Mars has long been a planet of contradictions. Its dry river valleys whisper of flowing water, yet today it is locked in a deep freeze, with surface temperatures averaging -80 degrees Fahrenheit. Its thin atmosphere cannot hold much heat, and liquid water is unstable on its surface. And yet, for decades, scientists have found evidence that ancient Mars may have been warmer, wetter, and more hospitable to life than it is now.
But how? What force could have transformed a cold, distant world into one capable of sustaining water—and perhaps life itself?
A new study, published in Science Advances by researchers at The University of Texas at Austin, points toward an answer: Mars’ restless volcanoes may have filled the sky not only with ash and fire, but with unusual sulfur gases that trapped warmth and shaped a fragile climate window for life to exist.
Sulfur and the Breath of Volcanoes
Volcanoes are the lungs of planets. With each eruption, they breathe out gases locked deep in the crust and mantle, reshaping atmospheres and climates. On Earth, this has often meant injections of carbon dioxide, water vapor, and sulfur dioxide (SO₂). On Mars, scientists once thought SO₂ was the dominant volcanic gas too. Models suggested that SO₂ might have warmed the planet like a blanket, allowing streams and lakes to form billions of years ago.
But the new study tells a more complex story. By analyzing the chemistry of Martian meteorites and running more than 40 detailed computer simulations, the researchers found that Mars’ volcanoes may have released not just SO₂, but an array of reduced sulfur gases—molecules rich in sulfur but low in oxygen, such as hydrogen sulfide (H₂S), disulfur (S₂), and even sulfur hexafluoride (SF₆), one of the most powerful greenhouse gases known.
According to lead author Lucia Bellino, a doctoral student at the UT Jackson School of Geosciences, these gases may have made Mars’ atmosphere hazy and reactive, creating the conditions for warming and possibly for life.
“The presence of reduced sulfur may have induced a hazy environment which led to the formation of greenhouse gases, such as SF₆, that trap heat and liquid water,” Bellino explained. “The degassed sulfur species and redox conditions are also found in hydrothermal systems on Earth that sustain diverse microbial life.”
A Planet Shaped by Chemistry
What makes this study particularly groundbreaking is its approach. Instead of only modeling how gases behaved once they reached the surface, the team traced sulfur’s journey through Mars’ geology—how it separated from minerals deep within magma, how it traveled upward, and how it emerged during eruptions. This gave a far more realistic picture of the chemical state of Mars’ early atmosphere.
Their findings suggest sulfur didn’t remain in one form for long. Martian meteorites show abundant reduced sulfur, but Mars’ surface today is covered in oxidized sulfur—compounds bound to oxygen. This points to a vigorous sulfur cycle, a process of constant transformation that may have dominated early Mars.
That cycle could have done more than just alter the climate. On Earth, sulfur-rich environments like hydrothermal vents are teeming with microbial life, sustained by chemical energy in sulfur reactions. Early Mars may have mirrored these conditions, offering microbial pioneers the food and energy they needed to survive.
A Cosmic Coincidence: NASA’s Sulfur Discovery
As the team was deep into their research, NASA’s Curiosity rover made a discovery that seemed almost scripted for them. In 2022, Curiosity cracked open a rock and revealed pure elemental sulfur—the first time such a mineral had been found on Mars unbound to oxygen.
This find was thrilling for Bellino’s team. Their models had predicted that disulfur (S₂), once belched into the atmosphere, could settle back to the ground as elemental sulfur. Curiosity’s discovery provided a tangible piece of evidence that this sulfur cycle was real.
“We were very excited to see the news from NASA and a large outcrop of elemental sulfur,” said Chenguang Sun, Bellino’s advisor and co-author. “One of the key takeaways from our research is that as S₂ was emitted, it would precipitate as elemental sulfur. When we started working on this project, there were no such known observations.”
It was as though Mars itself had whispered back to confirm their theory.
The Prospect of Life on Early Mars
The implications of these findings reach beyond chemistry and climate—they touch on the possibility of life. If reduced sulfur gases warmed early Mars enough to sustain liquid water, and if those same gases provided energy sources similar to Earth’s hydrothermal systems, then Mars may have been more than habitable—it may have been lived in.
Life on Earth has shown an astonishing resilience, thriving in boiling vents, acidic pools, and frozen wastes. Microbes that “breathe” sulfur and feed on its chemical energy are well-known. On early Mars, with its sulfur-rich skies and possible hydrothermal activity, similar life forms might have found a niche.
A Planet of Questions
Still, many mysteries remain. How long could such a greenhouse effect have lasted? Was it stable enough to support lakes and rivers for millions of years, or was it fleeting, leaving behind only brief interludes of warmth? Did volcanic eruptions also provide water to the surface, adding to the planet’s reservoirs?
Bellino and her team are now turning their simulations toward these very questions, hoping to unravel how sulfur, water, and heat may have intertwined to make Mars briefly Earth-like.
And they are not alone. Across the world, scientists are piecing together Mars’ past from rover data, meteorites, orbital surveys, and laboratory experiments. Each clue brings us closer to understanding whether Mars was once a cradle of life or simply a tantalizing near miss.
The Bigger Picture: Why Mars Matters
The search for life on Mars is not just about the Red Planet. It is a mirror through which we examine our own origins. If life could emerge on Mars, even briefly, it strengthens the possibility that life is common in the universe. If Mars, with its sulfur skies and volcanic heart, could host microbes, then perhaps countless other worlds orbiting distant stars could do the same.
Mars also offers a cautionary tale. Today it is a barren desert, stripped of atmosphere and warmth. Studying how it transformed from potentially habitable to hostile may help us understand the fragility of climates—even our own here on Earth.
Conclusion: A Sulfur-Scented Memory
Billions of years ago, as lava welled up from the Martian interior and sulfur gases hissed into its sky, the planet may have glowed not only with volcanic fire but with the possibility of life. In those hazy, reactive atmospheres, heat may have lingered, water may have flowed, and microbial life may have stirred.
The new research from the University of Texas at Austin does not prove that Mars was once alive—but it makes that possibility harder to dismiss. Mars, it seems, may carry in its rocks and skies the memory of a warmer, more vibrant world, one shaped by the hidden alchemy of sulfur.
And so, the Red Planet remains more than a silent neighbor. It is a storyteller, reminding us that planets are dynamic, surprising, and sometimes—just sometimes—capable of harboring life.
More information: Lucia G. Bellino et al, Volcanic emission of reduced sulfur species shaped the climate of early Mars, Science Advances (2025). DOI: 10.1126/sciadv.adr9635
