Why the Japan MMX Phobos mission is so hard

Japan’s Martian Moons eXploration spacecraft, MMX, lifted off from Tanegashima Space Center on an H3 rocket at 3:41 pm EDT Monday, which was 4:41 am Tuesday in Japan, according to Ars Technica. The target is Phobos, the larger of Mars’s two moons. JAXA wants to land there, scoop up soil and bring it home.

Launching was the easy part. Phobos has a rough history with visitors, and the design of MMX reads like a list of answers to that history.

What did Japan launch, and what is it trying to do?

MMX is a five-year robotic mission with five space agencies involved: JAXA, NASA, ESA and the German and French agencies, per Wired and PBS NewsHour. It will study Mars and both moons from afar, then collect samples from Phobos.

Ars reports the spacecraft weighs nearly 9,900 pounds, about two-thirds of that propellant, and cost $578 million. The H3 flew in a new, more powerful configuration with four solid strap-on boosters, full-throttle main engines and a longer payload shroud. About 71 minutes after liftoff the craft separated from the rocket. It then checked in with controllers on the ground, opened its solar arrays and was reported to be in very stable condition. Ars calls it Japan’s heaviest and most ambitious interplanetary mission so far.

The science question driving it is how the moons formed. One camp says they’re captured asteroids, which fits their light-reflection patterns. The other says they’re debris from a giant impact on a young Mars, which fits their circular orbits lined up with the planet’s equator.

A poor track record at Phobos

Earlier attempts to reach Phobos failed. Wired says Russia sent three probes there starting in the 1980s and every one failed. That count comes from Wired alone, and the coverage doesn’t say what went wrong with each probe, so I won’t guess at causes.

What the record does tell you is that Phobos is an unforgiving place to work. Wired also notes that sampling it will differ from Hayabusa2’s visit to the asteroid Ryugu because Phobos has a different orbit and gravity. Techniques that worked at a small asteroid don’t simply transfer.

Kiyoshi Kuramoto, who leads MMX’s international science team, told Wired that bringing back samples from a Martian moon has never been done and won’t be easy.

How do two sampling methods and a scouting rover cut the risk?

MMX carries two different ways to gather soil, with a target of at least 10 grams, so a second approach is ready if the first fails, according to Wired. A rover is also planned to land ahead of the main spacecraft and explore the terrain.

That ordering matters. The landing site can’t be picked until MMX makes close-up observations of Phobos, so the mission is built to look first and commit later. The sequence, as Wired lays it out, is observation, then the rover landing, then the main spacecraft landing and collection.

Redundancy is the oldest trick in spaceflight, but it fits the problem here. When nobody has landed on the target before, you can’t be sure which approach the surface will tolerate. Having two ways to get soil is a hedge against ignorance, and the rover is a hedge against a bad landing spot. What the rover will do on the surface, and for how long, isn’t yet reported. Details of the two sampling methods themselves also weren’t in the coverage.

What does Hayabusa experience bring?

Quite a lot of human experience. JAXA’s Hayabusa returned material from the asteroid Itokawa in 2010, and Hayabusa2 returned samples from the asteroid Ryugu in 2020. Wired and Ars both report that many Hayabusa2 team members helped design MMX.

That’s the part of the risk story I find most reassuring. Hardware gets rebuilt, but the people who have actually brought rock home from deep space carry judgment that doesn’t live in a spec sheet. It doesn’t guarantee a result, because Phobos isn’t Ryugu, and the gravity and orbit differences are exactly why the sampling plan can’t be copied wholesale. Still, a team that has done sample return twice is a better bet than one doing it for the first time.

What is MMX hoping to find?

The payoff is large if it works. Wired reports that researchers suspect Phobos’s surface soil contains Martian material, which could show how Mars evolved. Wired also says the samples would be the first returned from a moon other than Earth’s; that claim comes from Wired only.

The MEGANE instrument will measure Phobos’s elemental makeup. According to Wired, more volatiles such as hydrogen or potassium would favor the captured-asteroid idea, and fewer would favor the impact idea. David Lawrence, who leads the MEGANE team at Johns Hopkins University, told Wired: We know nothing about Phobos’ elemental composition.

Why an enthusiast should care

For anyone who follows spaceflight, this is a rare mission where the risk is the story. You can watch how a team designs around a target with a bad record: scout first, sample two ways, lean on experienced hands. The result will tell us whether that approach works on a body nobody has touched.

It’s also a reminder that rockets are only the opening act. Launch reliability has its own drama elsewhere, as with a grounded New Glenn in the US. MMX cleared that first hurdle and now faces about 10 months of cruising, per Ars. Wired says almost a year, so treat the arrival date as approximate until JAXA publishes one.

If this makes you want to look at Mars yourself, a beginner-friendly scope such as the Celestron NexStar 8SE is one way to start. It won’t show you MMX, but it’s a decent way to get familiar with the sky the mission is headed toward.

What nobody can say yet

Most of the hard questions are still open, because the hard parts happen after arrival. Where MMX will land on Phobos isn’t decided, since close-up observations come first. Whether it can succeed where earlier missions failed is the central question, and it won’t be answered for years.

Other gaps: the exact launch date and Mars arrival date aren’t stated in the coverage, and each partner agency’s precise contribution isn’t spelled out beyond MEGANE and a few roles. Wired was written before launch and speaks in the future tense, so the landing, the sampling and the 2031 return are all targets, not achievements.

JAXA president Hiroshi Yamakawa marked the launch by saying a five-year effort had just started, per Ars. Japan’s science minister, Yoshihiro Seki, and project manager Yasuhiro Kawakatsu also commented, according to the same report. For now, the one clear result is a healthy spacecraft heading for Mars.

Frequently asked questions

What is the MMX mission?

MMX, or Martian Moons eXploration, is a JAXA spacecraft launched toward Mars to study its moons and collect at least 10 grams of soil from Phobos. The goal is to return the samples to Earth by 2031.

How long does MMX take to reach Mars?

Ars Technica says about 10 months, while Wired says almost a year. An official arrival date hasn't been reported.

Why did earlier Phobos missions fail?

Wired reports that Russia sent three probes starting in the 1980s and all failed. The coverage doesn't explain the causes.

How is MMX trying to avoid those failures?

It plans two different sampling methods as a backup, lands a rover ahead of the main craft to scout terrain, and draws on Hayabusa2 team members who helped design it.

Sources

This article was compiled from reporting by the following outlets. Links go to the original reports.

1. PBS NewsHour: Japan launches spacecraft to Mars' moon in mission to bring back soil samples
2. Wired: Japan’s MMX Mission Wants to Bring Martian Moon Samples Back to Earth
3. Ars Technica: Japan launches mission to bring home a piece of the Martian moon Phobos
4. Ars Technica: Japan launches mission to bring home a piece of the Martian moon Phobos