Humans have been dreaming about landing on Mars for more than a century, and NASA aims to finally achieve this vision in the coming decades. The question now is: Where should astronauts take the very first steps on Mars?
Arcadia Planitia, a flat region shaped by ancient lava flows, may fit the bill, according to a study published on Tuesday in Geophysical Research Letters. This area contains abundant deposits of shallow ice just below the Martian surface, which would enable astronauts to easily harvest their own water instead of lugging it over from Earth. The ice is so close to the surface that astronauts could get to it with hand tools, if they needed to.
“It’s just so complicated to bring anything from Earth,” said lead author Sylvain Piqueux, a planetary scientist at NASA’s Jet Propulsion Laboratory, in a call. “If you don’t have to bring your own water, you’re saving yourself a ton of money, space, and mass on your spacecraft and you can bring, instead, more interesting scientific instruments.”
NASA has long considered ice to be a requirement for a human landing site, but it also needs a site that is, well, not going to freeze astronauts to death. There’s plenty of ice at Mars’ poles, for instance, but those regions can be as cold as -150°C and are dark for months at a time, so a polar landing would be a risky venture.
For that reason, scientists think a site nearer to the equator would be the best fit because of the warmer temperatures and better balance of day and night. The northern hemisphere of the planet is also generally preferable because of its lowland plains, which give spacecraft more time and altitude to slam on the brakes before touchdown.
The abundance of shallow ice at those latitudes of the planet, however, was previously unclear. To hunt for these icy deposits, Piqueux and his team analyzed more than a decade of observations from two NASA spacecraft: Mars Reconnaissance Orbiter (MRO) and Mars Odyssey orbiter.
The scientists used heat-sensitive instruments on the spacecraft to detect shallow ice on Mars over the course of its seasons.
“Water ice has this very unique thermal behavior,” Piqueux explained. “It stores heat extremely efficiently. When we think of ice, we don’t necessarily think of it like that, but ice stores a lot of solar energy and heat.”
Counterintuitively, ice retains a lot of heat in the Martian spring and summer, warming the Martian surface, whereas the opposite pattern occurs in the fall and winter. “That’s the effect we were seeking that we found, and that we exploited with our models to figure out how deep the ice was,” Piqueux said.
Using this method, the team was able to show that Arcadia Planitia has ice buried only a few centimeters under its surface. A rake or a shovel would be enough to unearth—or rather, unMars—one of the most valuable resources that astronauts will need on an interplanetary adventure.
“From an engineering perspective, you don’t need to bring humongous equipment to extract it,” Piqueux said. “It’s so shallow that it should be very easy to access.”
“The novelty of this study is that now we can tell NASA: hey look, there’s these resources right here where it is reasonable to go,” he added. “Now this critical piece of the puzzle is there.”
These frozen resources would also be useful for scientific research, especially if it is “massive ice,” the type of stratified ice that forms in glaciers. Massive ice is like a layered record of a planet’s climate, and would contain all kinds of information about the past climactic patterns on Mars.
“It would give us access to another datapoint—a planet with an atmosphere, with a water cycle, but without an ocean,” Piqueux said. “What does that do to a climate? It would be a different way to look at the evolution of a climate and that is interesting in itself because it also helps us benchmark our own model for the Earth’s climate.”
If there are any aspiring Martian astronauts who want to get packed for Arcadia Planitia right after reading this, note that it’s worth cooling your jets for the moment. Piqueux and his colleagues plan to continue surveying potential landing sites for shallow ice in other regions, perhaps ones that could be even more conducive to humans than the Martian plains of Arcadia.
“Is there ice in regions closer to the equator that we’ve missed, or in places that could be potentially even more interesting?” Piqueux said. “I don’t know, but I’m predicting a lot more excitement to come.”