Japan's MMX Mission to Land on Mars' Moon Phobos and Bring Samples Home

If you sneezed hard on Phobos, you would be in orbit around Mars. That's not a joke — escape velocity there is about eleven metres a second. Forty kilometres an hour.

You could jump off a moon.

You could jump off a moon. And on Tuesday morning, four forty-one a.m. Japan time, from an island off the southern tip of Kyushu, Japan is going to try to land a spacecraft on it anyway.

Tanegashima. October twentieth.

An H-three rocket, flight number ten, throwing a four-and-a-half tonne spacecraft at Mars. If it works, Japan becomes the first country to land on a moon of Mars, scoop up a piece of it, and fly it home.

A moon of Mars. Not Mars. Why does anyone care about a potato in orbit?

Here's the loop I want you to hold onto. A lot of serious people think the smartest way for humans to reach the SURFACE of Mars... is to stop at Phobos first. And nobody can tell you what Phobos even is.

What do you mean, what it is? It's a moon.

Two theories. Either it's an asteroid that wandered too close and got captured — or it's debris, rock blasted off Mars by a giant impact that clumped back together. Wildly different origin stories. David Lawrence, the physicist at Johns Hopkins who runs NASA's instrument on this mission, told The Planetary Society, quote, surprisingly, we have no idea.

NASA has an instrument on a Japanese mission?

It's called MEGANE — eyeglasses, in Japanese. Built by the Applied Physics Lab. Cosmic rays hit the moon, the moon glows back in gamma rays and neutrons, MEGANE reads the glow and works out which elements are there. But only up close. Lawrence says within about one body radius — roughly eleven kilometres.

How big is this thing we're hugging at eleven kilometres?

Twenty-seven kilometres on its longest axis. Lumpy, dark as charcoal, and so close to Mars it laps the planet in seven hours and thirty-nine minutes. From the Martian surface it rises in the WEST and sets in the east. Twice a day.

Okay, that's genuinely strange.

France and Germany are in, too — their space agencies built a little rover called Idefix. And this is the part that broke my brain. Idefix weighs twenty-five kilograms on Earth. On Phobos, according to the European Space Agency, it weighs about fifteen GRAMS.

Fifteen grams. That's a strawberry. So how do you land anything? Wouldn't you just bounce away?

Very carefully. The spacecraft descends for hours. It has to grab at least ten grams of regolith — a pneumatic sampler at the surface, plus a corer that drills about two centimetres down for material space hasn't cooked.

Ten grams. Years of flight for a teaspoon.

A teaspoon nobody has ever touched. Launch Tuesday, backup window to November seventh. Arrival in the Martian system around August twenty twenty-seven, Phobos orbit by September. Then roughly three years in looping quasi-satellite orbits, choosing a landing site. Samples home in twenty thirty-one, into the Australian desert.

That's five years of nothing going wrong.

Five years. And those would be the first samples ever returned from a moon other than ours — possibly containing bits of Mars itself, if the impact theory is right.

Wait. Japan might do Mars sample return before anyone does Mars sample return?

Not the same thing — Phobos dust isn't a chosen rock from a chosen crater. But while NASA's Mars sample return programme has been tangled in budget fights, and China aims Tianwen-three at the surface, Japan quietly built a round trip to the Mars system. Launching Tuesday.

So pay off the loop. Why Phobos for HUMANS?

Two decent arguments and one shaky one. First, communication. A crew sitting on Phobos could drive rovers, balloons, helicopters on the surface in real time — no twenty-minute delay to Earth and back. Phobos passes over key sites for hours.

You explore Mars without landing on it.

Second, radiation. NASA studies found a habitat on the Phobos surface could cut a crew's cumulative dose by up to thirty-four percent compared with just orbiting Mars — because the moon blocks half the sky.

And the shaky one?

Fuel depot. People love saying mine the water, make propellant. We don't know there's accessible water there — that's partly why we're going. And one NASA paper is blunt: on fuel alone, staging at Phobos buys you little over a regular Mars orbit.

So the gateway idea is a hypothesis, not a plan.

A hypothesis with engineering behind it — including a twenty twenty-five paper proposing a nuclear-thermal crewed Phobos mission in twenty thirty-five. Which is roughly when SpaceX and NASA talk about humans at Mars anyway.

Making MMX the rehearsal.

Everything a crew would face, MMX faces first. A window that only opens every twenty-six months. Capture into the Mars system. Descent onto a body with almost no gravity. Then the hardest part — leaving. Climbing back out of Mars' gravity well and hitting Earth precisely enough to drop a capsule in a desert.

Which is the exact manoeuvre you'd need to bring people home.

Exactly that. Except the samples don't complain, and nobody dies if the return engine doesn't light.

Bleak.

Honest. And there's a clock — Phobos is spiralling inward, about one point eight metres per century. In fifty million years, Mars tears it apart.

We've got time.

So, the standings. SpaceX has the biggest rocket and the refuelling problem. China has the clearest state timeline. NASA has the Moon. And Japan — French wheels, German engineering, American eyeglasses bolted on — has the only spacecraft in this window going to Mars and coming BACK.

And nobody's calling that a Mars mission.

They will in twenty thirty-one, when a capsule hits the Australian dust with ten grams inside. Anyone who ever walks on Mars has to come home... and Tuesday morning, somebody finally starts practising the hard half.