At first glance, Mars' 500-mile-long Nanedi Valles looks like the Grand Canyon, with its steep-sided walls and plunging crevasses, two features that indicate a history of water.
However, the Mars we know today is one of freezing temperatures, arid conditions and, most importantly, a paper-thin atmosphere — all combined to create a hostile environment seemingly defiant of any life at all, let alone water.
See also: NASA's Mars-Bound MAVEN Seeks Answer to Climate Mystery
Scientists have floated the idea that meteorites assaulted the Red Planet billions of years ago, generating steam atmosphere to create the landscapes like the Nanedi Valles, a large valley that stretches 1.5 miles wide in some areas. However, it's more likely that an unusual greenhouse gas raised the planet's temperature to allow for flowing water.
A team of researchers at Penn State University used a one-dimensional climate model to show that molecular hydrogen, along with carbon dioxide and water, could have generated a greenhouse effect 3.8 billion years ago that drove up Mars' climate to above-freezing temperatures.
Previously, scientists used climate models that only included carbon dioxide and water. Ramirez and postdoctoral researcher Ravi Kopparapu built a model showing that gas levels from Mars' volcanic activity could have generated enough hydrogen and carbon dioxide to form a greenhouse and raise temperatures.
Ramirez then ran the model with new hydrogen absorption data and recreated an ancient Mars, where the sun was about 30% less bright than it is now.
"It's kind of surprising to think that Mars could have been warm and wet because, at the time, the sun was much dimmer," Ramirez said.
The team's model largely contributes to the understanding of the Red Planet's wet history, but Ramirez added that the only true way to prove its hypothesis was to test it in person.
"The best thing to do is send human geologists to the surface of Mars [...] to determine if early Mars was warm and wet or not," Ramirez said.
While the term "greenhouse gas effect" is often used in studies about Earth's climate, Ramirez said this particular discovery doesn't necessarily foreshadow our planet's future. Because Mars is a small planet, it doesn't operate as efficiently as Earth, and it's not good at holding onto its internal heat.
"Earth is much more massive and retained its heat much better, helping keep our magnetic field going," he said. "Thus, our atmosphere stayed relatively intact and has protected life on this blue pearl over the past 4 billion years."
However, Ramirez added that life on Earth will eventually cease to exist, but for very different reasons. With a gradually brightening sun, Earth's carbon dioxide levels will slowly drop and plants will no longer be able to photosynthesize. But this won't happen for another 1 billion years or so, according to Ramirez's calculations.
"Life on Earth is safe for quite a while longer," he said. "We won't have to think about claiming new real estate for quite some time yet."
The Nanedi Valles system on Mars. Image: ESA/DLR/FU Berlin (G. Neukum)
Image: NASA