- Was Mars ever warm enough to support life? Scientists still don’t know exactly what the climate was like on Mars billions of years ago. But there are clues.
- Reduced forms of sulfur from active volcanoes could have kept the planet warm by creating a greenhouse effect. The findings are based on new atmospheric simulations and studies of Martian meteorites.
- These other forms of sulfur would have dominated the greenhouse process, rather than sulfur dioxide or carbon dioxide alone, as previously hypothesized.
Volcanic sulfur on Mars
Was Mars ever warm enough to support life? We know there was once abundant water on the surface. But scientists still don’t know exactly what the climate was like billions of years ago. Researchers at the University of Texas at Austin said on September 11, 2025, that volcanic activity likely helped keep the atmosphere warm enough for life to exist. They said sulfur gases released from volcanoes could have created the greenhouse effect needed to make the planet hospitable for life. The researchers ran over 40 computer simulations to study the possible atmosphere of early Mars.
Unlike previous models that suggested primarily sulfur dioxide or carbon dioxide, the new study shows that other reduced forms of sulfur might have been the dominant gases involved instead. Reduced sulfur refers to sulfur atoms in a negative oxidation state, forming compounds like hydrogen sulfide (H2S) and thiols (mercaptans).
The researchers published their peer-reviewed findings in Science Advances on September 3, 2025.
Volcanic emissions of reactive sulfur gases on early Mars may have contributed to a greenhouse effect, potentially creating conditions favorable for liquid water and microbial life. doi.org/g93fsc
— Science X / Phys.org (@sciencex.bsky.social) 2025-09-11T15:19:15-04:00
Simulating Mars’ early atmosphere
To try to determine how Mars’ early atmosphere could have been warm enough for life, the researchers ran over 40 computer simulations. The simulations used various temperatures and concentrations of gases and chemistry based on data from Martian meteorites. By doing so, the researchers could estimate how much carbon, nitrogen and sulfide gases were present billions of years ago.
Previously, scientists had considered sulfur dioxide or carbon dioxide to be the most likely gas to help create a greenhouse effect. The new results, however, suggested something a bit different: reduced and highly reactive forms of sulfur. This could include sodium sulfide (H2S), disulfur (S2) or sulfur hexafluoride (SF6). Sulfur hexafluoride, in particular, is an extremely potent greenhouse gas.
As lead author Lucia Bellino at the University of Texas at Austin explained, this could have resulted in a climate able to maintain liquid water and even support some forms of life:
The presence of reduced sulfur may have induced a hazy environment which led to the formation of greenhouse gases, such as SF6 [sulfur hexafluoride], that trap heat and liquid water. The degassed sulfur species and redox conditions are also found in hydrothermal systems on Earth that sustain diverse microbial life.
Sulfur kept changing forms
In addition, the study revealed that the sulfur might not have stayed the same. Instead, it kept changing forms. The meteorites contain reduced sulfur. But most of the sulfur that has been seen directly on the Martian surface is chemically bonded to oxygen. The difference suggests that this kind of sulfur cycling was common on early Mars. Bellino said:
This indicates that sulfur cycling – the transition of sulfur to different forms – may have been a dominant process occurring on early Mars.
Curiosity rover finds pure sulfur crystals
There’s another interesting twist to sulfur on Mars, too. In 2024, NASA’s Curiosity rover drove over a small rock, crushing it in the process. And the broken pieces revealed something unexpected. The rock was filled with crystals of elemental sulfur. Unlike other sulfur seen previously on the surface, this was pure sulfur, not bound to oxygen in sulfate. Co-author Chenguang Sun at the University of Texas at Austin said:
We were very excited to see the news from NASA and a large outcrop of elemental sulfur. One of the key takeaways from our research is that as S2 [disulfur] was emitted, it would precipitate as elemental sulfur. When we started working on this project, there were no such known observations.
Next, the team plans to use the same simulations to study the possible sources of water on early Mars, including volcanoes. In addition, they will investigate whether microbes could have used reduced sulfur as a food source.
Bottom line: Did early Mars support life? A new study shows how volcanic sulfur on Mars could have kept the planet warm and wet enough to be habitable billions of years ago.
Source: Volcanic emission of reduced sulfur species shaped the climate of early Mars
Via The University of Texas at Austin
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