Scientists Grew Microbes in Mars-Like Conditions for 160 Days. They Didn’t Just Survive, They Thrived

An experiment shows that salt-loving microorganisms can reproduce under some of the harsh conditions thought possible beneath Mars' surface, raising new questions about whether life could exist there today.

Mars is cold, dry, and almost airless. But in a laboratory on Earth, scientists recreated some of its harshest conditions and watched microbes do something remarkable: multiply.

For 160 days, the organisms grew without oxygen, under extremely low pressure, and in water seven times saltier than seawater. The experiment suggests that life might be capable of more than merely surviving beneath the Martian surface.

A protective coating against a hostile world

The researchers studied Haloferax volcanii, a salt-loving microorganism belonging to a group called archaea. Archaea look like bacteria but belong to a separate branch of life. Many of them thrive where other organisms struggle, from scalding hot springs to extremely salty lakes.

That made H. volcanii a promising candidate. Mars contains salts that could potentially keep water liquid underground, even below its normal freezing point.

Previous experiments had shown that Earth microorganisms could survive certain Martian stresses, including low atmospheric pressure and highly salty water. Some had even combined several of these conditions, but typically for just hours or days.

But surviving an environment is fundamentally different from thriving in it.

“Far fewer have been able to combine these conditions together and show that microorganisms can actively grow,” said Adam Robinson, a University of Florida researcher who led the study.

The team put H. volcanii to the test. They placed the microbes in a low-pressure, carbon dioxide-rich environment without oxygen. The organisms lived in brine seven times saltier than seawater, with either nitrate or perchlorate available to help them generate energy without oxygen.

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Perchlorates are particularly interesting. These chlorine-containing compounds have been detected on Mars and can lower water’s freezing point, potentially allowing salty liquids to persist under otherwise freezing conditions.

For 160 days, the microbes kept growing. Slowly, certainly, but they were multiplying. When researchers withheld both nitrate and perchlorate, the organisms remained alive but showed no measurable growth.

With the right chemistry, the microbes weren’t simply hanging on. They were actively sustaining themselves and reproducing.

A protective coating against a hostile world

The researchers spotted another curious adaptation. Under low pressure, the microbes clustered into dense, biofilm-like communities. Biofilms are groups of microorganisms embedded in a protective matrix, commonly found on river rocks, teeth, and countless other surfaces.

These microbial clusters may have helped keep the salty water from evaporating. Over the entire 160-day experiment, the cultures lost less than 4% of their liquid, despite the low atmospheric pressure. The concentrated salt solution itself also slowed evaporation, so it’s unclear how much extra protection the biofilms provided.

On Mars, where liquid water is scarce and unstable, even a little protection could matter.

But the experiment wasn’t a perfect recreation of the Martian underground. The cultures were maintained at approximately 70 degrees Fahrenheit (21 degrees Celsius), considerably warmer than most of the Martian subsurface. Scientists also supplied nutrients, something that might be difficult for organisms to obtain naturally.

And there’s a more fundamental problem: nobody has actually found the underground pockets of salty water that the researchers were attempting to simulate. We suspect they could exist, but this isn’t yet proven.

“The environment that we’re mimicking in this experiment has not been observed on Mars, but is theorized to exist,” Robinson said.

Could life still exist beneath Mars?

For decades, scientists have focused much of their search for Martian life on the distant past. Ancient riverbeds, lake deposits and other geological features suggest that billions of years ago, Mars was warmer and wetter, potentially offering suitable conditions for microorganisms.

But what if some of that ancient life never disappeared? What if it simply retreated underground as the planet became colder and drier?

Scott Perl, a researcher at the Natural History Museum of Los Angeles County and the Blue Marble Space Institute of Science who co-led the study, argues that scientists may need to rethink what makes an environment habitable.

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“They’ve evolved within the Martian environment that we consider hostile. So what is hostile to us isn’t necessarily going to be hostile to those microbes,” Perl said.

He’s speaking hypothetically, of course. No Martian organisms have ever been discovered. But if life did emerge there billions of years ago, it would have had an extraordinarily long time to adapt to its changing home.

The experiment also has practical implications. Understanding how microbes behave in Mars-like environments could help future missions distinguish traces of ancient life from signs of organisms that are still metabolically active. It could also help scientists assess the risk of contaminating Mars with microbes carried from Earth.

This doesn’t mean Mars harbors life today. The experiment recreated a habitat that scientists have yet to find on the Red Planet.

But it raises a tantalizing question. If microbes can grow under conditions this extreme on Earth, what might be happening in the dark beneath Mars?