3-4 billion years ago, Mars’ volcanoes spewed large amounts of sulfur-containing gases. And it was not sulfur oxide, as previously thought, but hydrogen sulfide and sulfur hexafluoride. These are much stronger greenhouse gases and could well have created a climate on the planet conducive to life.
Sulfur-containing gases and the early climate of Mars
Although the early climate of Mars remains an open question, new research suggests that its atmosphere may have been hospitable to life thanks to volcanic activity that released sulfur gases that contributed to the greenhouse effect.
Using data from the composition of Martian meteorites, researchers conducted more than 40 computer simulations with different temperatures, concentrations, and chemistry to estimate how much carbon, nitrogen, and sulfur gases could have been released on early Mars.
Instead of the high concentrations of sulfur dioxide (SO₂) predicted by previous climate models of Mars, their research shows that volcanic activity on Mars approximately 3-4 billion years ago could have led to high concentrations of several chemically “reduced” forms of sulfur, which are extremely reactive. These include hydrogen sulfide (H2S), disulfur (S2), and possibly sulfur hexafluoride (SF6), an extremely potent greenhouse gas.
According to lead author Lucia Bellino, a graduate student at the University of Texas at Jackson School of Geosciences, this could have led to a unique environment on Mars – one that could have been hospitable to certain forms of life. This means that the presence of “reduced sulfur” could have caused a foggy environment, leading to the formation of greenhouse gases such as SF6, which trap heat and liquid water. This could have created hydrothermal systems that support diverse microbial life.
The role of sulfur in the chemical processes of ancient Mars
Previous studies of Mars have examined how the release of gases on the surface, often as a result of volcanic eruptions, could have affected the planet’s atmosphere. This study, in turn, simulated how sulfur changed during geological processes, including how it separated from other minerals when incorporated into magma layers beneath the planet’s surface. This is important because it provides a more realistic picture of the chemical state of the gas before it was released onto the surface, where it could have shaped the early climate conditions on Mars.
The study also showed that sulfur may have frequently changed its form. While Martian meteorites have high concentrations of reduced sulfur, the Martian surface contains sulfur that is chemically bound to oxygen. “This suggests that sulfur cycling – the transition of sulfur into different forms – may have been a dominant process on early Mars,” Bellino said.
Last year, while the team was conducting its research, NASA made a discovery that seemed to confirm their findings. NASA’s Curiosity rover turned over and cracked a rock, revealing elemental sulfur. Although Mars is known for its abundance of sulfur minerals, this was the first time the mineral had been found in its pure form, unbound to oxygen. This was one of the confirmations of the research team’s hypotheses.
Further climate modeling
As the team continues its work, it will use its computer simulations to investigate other processes that would have been necessary to support life on Mars, including sources of water on early Mars and whether volcanic activity could have provided a large reservoir of water on the planet’s surface. They also seek to understand whether reduced forms of sulfur could have served as a food source for microbes in an early climate that resembled Earth’s hydrothermal systems.
Mars is far from the Sun, and today its temperature is typically cold, averaging -80°F. Bellino hopes that climate modeling experts will be able to use her team’s research to predict how warm the early Martian climate might have been, and if microbes were present, how long they could have survived in a warmer atmosphere.
Provided by: phys.org
