What roles did volcanoes play on early Mars?
Lucia Bellino, PhD candidate at the University of Texas at Austin, takes a look back to find out.
Lucia Bellino is a doctoral student and National Science Foundation Graduate Research Fellow in her fourth year at the University of Texas at Austin in Austin, TX. Under the guidance of Dr. Chenguang Sun, Lucia’s research centers the cycling of hydrogen, carbon, and sulfur through high-temperature magmatic processes like magmatic degassing. She seeks to understand the connection between the interior and surface of planetary bodies through volcanism to investigate the potential habitability, climate, atmosphere, and evolution of Mars and Io.
Volcanic sulfur emissions may have played a key role in shaping the habitability of early Mars.
Observations of fluvial activity—landforms shaped by rivers and streams—suggest that Mars had a warm enough climate to sustain liquid water around 3 to 4 billion years ago. But the exact composition of the greenhouse gases that could have supported this climate remains a mystery.
Given the widespread presence of sulfur-bearing minerals on the Martian surface and in Martian meteorites, it’s likely that sulfur was a major atmospheric component. Volcanic activity could have transported sulfur from the planet’s interior to its surface.
Previous research suggested that early Martian volcanoes would have released sulfur primarily as sulfur dioxide (SO₂), which tends to cool atmospheres rather than warm them. Our research re-evaluates this assumption by accounting for a broader range of magmatic processes—especially how the crystallization of minerals from magma affects the composition of volcanic gases.
We find that instead of SO₂, sulfur would more likely have been released as S₂ (diatomic sulfur) and H₂S (hydrogen sulfide). On exoplanets, these gases are known to contribute to atmospheric haze by forming complex molecules. If such haze formed on early Mars, it could have significantly altered the planet’s climate.
Importantly, molecules derived from S₂ can react with fluorine gas (F₂) to form SF₆—sulfur hexafluoride—a greenhouse gas over 20,000 times more potent than CO₂.
Our findings suggest that volcanic emissions of S₂ and H₂S may have helped generate a hazy, greenhouse-rich atmosphere on early Mars.
