 gigapascals, and just under 10 percent at 2.9 gigapascals.

 

The team couldn’t determine the impact pressure that would have exterminated the microbes — their experimental apparatus began to fall apart before the bacteria were wiped out. “The metals were failing and fracturing before the cells,” Ms. Zhao said.

 

Although its surface is now an irradiated wasteland, “Mars was very different billions of years ago,” Dr. Ramesh said — a realm decorated with lakes, rivers, perhaps even a giant ocean. Back then, asteroid strikes might have turned copious Martian microbes into astronauts.

 

Fresh off the smashing success of these experiments, Ms. Zhao hopes to put other kinds of bacteria, as well as additional microorganisms like fungi and archaea, at the end of her shooting gallery. She anticipates finding similar levels of adamantine resistance.

 

“Life is always hardier than we expect it to be,” Ms. Zhao said.” [1]

 

1. Experiment Shows Possibility of Martian Microbes Hitching a Ride to Earth. Andrews, Robin George.  New York Times (Online) New York Times Company. Mar 3, 2026.