A five-year round trip
Japan launched its Martian Moons eXploration spacecraft on Tuesday aboard an H3 rocket from Tanegashima Space Center. Liftoff came at 4:41 a.m. local time. The probe, built by JAXA, is 4,480 kilograms at launch and 2,100 kilograms dry.
MMX will spend about three years in the Martian system. It will map Phobos and Deimos, fly past Deimos and then descend to Phobos for one or two touch-and-go landings. It aims to collect at least 10 grams of surface material. A capsule carrying the sample is due back on Earth in 2031.
Two competing origin stories
Phobos and Deimos are small and dark. One idea holds that they are asteroids captured by Mars gravity. The other holds that they formed from debris thrown up when a large body struck Mars.
The two histories leave different chemical fingerprints. Captured asteroids should look like material from the outer asteroid belt, with particular water and organic signatures. Debris from Mars should carry the isotopic mix of the planet itself. "By bringing home samples from Phobos, we hope to explore how the martian moons were formed, how the Mars sphere evolved, and how the water and organic materials found on the terrestrial planets originated," project manager Kawakatsu Yasuhiro said.
What the samples could tell us
Phobos has almost no atmosphere, so its surface records impacts that Mars has erased. Material blasted off Mars may also sit in the regolith, giving scientists a sample of the planet without a Mars landing.
NASA contributed science instruments and ten participating scientists. The mission also tests technology for future human exploration, including landing and sampling on a low-gravity body. Japan has done this before: Hayabusa2 returned samples from the asteroid Ryugu in 2020. MMX is harder, because Phobos sits deep in Mars gravity and the round trip takes five years.
If the launch and cruise go to plan, the first Phobos samples will arrive in 2031.