New research suggests that temperatures on ancient Mars may have fluctuated between hot and cold periods through a relatively short period during its lifetime of billions of years. But these hot and cold spells may have been detrimental to life if it existed on the Red Planet.
Mars may be a dry and arid planet today, but scientists know that Earth’s neighbor was much wetter and much more like our planet in its ancient past.
These new findings from a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) suggest how Mars may have sustained its warmth and held on to its water billions of years ago.
“It’s been such a puzzle that there was liquid water on Mars, because Mars is further from the sun, and also, the sun was fainter early on,” team leader Danica Adams, NASA Sagan Postdoctoral Fellow, said in a statement. “It makes a really great case study for how planets can evolve over time.”
The team’s research was published new paper in Nature Geoscience.
The Martian hydrogen paradox
Scientists had previously theorized that Mars was able to hold on to its liquid water without it freezing despite its distance from the sun thanks to an excess of hydrogen in its atmosphere.
This element, the universe’s lightest, would bond with carbon atoms to form carbon dioxide in the Martian atmosphere. As we know all too well on Earth, carbon dioxide is a greenhouse gas that traps heat, causing a greenhouse effect. This could have kept Mars temperate enough to host liquid water on its surface.
The problem is that atmospheric hydrogen should’ve been short-lived around Mars.
This prompted the team to apply a similar process to Mars as is used on Earth to track pollutants, allowing them to model how the hydrogen content of the Martian atmosphere changed over time.
Adams and colleagues simulated how hydrogen would have mixed and reacted with other gases in Mars’s atmosphere and with chemicals on its surface. They found that Mars experienced episodic warm periods around 4 to 3 billion years ago.
These fluctuations occurred over the course of 40 million years, with each individual episode lasting at least 100,000 years.
These warm, wet periods would have been driven by Mars losing water from its atmosphere to the ground, which ironically refilled the hydrogen content of the atmosphere, thus sustaining the greenhouse effect.
The changes in Mars’ temperature were reflected by chemical changes, too, the team theorizes. Carbon dioxide would have been constantly reacting with sunlight to produce carbon monoxide. However, during warm periods the carbon monoxide would have changed back to carbon dioxide.
This recycling process would stall if Mars remained frigid for long enough, leading to a build-up of carbon monoxide and oxygen.
“We’ve identified time scales for all of these alternations,” Adams said. “And we’ve described all the pieces in the same photochemical model.”
What everyone really wants to know is if Mars could have ever supported life, albeit simple and microbial, in its ancient history. The existence of life may have been challenged during periods in which the temperatures dropped and oxygen levels climbed.
In the future, the team behind this study intends to compare their models to actual rock and soil collected from the Red Planet and returned to Earth by NASA’s proposed Mars Sample Return Mission.
“Early Mars is a lost world, but it can be reconstructed in great detail if we ask the right questions,” SEAS researcher and team member Robin Wordsworth said. “This study synthesizes atmospheric chemistry and climate for the first time to make some striking new predictions – which are testable once we bring Mars rocks back to Earth.”