Scientists have spotted a relict glacier on Mars, near the equator—far from the parts of the planet where water ice is known to exist today. While this leftover glacial structure may not contain any water now, the fact that it exists where it does suggests that water ice had a more expansive footprint in the Red Planet more recently than previously believed.
A longstanding quandary about the Red Planet is when (and where) the planet’s water disappeared. Its surface is marked by evidence that water used to flow in rivers and lakes, but the landscape has been dry for seemingly billions of years. Scientists believe they’ve spotted subsurface lakes on Mars, but other researchers have suggested those are just big globs of clay. And those potential lakes are near the Martian poles, i.e., the colder parts of the arid and rocky world.
Last year, two more papers added fuel to the fire by arguing essentially opposite points: One found there was more evidence for subsurface lakes on Mars, and the other concluded the apparent signals of subsurface lakes were just reflections of layers of Mars’ interior.
Now, scientists are saying to forget about the Martian insides: there’s a glacial structure sitting smack on the surface, and not even toward its chilly poles but near the planet’s equator. The team’s research was presented last week at the annual Lunar and Planetary Science Conference.
The relict glacier sits in Mars’ Eastern Noctis Labyrinthus (labyrinth of the night), a stretch of switchback canyons at the planet’s midriff. The glacier itself is estimated to be about 3.73 miles long, 2.5 miles wide, and up to 1 mile high. NASA’s Mars Reconnaissance Orbiter captured images of the structure.
“What we’ve found is not ice, but a salt deposit with the detailed morphologic features of a glacier,” said study lead author Pascal Lee, a planetary scientist at the SETI Institute, in an institute release. “What we think happened here is that salt formed on top of a glacier while preserving the shape of the ice below, down to details like crevasse fields and moraine bands.”
There may still be water ice in the glacier—but there also may not. Mars has a very thin atmosphere and is very cold; temperatures generally fluctuate between 70 and -220 degrees Fahrenheit (20 to -140 Celsius). That means the water ice could have sublimated long ago.
The sulfate salts may have encrusted the glacier after volcanic activity on Mars in the not-so-distant past. At the boundary of the pyroclastic material—the ash, the pumice, what have you—and the glacier, a salt layer may have formed.
Erosion then rid the glacier of the pyroclastic layer, leaving the salty crust which reflects aspects of the glacier, whether or not its icy contents remain. Water ice is not stable right on the Martian surface, so if ice does remain in the glacier, it’s probably at a shallow depth, under the salts, Lee said.
The team suspects the feature is geologically young, belonging to the latest geological period on the planet. More observations need to be done to determine whether or not water ice is actually present there. If ice is there, it’s a boon to space agencies and individuals who hope to colonize Mars (we’re looking at you, Elon).
Finding ice close to the equator could allow humans to set up shop in a (relatively) more hospitable stretch of the planet. It would be warmer for humankind, though clearly still cold enough to keep water ice frozen.
But we’re getting ahead of ourselves. More research into similar structures may help scientists understand the conditions in which these relict glaciers form, and additional study of this one may reveal how much ice—if any—remains.