In recent years, scientists started scouring the skies for hints of life on worlds far outside our solar system. But some of the most tantalizing—and perplexing—clues to extraterrestrial existence might be a lot closer to home than we think.
Mercury—an atmosphere-less planet where temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius)—may have once hosted the chemical ingredients for life beneath its surface, according to a study published last week in the journal Scientific Reports.
Once in solid form, these crucial compounds may have been heated into gas by magma or exposure to the sun and escaped from the planet’s interior. Like a brittle, collapsing balloon, Mercury’s surface may have been destabilized by the gas’s rapid exit, generating craters, peaks and fractures that still exist on Mercury today, reports Shannon Hall for the New York Times.
Scientists previously theorized that Mercury’s so-called chaotic terrain was the result of a massive asteroid impact early on in its history—an event that fractured much of the planet’s landscape and peppered it with rocky debris.
But after analyzing data collected by NASA’s MESSENGER spacecraft, which orbited Mercury between 2011 and 2015, a team led by Alexis Rodriguez of the Planetary Science Institute began to explore alternative theories.
Though the asteroid’s untimely visit certainly reshaped the planet’s surface, the team’s data showed Mercury’s exterior continued to change for another couple billion years after the space rock hit, reports Passant Rabie for Inverse. In some spots, the terrain also appeared to have collapsed inward, toward the planet’s interior, as if the layer of crust below had simply disappeared—as if stilts holding the rocky surface in place had been kicked out from under it, study author Deborah Domingue tells the New York Times.
To reconcile the timeline of Mercury’s surface evolution with its caved-in appearance, the team devised a new hypothesis. One possible scenario, they argue in the paper, could involve the existence of volatile chemicals in the planet’s crust. Volatiles—a group that includes water—are substances that can easily transition from solids into liquids or gases when heated, potentially leaving gaping holes in their wake. In large enough amounts, these vaporization events can topple any terrains that might exist above them—perhaps reshaping planetary surfaces in the process.
Early on in Mercury’s history, heat from the planet’s interior likely drove this process, helped along by frequent exposure to the sun, reports Nicholas Gerbis for KJZZ. The volatiles’ origin, on the other hand, remains a mystery, though some of the chemicals may have been delivered by an asteroid collision—something researchers believed happened on Earth, according to a statement.
If volatile chemistry is indeed behind Mercury’s messy landscape, that could be exciting, as these compounds—especially water—are thought to play a big role in the inception of life. But hot gas alone doesn’t guarantee much. The team’s theory doesn’t guarantee what types of volatiles existed in the planet’s crust, if they ever did at all, or if they managed to come together in a way that seeded life.
But perhaps there’s reason for hope. Per KJZZ, water ice has been spotted at Mercury’s northern pole, raising the possibility that the vital compound once existed elsewhere on the planet as well. Though Mercury’s surface temperatures are searing, things are thought to be milder, and perhaps more permissive for life, deep down.
In an interview with the New York Times, Paul Hayne, a planetary scientist at the University of Colorado Boulder who was not involved in the study, remains cautious. “You could have transient pockets of high water activity,” below the planet’s surface, he says. “But I don’t think this is a case where we’d see massive pools of water and subsurface lakes and that sort of thing.”
Still, expanding this chapter of Mercury’s history could inform the search for life elsewhere in the galaxy. Volatiles like water might not be as rare as researchers once thought—and more traces of the precious stuff could still turn up in our own cosmic backyard.