Japan's MMX Mission Launches to Phobos, a Moon of Mars

There is a moon out there where, if you land too hard, you don't crash. You bounce. And then you keep going... up, and away, and you never come back.

You'd just... float off? That's a real failure mode?

That's the failure mode. Phobos is about twenty-two kilometres across. The gravity is so weak that Japan had to invent technology just to touch down, manoeuvre, grab a handful of dirt and not drift away doing it. And on Tuesday morning, they go.

Tuesday as in... this Tuesday.

Four forty-one and three seconds in the morning, Japan time. Tanegashima Space Center, an island off the southern tip of Kyushu. An H3 rocket, flight number ten. Evening of the nineteenth if you're in Europe.

Three SECONDS? They're timing it to the second?

Mars doesn't wait. There's a backup window, October twenty-first through November seventh, and after that you're waiting for the planets to line up again. The mission's called MMX, Martian Moons eXploration. JAXA runs it, with NASA, the European Space Agency, the French agency CNES and the German Aerospace Center on board.

Okay, but here's my dumb question. You fly all that way... and you skip Mars? Mars is RIGHT there.

Because nobody knows what Phobos actually is. And the two answers people argue about are wildly different. Option one: it's an asteroid that wandered too close and Mars grabbed it. Option two: something enormous slammed into Mars, blasted debris into orbit, and the debris clumped together into Phobos and Deimos.

So either it's a visitor, or it's a piece of Mars itself.

Right. And look what that does to the dating. Stickney, the big crater on Phobos, nine kilometres wide on a moon that's twenty-two across. In the giant-impact version, that crater is roughly four point two billion years old. In the captured-asteroid version, around two point six billion.

A billion and a half years of disagreement. About a rock we have photographs of.

Because the photographs show you the outside. The inside is what researchers literally call a known unknown. There's a paper this year by Haser and Andert in Monthly Notices of the Royal Astronomical Society. Haser says the captured-asteroid picture fits well, the shape is irregular, it looks like a rubble pile... and then he admits you cannot get the gravity field, the shape, the density and the orbit to all agree on one story.

So the honest answer is nobody knows.

The honest answer is nobody knows. Which is exactly why you fly. MMX carries a NASA instrument called MEGANE that reads gamma rays and neutrons to work out the composition. But the real prize is the sample. At least ten grams.

Ten grams. That's two teaspoons of dirt.

Two teaspoons. Worth five years and four space agencies, because on Earth you can put it under machines that are far too big and too power-hungry to ever fly. And then there's the bonus nobody will promise out loud.

Go on.

Phobos orbits so close to Mars that when meteors hit the planet, they fling Martian rock up onto its surface.

Wait. The Phobos sample might have actual Mars IN it.

Possibly. Mixed in. Delivered free, by the solar system. MMX even carries a dust monitor to hunt for particles knocked off Mars and Phobos while it's in orbit.

So Japan could bring home a piece of Mars before anyone brings home a piece of Mars.

Before NASA. Before China's Tianwen-three. That's the race underneath the race.

And none of this is the human part yet, is it.

No. Here's the human part. If Phobos is impact debris from Mars, it's probably bone dry, because that much heat drives the water off. If it's a captured asteroid, it could be water-rich. Water means hydrogen and oxygen. Which means propellant.

A petrol station. In orbit.

A truck stop before the planet. Somewhere to stop, refuel and wait, without hauling yourself out of a gravity well every single time. And we do not know whether there's fuel in it.

Okay. So when do we find out? Give me the schedule.

About a year of cruising. Mars orbit in August twenty twenty-seven, circling Phobos from September. Studying both moons from a distance through twenty twenty-eight. Early twenty twenty-nine, MMX drops a small rover called Idefix onto the surface.

A rover on a moon you can bounce off. Sure.

Then in twenty thirty, the spacecraft itself goes down. Grabs the sample, seals it into a return module. Flies past Deimos on the way out, takes one last look back at Mars... and reaches Earth in twenty thirty-one.

Twenty thirty-one. Same year China plans to land Mars rocks. No pressure.

None at all.

And if Tuesday goes wrong?

Then you wait for Mars to come back around. That's the brutal arithmetic of this entire series. The planets set the calendar, not us. ESA says it'll put out an image confirming a successful launch on October twentieth.

One picture. That's the whole verdict.

One picture. And then five years of silence before we learn the thing that actually matters... because every plan to put people at Mars assumes there's somewhere out there to stop and refuel. Phobos is the only candidate we've got. On Tuesday morning, Japan finally goes to ask it whether it's wet or dry.