Japan launches spacecraft to bring home the first-ever samples from a moon of Mars

Japan's space agency launched a spacecraft early Tuesday on a mission to orbit, land on and collect the first samples ever taken from a moon of Mars, a project intended to settle a long-running dispute over how the Red Planet acquired its two small, misshapen satellites.

The Martian Moons eXploration spacecraft, known as MMX, lifted off atop an H3 rocket from the Tanegashima Space Center in southern Japan at 4:41 a.m. local time on Oct. 20 (3:41 p.m. Eastern time on Oct. 19). The launch came after a two-year delay caused by problems with Japan's new H3 rocket family, and after the Japan Aerospace Exploration Agency, or JAXA, waited for a planetary alignment that opens a practical launch window to Mars only once every 26 months.

The mission is led by JAXA but built with hardware and personnel from NASA, the European Space Agency, France's CNES and Germany's DLR. Officials with the agencies said the spacecraft's launch went as planned, with Carole Mundell, ESA's director of science, offering her congratulations "for this successful launch." Elliot Sefton-Nash, ESA's project scientist for the mission, said the team was "now even more motivated to prepare for arrival at Mars next summer."

A question that has lingered for 150 years

Mars has two small moons, Phobos and Deimos, discovered in 1877 and studied by every orbiter sent to the planet since. Neither looks like Earth's moon. Both are lumpy, cratered and only a few miles across, and both have long been difficult to classify. One leading explanation holds that they are asteroids that wandered too close to Mars and were captured by its gravity. A competing theory holds that they are the reassembled wreckage of a much larger object that slammed into Mars billions of years ago, scattering debris that settled into orbit.

Neither idea fits cleanly with what spacecraft have measured so far. Abigail Fraeman, a NASA scientist at the Jet Propulsion Laboratory, has said plainly that "none of our data fit either hypothesis correctly," and has described the two moons as "super weird, they're super small and they're super puzzling." Phobos, the larger and closer of the pair, is slowly spiraling toward Mars and is expected, within roughly 50 million years, to either crash into the planet or be torn apart into a ring; a crater called Stickney, blasted out by an ancient impact, covers roughly half its surface. Deimos, smaller and farther out, is slowly drifting the other way, outward from Mars, and is blanketed in dust.

MMX is designed to answer the origin question directly, by bringing physical material home. According to ESA's mission factsheet, the spacecraft will become the first ever to orbit Phobos, the first to collect a sample from its surface, and the first spacecraft of any kind to return to Earth from the Mars system. The plan calls for roughly three years of observation from orbit, followed by a landing in which a four-legged lander uses a coring drill that reaches about two centimeters into the surface, plus a gas-powered pneumatic sampler, to gather at least 10 grams of Phobos material for the trip home.

An instrument built to see beneath the dust

NASA's principal contribution to the mission is an instrument called MEGANE, short for Mars-moon Exploration with GAmma rays and NEutrons, built by the Johns Hopkins Applied Physics Laboratory with Lawrence Livermore National Laboratory. Rather than photographing Phobos, MEGANE will measure the neutrons and gamma rays that fly off its surface when it is struck by galactic cosmic rays, a process that reveals which chemical elements are present and in what quantities. According to APL's announcement of the instrument's launch, David Lawrence, MEGANE's principal investigator, said "Phobos has long guarded the secrets of its origins, and MEGANE will give us a powerful new way to uncover them."

Scientists are especially interested in what MEGANE finds in the way of volatile elements, such as hydrogen, sodium and chlorine, which behave differently depending on whether Phobos formed from icy, far-flung asteroid material or from debris blasted directly off Mars. NASA also contributed a technology demonstration sampling tool and tracking support through its Deep Space Network, and its scientists sit on the mission's international science team, as do researchers appointed by ESA. The spacecraft also carries a French-built infrared spectrometer and a small rover named Idefix, developed jointly by DLR and CNES, which is intended to scout the surface and help the mission's team pick a safe place to land. According to the mission's current schedule, laid out by NASA's mission overview and corroborating reports, Idefix is due to be dropped onto Phobos in early 2029 for a roughly 100-day scouting campaign ahead of the landing and sample collection.

"None of our data fit either hypothesis correctly."

What comes next

• Arrival in Mars orbit: expected around mid-2027, roughly a year after launch.
• Idefix rover deployed to scout Phobos: planned for early 2029.
• Landing and sample collection on Phobos: planned for no earlier than late 2028 into 2029.
• Departure from the Mars system, with a flyby of Deimos, followed by return of the sample capsule to Earth: targeted for 2031.

If the timeline holds, MMX's sample would reach Earth around the same time that China's Tianwen-3 mission is expected to return separate samples collected directly from the surface of Mars, giving planetary scientists two independent windows into the Mars system within a short span of each other. NASA scientist Daniel Glavin has said the early 2030s "could really be banner years of explanation for Mars," as material from multiple missions becomes available for laboratory study rather than remote sensing alone.

For now, MMX's engineers and scientists are focused on the months immediately ahead, checking out the spacecraft's systems during its yearlong cruise before it begins the delicate work of approaching and orbiting a body with barely any gravity of its own. Phobos is small enough that a spacecraft orbiting it moves at walking pace relative to the surface, a fact that makes both observation and landing there technically closer to maneuvering around an asteroid than to orbiting a planet or a larger moon. Mission planners from JAXA, NASA, ESA, CNES and DLR will spend the coming year refining those operations before Phobos itself, rather than computer models of it, becomes the subject of study.