MMX launch — Martian moon sample return

JAXA's Martian Moons eXploration — the first attempt to land on Phobos and return a sample to Earth (schedule may change).

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The story

MMX — Martian Moons eXploration — is JAXA's attempt to land on Phobos, collect surface material, and bring it home. If it works it will be the first sample ever returned from the Mars system, arriving before anything from the surface of Mars itself.

Phobos is small and strange. Roughly twenty kilometres across and shaped like a battered potato, it circles closer to its planet than any other moon in the solar system, completing a lap in less time than a Martian day. Its surface is dark and heavily cratered, and its orbit is slowly spiralling inward, so it is not a permanent feature of the Mars system either.

The spacecraft comes in three parts: a propulsion module to reach Mars, an exploration module carrying the instruments and performing the landing, and a return module that brings the capsule back. The plan is to spend years in Mars orbit, survey both Phobos and Deimos, descend to the surface at least once, secure a sample, and then wait for the window home. A small rover built by the French and German space agencies rides along and is released onto the surface ahead of the landing.

The launch date is the uncertain part. MMX was originally aimed at an earlier Mars window and slipped after problems with its launch vehicle. Because Earth and Mars line up for a transfer only about every twenty-six months, a missed window costs roughly two years rather than a few weeks. The date here is the current target, and the return date moves with it.

Why it matters

The central question is where Phobos came from. One account has it and Deimos as asteroids captured by Mars; the other has them assembled from debris thrown up when something large struck the planet. The two imply completely different histories, and decades of telescope and orbiter evidence have gone back and forth without settling it.

A sample settles it. Isotope ratios in returned grains act as a fingerprint of where material formed in the solar system, and laboratory instruments on Earth measure them at a precision no spacecraft instrument approaches. That is the whole justification for the complexity of sample return: a gram in a laboratory says more than a spacecraft in orbit.

There is a bonus as well. Phobos orbits close enough to Mars that material blasted off the planet by impacts should have rained onto it, so its regolith may hold Martian dust alongside Phobos's own rock. And whichever origin proves right, a body sitting that high in the Mars gravity well is an obvious staging point for later missions.

How to watch

There is nothing here for the naked eye. Phobos is a faint speck lost in the glare of Mars even through a large telescope. What you can watch is the launch, which JAXA streams live, normally with Japanese commentary and often an English feed alongside it. Japanese launches are frequently held for weather and pushed into following days, so check the time on the day itself.

The orbit view is where the mission becomes legible. Set the date to launch and the transfer geometry appears: Earth and Mars are not lined up on the day you leave but on the day you arrive, and the spacecraft flies the long curve between. Run the clock forward and watch Mars catch up with the probe.

After launch the interesting moments are spread across years: arrival and orbit insertion at Mars, the survey phase flying alongside Phobos to map it, the descent and sampling itself, and the departure burn that starts the ride home. Each is worth a reminder of its own, and the long quiet between them is normal for interplanetary flight.

See this for yourself — replay the moment in the orbit view

Background

Phobos carries a history of failure. The Soviet Phobos 1 and Phobos 2 probes were both lost in the late 1980s, one to a bad command and the other just before its close survey. Russia's Phobos-Grunt, aimed at sample return in 2011, never escaped Earth orbit. Nothing has landed there yet.

Japan's confidence comes from elsewhere. Hayabusa returned grains from the asteroid Itokawa after a nearly crippled flight home, and Hayabusa2 collected both surface and subsurface material at Ryugu and delivered it to the Australian desert on schedule. MMX inherits that capsule design and that operational experience, applied to a considerably harder target.

If a capsule comes back, the laboratory work will run for years, as it has for the asteroid samples. In the meantime China is preparing its own Mars sample return and NASA and ESA are reworking theirs, so the coming decade may bring several deliveries from the Mars system. The Phobos sample would be the first, the smallest, and possibly the most surprising.

FAQ

Why land on a moon instead of Mars itself?

Because it takes far less fuel. Phobos has a tiny fraction of Earth's surface gravity, so arriving and leaving needs very little thrust, and no atmospheric entry or landing system is required. There is also a chance that its regolith contains material blasted off Mars by impacts, which would deliver Martian rock as a bonus.

Exactly when does it launch?

Best not treated as fixed. MMX missed its original Mars window after problems with its launch vehicle, and the schedule has been adjusted since. Transfer windows to Mars open only about every twenty-six months, so missing one means waiting close to two years for the next. The date on this page is the current target.

Can I see Phobos through a telescope?

Not with the naked eye, and it is hard even with a telescope. Phobos orbits very close to a far brighter planet and is lost in its glare. Experienced observers sometimes attempt it near a close opposition using a large aperture and a technique that hides the planet's disk, but it is not a casual target.

When would the sample reach Earth?

It depends on when it launches. The plan has the spacecraft spending several years in the Mars system on survey and sampling before departing in a return window, so a delayed launch delays the delivery by the same amount. For now, early in the 2030s is the honest level of precision.

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Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.