What’s the first thing you think of when you hear the word “Mars”? The answer is probably rovers or dunes of pale red sand or maybe even apocryphal canals and science-fiction cities populated with little green men. But you probably don’t think of “moons,” even though Mars actually has two, named Phobos and Deimos. That’s because they’re both relatively small, unassuming space rocks rather than giant majestic orbs like Earth’s moon. Yet in some ways, they’re even more mysterious than our own natural satellite; we don’t know quite what they are, where they came from or how long they’ve been around. But we’re about to find out by grabbing a chunk of one.
On Monday afternoon EDT, the Japan Aerospace Exploration Agency (JAXA) will launch its Martian Moons Exploration mission (MMX). Over the next five years, MMX will travel to the Mars system, take samples from Phobos and return back to Earth.
The mission’s goal is to learn more about Phobos’s origins and those of the Mars system itself, said Lindsay Hays, NASA’s acting director of planetary science, in a press conference detailing the U.S. space agency’s contributions to MMX last week. NASA provided some of the scientific instruments, and several NASA scientists are actively involved in the mission.
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“The mission’s science and return samples will complement decades of Mars exploration and help inform future discoveries and perhaps, in the even further future, crewed missions,” Hays said. A proof-of-concept for retrieving Martian material is especially important to NASA because its own Mars Sample Return project is now stuck in limbo, with dozens of cached specimens awaiting pickup on the Red Planet’s surface.
“If you talk to the average person, they’re probably going to be more excited about a mission to a potentially habitable world or something like that and not a barren rock that is essentially a dented potato the size of Manhattan,” says Asa Stahl, an author and an astronomer at the nonprofit advocacy group the Planetary Society. “But there’s real science here.”
One of the biggest questions MMX could answer concerns the origins of Mars’s moons. It’s possible, scientists say, that Phobos and Deimos were two asteroids passing by that were each separately caught in Mars’s orbit. Or the moons could be pieces of debris that were created when Mars crashed into something else. By capturing samples of Phobos, researchers can better understand the composition of the moons and perhaps piece together the puzzle of their birth.
But beyond that, the samples will provide precious clues about the Mars system’s deep history—and possibly even about the history of life itself, says Wataru Fujiya, JAXA’s leader of the sample analysis team for MMX.
“Understanding the origin of Phobos would have implications far beyond Phobos itself,” he says. “Regardless of which hypothesis is correct, the origin of the moon involves interactions between a small body and Mars. Determining what kind of body interacted with Mars could therefore help us understand how the building blocks of life, such as water and organic matter, were delivered to terrestrial planets from external sources and how these planets evolved into worlds that could potentially support life.”
The mission is set to launch today at 3:41 P.M. EDT, to arrive at Mars in August 2027 and to study the moons for a few years before MMX lands on Phobos in 2030. MMX’s sample-return capsule, planned to carry at least 10 grams of Phobos, is expected to arrive back at Earth in 2031.
The mission carries 13 instruments, including two samplers, called the C-sampler and P-sampler. The C-sampler, a corer, will dig into the moon’s surface to extract material, while the P-sampler will blow high-pressure nitrogen gas at the surface to loosen and collect rocks and dust.
Bringing physical samples back to Earth is “one of the most scientifically bountiful things that you can do with a space mission,” Stahl says. “When we bring stuff back to Earth, then we can really dig down deep into it. We can throw all of our state-of-the-art equipment at it as much as we want. And most importantly, maybe, we can save some of those samples for equipment that we haven’t even invented yet.”
The mission involves an international collaboration among half a dozen space agencies, with Japan at the helm, and reflects JAXA’s years of investment in deep-space sampling work. The agency has also retrieved material from two asteroids, Itokawa and Ryugu.
“Japan has found kind of an interesting niche in its planetary and space science specialty—[with JAXA as] ‘the sample-return agency,’” says Casey Dreier, chief of space policy at the Planetary Society. “And they’ve gotten really good at it.”
If astronomers are really lucky, Stahl says, the retrieved bits of Phobos “could have a little bonus in them”: a piece of Mars itself. Scientists have calculated that when asteroids hit Mars, the planet’s gravitational field is meager enough that some of the ejected debris can readily reach Phobos. If the Phobos sample happens to include some of that debris, this would be the first physical samples of Mars returned to Earth. (Mars-sourced meteorites fall to our planet occasionally, but most are unrecovered, and none are pristine.)
“We might find kind of Mars rock that we’ve never had in hand before,” Stahl speculates. “I love to imagine some scientists, bent over an instrument in the laboratory, trying to pick out individual grains from Phobos and saying, ‘That one’s from Mars!’”