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Today, Japan is launching the most ambitious round trip ever attempted in the solar system — not to Mars itself, but to one of its tiny, mysterious moons.
What is launching today
The Japan Aerospace Exploration Agency (JAXA) is targeting today, October 19 (3:41 p.m. EDT; 4:41 a.m. October 20 Japan time), to launch the Martian Moons eXploration mission — MMX — aboard its flagship H3 rocket from the Tanegashima Space Center. The goal: land on Phobos, the larger of Mars' two moons, scoop up at least 10 grams of its surface, and bring the sample back to Earth. If it works, it will be the first sample ever returned from a Martian moon — and, in the words of project manager Yasuhiro Kawakatsu, "the first round trip to the Martian system."
The spacecraft, developed at a cost of about 55.3 billion yen (roughly $350 million), is an international effort: NASA is contributing science instruments and researchers, with France's CNES, Germany's DLR and the European Space Agency also aboard. Before sampling, MMX will deploy a small French-German rover called Idefix — named after the dog in the Asterix comics — to scout the surface and make sure the landing site is safe.
Why Phobos is worth the trip
Phobos is a strange little world: just 22.2 kilometres across, with gravity so weak it could never pull itself into a sphere like our Moon. Its companion Deimos is even smaller at about 12.4 kilometres. And despite decades of Mars missions, the moons remain poorly explored — most of what we know comes from brief flybys.
Scientists genuinely don't know how Mars got its moons. One theory says Phobos and Deimos are captured asteroids, snagged by Martian gravity as they drifted past. Another says a giant impact blasted material off Mars itself, which then coalesced into the moons. A sample of Phobos' chemical makeup could settle the debate — and, as Kawakatsu notes, illuminate "how the water and organic materials found on the terrestrial planets originated." In other words, these 10 grams of rubble could help explain where Earth's water came from.
A long road home
Don't expect results soon. MMX will reach Mars about a year after launch, enter orbit around Phobos in September 2027, and spend roughly three years observing before the return module departs in November 2030 — with a flyby of Deimos on the way home. The sample capsule is scheduled to land in Australia's Woomera Prohibited Area in 2031.
The mission carries extra significance because someone else tried and failed. Russia's Phobos-Grunt spacecraft launched in 2011 but never made it past Earth orbit after its engines failed to fire toward Mars. JAXA is also explicit about a longer-term ambition: proving the technology for a round trip to the Martian system is, in the agency's words, "essential for crewed Mars exploration" — with Phobos potentially serving one day as a natural space station.
For skywatchers, this is a good season to look up for other reasons too — the Orionid meteor shower peaks this week, and our piece on the strange "treble clef" in deep space shows how much weirdness is still out there. But MMX is different: it's not just observing the solar system — it's bringing a piece of it home.
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