# MMX: Japan heads to Phobos for a handful of dust that could rewrite Mars' history

> JAXA's MMX probe launches on an H3 on 20 October to bring more than 10 g of Phobos samples home by 2031. The $345m mission could show whether Mars's moons are debris from the planet itself.

- Published: 30 Sep 2026 (2026-09-30)
- Author: Stanislav Milchev, Editor
- Section: Missions
- Tags: MMX, JAXA, H3, Phobos, IDEFIX
- Canonical URL: https://www.spacecapex.com/en/news/japan-mmx-phobos-sample-return

On 20 October at 04:41 Japan time (22:41 Bulgarian time on the evening of 19 October), **H3 flight number 10,** is due to lift off from the **Tanegashima** Space Center with the MMX spacecraft on top, short for Martian Moons eXploration. The backup window stays open until 7 November, a sensible precaution for a mission that will be away from Earth for five years. It has already slipped once, from 2024, after the H3's maiden flight failed the year before, so nobody at JAXA is in a rush.

The target is Phobos, the larger of Mars's two small moons. It has a radius of about 11 km and looks like a crumpled, crater-pocked potato. The question the Japanese want to answer sounds academic but is fairly fundamental: are Phobos and Deimos asteroids from the outer Solar System captured by Mars's gravity, or debris from a giant impact on the planet? If it turns out to be the latter, samples from Phobos may contain material from Mars itself, blasted off billions of years ago. A surprisingly cheap ticket to Martian rock, if you ask me.

The engineering is more complex than it looks. The spacecraft weighs 4,480 kg at launch, more than half of it propellant, and is split into three modules: propulsion, exploration and return. It will arrive at Mars around a year after launch. Phobos is too light to orbit in the normal way, so MMX will use a so-called quasi-satellite orbit. It actually circles Mars, but in a way that traces loops around the moon. Orbital mechanics dreamt up by someone who doesn't want to commit.

![Phobos mission](https://omlclbaklhdpibyhxubz.supabase.co/storage/v1/object/public/media/articles/1790797194947-69mrmd.png "SpaceCAPEX")

Before the main spacecraft touches down, it will drop the **IDEFIX** rover, developed by France's **CNES**(**Centre National d'Études Spatiales)** and Germany's **DLR**(Deutsches Zentrum für Luft- und Raumfahrt), which will roam Phobos for at least 100 days. The idea is practical. The rover lands in a zone roughly 100 m across and surveys the terrain, then MMX heads for a much tighter 20 by 20 m site in the same area. With surface gravity of between 0.003 and 0.0068 m/s² (very roughly a thousand times weaker than Earth's), even the rover's wheels had to be redesigned. Otherwise every turn would have flung it upwards like a puff of dust.

The landing itself will be fully autonomous, because a signal takes around 20 minutes to travel between Earth and Mars. MMX will compare the terrain below with crater maps and, if something goes wrong, can pick a new spot on its own, abort the attempt and climb back up. The aim is to collect more than 10 g of material with two different samplers, one Japanese and one supplied by NASA, after which the capsule is due to land in Australia in Japan's 2031 fiscal year.

The price tag is around $345m, and this will be Japan's first probe to Mars in 28 years. By comparison, **NASA**'s Mars Sample Return mission has turned into a budgetary nightmare, while Japan wants to bring back material from the Martian system on a budget comparable to one large American satellite. If it works, **JAXA** will cement its reputation as the agency that pulls off the most complex sample-return missions with the least fuss. **Hayabusa and Hayabusa2** already proved that with asteroids. Now the stakes involve a planet.

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Source: SpaceCAPEX — https://www.spacecapex.com/en/news/japan-mmx-phobos-sample-return