Japan’s Martian Moons eXploration probe, known as MMX, is healthy and heading for Mars after the Japan Aerospace Exploration Agency (JAXA) confirmed on Wednesday, October 21 (Japan time) that its first critical sequence had finished. If the next five years go to plan, the mission will deliver at least 10 grams (0.35 ounces) of soil from the Martian moon Phobos to Earth in 2031, the first samples from a Martian moon ever brought to laboratories on Earth.
That third of an ounce sounds tiny, but researchers plan to measure the grains’ composition and minerals and set those chemical fingerprints beside Martian rocks and asteroid material, a comparison no orbiting instrument can make.
Liftoff came at 4:41:03 a.m. on Tuesday, October 20 at Tanegashima Space Center in Japan (3:41 p.m. Eastern on Monday, October 19). JAXA said the H3 rocket, on its 10th flight, flew as planned and released MMX 71 minutes and 13 seconds after liftoff.
Why a few grams could settle where Phobos came from
Two explanations compete. In one, Phobos and its smaller sibling Deimos are asteroids that Mars captured. In the other, they formed from debris thrown up when something large hit Mars. NASA’s MEGANE spectrometer will read the neutrons and gamma rays leaking from Phobos to map which elements sit on the surface.
The evidence so far pulls both ways. Viking images in the 1970s showed irregular, dark moons that resemble carbon-rich asteroids, which favors capture. But the mission team’s 2022 design paper in Earth, Planets and Space notes that capture was long considered dynamically difficult. The moons’ near-circular orbits above the Martian equator, meanwhile, fit the giant-impact picture. Lab analysis of real soil, possibly including rock blasted off Mars itself, is the test neither telescopes nor flybys can provide.
“As I watched the rocket H3 F10 soar into the sky, my thoughts went back to the very beginning of this project more than a decade ago,” JAXA project manager Yasuhiro Kawakatsu said in a statement released by the German Aerospace Center (DLR) after the launch.
How a 9,880-pound probe will sample a moon 14 miles wide
MMX weighed 9,880 pounds (4,480 kg) at launch, split between propulsion, exploration and return modules. After a cruise of about 10 months, it reaches Mars in August 2027. Phobos, about 14 miles (22 km) across, has too little gravity to hold a normal orbit, so the spacecraft will fly a quasi-satellite orbit, a looping path that keeps it close to the moon while both circle Mars.
Around the turn of 2028 into 2029 the probe drops a rover named Idefix, built by France’s CNES and Germany’s DLR, from 130 to 330 feet (40 to 100 meters) up. It will bounce, right itself and then drive for about 100 days at roughly 1 millimeter per second. Gravity there is under one thousandth of Earth’s, and the surface swings by more than 360°F (200°C) across a seven-hour day and night. The rover’s readings help pick the mothership’s landing site.
MMX carries two ways to grab soil. A coring sampler on a robotic arm reaches material deeper than about 0.8 inches (2 cm), and a pneumatic sampler near a landing foot uses a puff of pressurized gas to push loose grains into a container. NASA says the sampler mechanism came from Honeybee Robotics.
Three earlier Phobos missions failed, and this one has slipped by two years
The Phobos 1 and Phobos 2 probes of 1988 both failed, with Phobos 2 returning only limited data near the moon. Russia’s Phobos-Grunt, also designed to bring back soil, launched in November 2011, never left Earth orbit and fell into the Pacific in January 2012. Japan’s own Mars orbiter Nozomi lost contact on its way to Mars in the early 2000s.
JAXA’s small-body record is stronger: Hayabusa returned the first asteroid samples in 2010, and Hayabusa2 brought Ryugu material home in 2020. The 2022 design paper still listed a 2024 launch and 2029 return, so the timeline has moved two years.
Soil from one or two landing spots may not represent all of Phobos, and Deimos gets only flybys. NASA, which has invested about $87 million in the mission, is set to receive at least 15% of the planned sample. On a 10-gram return that works out to at least 1.5 grams (about 0.05 ounces), to be kept at Johnson Space Center in Houston.
What JAXA’s 2-hour, 17-minute launch broadcast shows
The English-language stream on JAXA’s own channel runs 2 hours, 16 minutes and 56 seconds. Separation came 71 minutes after liftoff, so a viewer who joins at the launch still has more than an hour of ascent to sit through before the moment that counts, when loud cheers broke out in mission control.
The broadcast records the H3 working in sequence, including a second upper-stage burn of about six minutes and 25 seconds that sent MMX toward Mars. Its limit is that it follows the rocket, not the spacecraft: confirmation that MMX was healthy came a day later, in a short written notice from JAXA. The spacecraft is now running functional checks of its onboard equipment ahead of the outbound cruise.
From here the calendar is long: arrival at Mars in August 2027, the Idefix drop around the turn of 2028 into 2029, sampling that NASA says will start no earlier than December 2028, departure for Earth in November 2030 after the Deimos flybys, and a capsule touchdown in Australia in 2031.
Further reading
- Wikipedia: Martian Moons eXploration
- NASA Science: MMX mission page
- Kuramoto et al. 2022, Earth, Planets and Space: MMX sample return mission to Phobos
Image: Andrea Luck, CC BY 2.0 via Wikimedia Commons
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