Salt-loving archaeon grew in a chamber built to mimic Martian subsurface brine

Haloferax volcanii, a salt-loving archaeon, grew in a chamber built to mimic a pocket of brine just under the Martian surface. The authors stress that the result does not mean life exists on Mars, according to a paper published online November 5, 2026 in Applied and Environmental Microbiology (doi:10.1128/aem.01749-26).

The mechanism is respiration without oxygen. Nitrate and perchlorate are both chemicals found on Mars, and the organisms can use them in place of oxygen to "breathe." Dr. Adam Robinson of the University of Florida and colleagues kept cultures in a vacuum chamber at 24 millibars, roughly 2% of Earth's sea-level pressure. The chamber was filled with carbon dioxide and scrubbed of oxygen, and the temperature was held at 21 degrees Celsius (about 70 degrees Fahrenheit). The cultures sat in an extremely salty liquid medium containing either nitrate or perchlorate. The researchers say this pressure could occur inside sealed fluid pockets in salt minerals at depths of about 20 cm (8 inches) below the Martian surface.

Growth appeared in every low-pressure treatment that contained nitrate or perchlorate, measured as increases in optical density, which tracks how cloudy a culture becomes. The researchers also measured drops in nitrate and perchlorate levels in the Mars-pressure cultures: nitrate fell by about 15% to 29% and perchlorate by about 16% to 29%. The drops did not occur in cell-free controls, which the researchers say suggests the microbes were metabolizing the chemicals.

Liquid loss stayed below 4% across all treatments over the 160 days, as the paper reports. That matters because water normally evaporates rapidly at such low pressures, which has made long-term experiments difficult.

Electron microscope images showed dense biofilm-like structures in the actively growing low-pressure cultures. They were not seen in Earth-pressure controls or in low-pressure cultures that did not grow. Raman spectroscopy also still detected chemical signatures of carotenoid pigments, which have been proposed as possible biosignatures, though the signals were weaker than in oxygen-fed controls.

Growth was significantly lower at 24 millibars than in identical cultures at Earth pressure, according to the team.

The authors write that 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 add that shallow subsurface regions where mineralogy has shown groundwater movement "may include localized hypersaline environments capable of retaining liquid water and supporting microbial metabolism." Robinson noted that the environment the experiment mimics has not been observed on Mars but is theorized to exist.

The design limits what the result can carry. The authors report that the experiment did not reproduce Mars's freeze-thaw cycles, radiation, or full chemistry. They also say the nutrient-rich growth medium is not representative of the organics thought to be available there. Cultures were measured only at the start and end of the run, because opening the chamber would have let oxygen in, so the course of growth in between is not recorded.

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