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MMX, Japan's Phobos sample-return mission, launches Oct. 20

JAXA's MMX is set to launch at 4:41:03 a.m. Japan time on October 20, 2026 (19:41:03 UTC on October 19) for Phobos, with a sample due back in 2031.

By the WatchSat editors · · 5 min read

Phobos, the larger of Mars's two moons, in colour from the HiRISE camera on NASA's Mars Reconnaissance Orbiter, about 6,800 kilometres away on March 23, 2008, with the large crater Stickney at lower right
Image: NASA/JPL-Caltech/University of Arizona · Public domain

Japan's Martian Moons eXploration spacecraft, MMX, is set to lift off from the Tanegashima Space Center at 4:41:03 a.m. Japan time on Tuesday, October 20, 2026. In UTC that's 19:41:03 on Monday, October 19, or 3:41 p.m. Eastern. The Japan Aerospace Exploration Agency (JAXA) plans to land it on Phobos, the larger of Mars's two moons, collect a sample of 10 grams or more and bring it home in 2031.

The European Space Agency (ESA) says MMX will be the first mission to land on Phobos and the first to return a sample from the Mars system.

When is the MMX launch?

JAXA announced on August 20 that MMX will launch at 4:41:03 a.m. Japan time on October 20, 2026. It holds October 21 through November 7 as a backup period, with a new launch time each day.

Sources give two dates because of time zones. JAXA, NASA and CNES say October 20, the date in Japan. DLR and Space.com say October 19, the date in UTC, Europe and the United States. We checked JAXA's time against Launch Library 2, the feed behind our launches page, which lists 2026-10-19T19:41:03Z. Japan runs nine hours ahead of UTC, so the two agree to the second.

The rocket is H3 flight No. 10, an H3-24L in JAXA's naming: two main engines, four solid rocket boosters and the long payload fairing. JAXA calls it the most powerful H3 version and says the 24 configuration has flown once before, while this is the first launch with the long fairing. Launch Library shortens the name to H3-24.

H3 flight No. 8 failed on December 22, 2025, leaving the Michibiki 5 navigation satellite short of its planned orbit. JAXA's July 23 report traced the failure to a payload adapter whose bonded joints had delaminated in manufacturing and gave way at fairing separation. It calls for bolted joints on standard missions and for inspecting every flight fairing. Flights No. 6 and No. 9 have launched successfully since, on June 12 and August 11.

What will MMX do at Phobos?

MMX has three modules: a propulsion module, a lander and a return module carrying the sample capsule. Once at Mars it moves into what JAXA calls a quasi-satellite orbit, which follows Phobos around the planet and, seen from the moon, looks like an orbit around it.

Phobos measures 27 by 22 by 18 kilometres, NASA says, and circles Mars three times a day. It's closing in on the planet by 1.8 metres every hundred years, and NASA expects it to hit Mars or break up into a ring in about 50 million years.

A 25-kilogram rover called Idefix, built by the French and German space agencies, CNES and DLR, will land first, JAXA says, to measure the surface and help the main spacecraft touch down safely. ESA says it will weigh the equivalent of about 15 grams on Phobos, and DLR expects the landing in early 2029. The main spacecraft will then land, twice by JAXA's plan, and collect material with a corer and a pneumatic sampler.

NASA supplied MEGANE, a gamma-ray and neutron spectrometer that will measure the elemental makeup of Phobos's surface. NASA says scientists suspect the moons are either remnants of an ancient collision between Mars and a large impactor or captured asteroids, and that MEGANE's readings should help show which.

Deimos, the smaller moon, gets late-mission flybys rather than a landing, JAXA says.

Two colour-enhanced HiRISE views of Deimos, the smaller of Mars's two moons, taken 5 hours and 35 minutes apart on February 21, 2009, with the Sun to the upper left in the left image and to the right in the second
Deimos, about 12 kilometres across, in two enhanced-colour HiRISE images from NASA's Mars Reconnaissance Orbiter taken 5 hours and 35 minutes apart on February 21, 2009. Image: NASA/JPL-Caltech/University of Arizona · Public domain

Sources differ on a few other numbers too.

What to watch, and where to follow it on WatchSat

These are JAXA's plans, and launch dates slip.

Our launches page lists the launch as "H3-24 | Martian Moon eXplorer (MMX)", with a live countdown and the time in your time zone.

The Phobos card on our solar system page opens with the same HiRISE colour image as the top of this post. It lists Phobos at 9,378 kilometres from Mars. NASA's Mars fact sheet gives the same figure, measured to the planet's centre. Take away Mars's 3,396-kilometre equatorial radius and Phobos sits about 5,980 kilometres above the surface.

Our deep space page shows live distances and signal times for craft such as Voyager 1. MMX isn't one of them, but JAXA says its farthest point from Earth will be 2.5 astronomical units, a round trip of about 40 minutes for a radio signal.

Sources

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