Japan's Martian Moons eXploration (MMX) spacecraft lifted off before dawn from the Tanegashima Space Centre, riding the country's flagship H3 rocket on the tenth flight of that launch vehicle. The rocket cleared Pad-2 of the Yoshinobu Launch Complex at 4:41 a.m. local time on Oct.

20, flying a nominal ascent over the Pacific before jettisoning its four solid boosters in pairs. Roughly 71 minutes after liftoff, and about a minute after a trans-Mars injection burn that pushed MMX to roughly 24,145 mph, the spacecraft separated from the upper stage on schedule.

JAXA flight controllers cheered and embraced when separation was confirmed an hour after launch, per The Guardian and space.com.

The Martian system has been visited many times — space.com notes NASA has landed nine spacecraft on Mars over the past half-century and China scored a touchdown in 2021 — but nobody has ever attempted a landing on Phobos or the smaller moon Deimos, and no mission has ever fetched samples from Mars or its moons.

Phobos itself is a lumpy, potato-shaped body about 14 miles (22.5 km) across, orbiting Mars three times a day roughly 6,000 km above the surface, where gravity is about 1/1,000th as strong as Earth's.

The $578 million, five-tonne spacecraft is a five-agency collaboration led by JAXA, with NASA, ESA, France and Germany as partners.

On arrival at Mars in August 2027, MMX will settle into a quasi-satellite orbit around Phobos and eject Idefix, a microwave-oven-sized French-German rover named after the terrier in the Asterix comics.

space.com and The Guardian report the four-wheeled rover will bounce for several minutes before settling, then spend 100 days surveying the surface to scout safe landing and sampling sites.

France 24 reports Idefix will crawl at just 1 millimetre per second, since it can no longer right itself once its solar panels deploy.

The main lander will then collect at least 10 grams of soil and rock in just two hours on the surface, with NASA's $87 million contribution earning it at least 15% of the sample for study at Johnson Space Center, according to space.com.

The samples target a decades-old mystery: how did Mars get two moons at all?

The competing explanations are the "giant impact" hypothesis, in which a collision with Mars ejected material that coalesced into Phobos and Deimos, and the "capture" hypothesis, which casts the moons as asteroids snared by Mars's gravity.

Their near-circular equatorial orbits point toward impact formation, while their potato shapes and telescopic composition hints suggest captured asteroids, space.com explains. Because Phobos likely holds traces of Martian material, the samples are effectively a two-for-one, per France 24.

JAXA says determining the answer could reveal how habitable environments arose on the terrestrial planets, and NASA says the findings will shape future Mars missions, including crewed expeditions.

MMX is scheduled to perform two touchdowns on Phobos, study Deimos during flybys, leave Mars orbit in November 2030 and drop its return capsule in the Australian desert in 2031.

That timeline puts Japan neck-and-neck with China, whose Tianwen-3 mission is slated to launch around 2028 and could return Mars surface samples as early as 2031, potentially before MMX.

NASA's own Perseverance rover has already collected more than 30 sample tubes, but The Guardian reports its return flight was halted by the Trump administration after a congressional vote in January.

"It is a once-in-a-lifetime chance. We are part of the first sample return mission from the Martian system," German Space Agency rover chief Markus Grebenstein said. Japan's two prior asteroid sample returns give it a rare edge going in.