life

In a major new report, scientists build rationale for sending astronauts to Mars

astronauts, life, Mars, NASA, Space / Shannon Garcia / December 9, 2025

The committee also looked at different types of campaigns to determine which would be most effective for completing the science objectives noted above. The campaign most likely to be successful, they found, was an initial human landing that lasts 30 days, followed by an uncrewed cargo delivery to facilitate a longer 300-day crewed mission on the surface of Mars. All of these missions would take place in a single exploration zone, about 100 km in diameter, that featured ancient lava flows and dust storms.

Science-driven exploration

Notably, the report also addresses the issue of planetary protection, a principle that aims to protect both celestial bodies (i.e., the surface of Mars) and visitors (i.e., astronauts) from biological contamination. This has been a thorny issue for human missions to Mars, as some scientists and environmentalists say humans should be barred from visiting a world that could contain extant life.

In recent years, NASA has been working with the International Committee on Space Research to design a plan in which human landings might occur in some areas of the planet, while other parts of Mars are left in “pristine” condition. The committee said this work should be prioritized to reach a resolution that will further the design of human missions to Mars.

“NASA should continue to collaborate on the evolution of planetary protection guidelines, with the goal of enabling human explorers to perform research in regions that could possibly support, or even harbor, life,” the report states.

If NASA is going to get serious about pressing policymakers and saying it is time to fund a human mission to Mars, the new report is important because it provides the justification for sending people—and not just robots—to the surface of Mars. It methodically goes through all the things that humans can and should do on Mars and lays out how NASA’s human spaceflight and science exploration programs can work together.

“The report says here are the top science priorities that can be accomplished by humans on the surface of Mars,” Elkins-Tanton said. “There are thousands of scientific measurements that could be taken, but we believe these are the highest priorities. We’ve been on Mars for 50 years. With humans there, we have a huge opportunity.”

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Life is thriving in the subsurface depths of Earth

Nitrospirota is an archaeal phylum that’s particularly common in the terrestrial subsurface. Some species of nitrospirota are capable of oxidizing ammonia, while others can reduce it to nitrite, which is used by phytoplankton and also defends against pathogens in the human stomach, mouth, and skin.

Proteobacteria is a bacterial phylum that’s especially abundant in the terrestrial and marine subsurface. Some proteobacteria live in deep ocean trenches, and oxidize carbon monoxide (which contributes to global warming and depletes ozone). Bacteria also common in the marine subsurface include Desulfobacteria and Methylomirabilota. Desulfobacteria reduce sulfates, and other sulfate-reducing bacterias have already shown they can be used to help clean up contaminated soil. Methylomirabilota help control methane levels in the atmosphere by oxidizing methane.

Something unexpected that caught Ruff’s attention was how total diversity went up with depth. This was surprising because less energy is available at deeper levels of the subsurface. For archaea, diversity went up with the increase in depth in terrestrial environments but not marine environments. The same happened with bacteria, except in marine instead of terrestrial environments.

Much of what lies far below our feet still eludes us. Ruff suggests that single-cell microbes in even deeper, yet unexplored levels of the subsurface may have adapted to the absence of energy by slowing down their metabolisms so drastically that it could take decades, even centuries, for them to divide just once.

If there really are microbes that manage to live longer than humans with this survival tactic, it is possible similar species might be hiding on planets such as Mars, where the surface has long been blasted by radiation.

“Understanding deep life on Earth could be a model for discovering if there was life on Mars, and if it has survived,” Ruff said in a press release.

Maybe future technology could retrieve samples several kilometers below the Martian surface. Until then, keep digging.

Science Advances, 2024. DOI: 10.1126/sciadv.adq0645