Salt-Loving Microbe Grew for 160 Days Under Simulated Mars Conditions

What grew, and how do we know?

Growth appeared in every low-pressure treatment containing nitrate or perchlorate. The researchers tracked it through optical density — essentially a measure of how cloudy a culture becomes as cells multiply.

The chemistry backed the headcount. Nitrate fell by about 15% to 29% and perchlorate by about 16% to 29% in the Mars-pressure cultures. Cell-free controls showed no such drops, which suggests the microbes were actually metabolizing the chemicals rather than the salts simply degrading on their own.

Two more findings stand out:

• Liquid loss stayed below 4% across all treatments over the full 160 days. Water normally boils off rapidly at such low pressure, which is exactly why long-duration experiments like this have been rare.
• Electron microscope images showed dense biofilm-like structures in the actively growing low-pressure cultures. The same structures did not appear in Earth-pressure controls or in low-pressure cultures that did not grow.

Raman spectroscopy — a technique that reads chemical fingerprints from scattered light — still detected signatures of carotenoid pigments. These pigments, which give many microbes their color, have been proposed as possible biosignatures, though the signals came back weaker than in oxygen-fed controls.

What does this change for the search for life?

Not much yet, and the paper is refreshingly honest about that. Growth at 24 millibars was significantly lower than in identical cultures kept at Earth pressure. The experiment also skipped several things Mars would not: no freeze-thaw cycles, no radiation, no full reproduction of Martian chemistry. The nutrient-rich growth medium, the authors concede, does not represent the sparse organics actually thought to exist on Mars.

There is a practical limitation too. The team measured cultures only at the start and end of the run, because cracking open the chamber would have let oxygen flood in and ruined the simulation. So we get two data points, not a curve.

The framing comes from the researchers' own logic. "The present-day Martian surface is generally considered inhospitable to life because of low atmospheric pressure, intense surface radiation, global desiccation, and oxidizing chemistry," they write. "However, shallow Martian subsurface regions where mineralogy has shown groundwater movement may include localized hypersaline environments capable of retaining liquid water and supporting microbial metabolism."

In other words: the surface is lethal, but salt pockets underground might hold liquid water, and this study shows at least one Earth microbe could make a living there.

"We are adding to the growing body of evidence suggesting that we should consider the possibility of life on Mars today," Dr. Robinson concluded.

Consider the possibility. That is the claim — no more. One organism, one chamber, 160 days, and a long list of things the simulation left out. Interesting evidence. Not proof of anything on Mars itself.