If the weather plays along, Japan will launch one of the most ambitious robotic missions of the decade on Tuesday morning local time. The Martian Moons eXploration spacecraft, better known as MMX, is scheduled to lift off on an H3 rocket from the Tanegashima Space Center at 04:41 Japan time on October 20, which is 21:41 Central European Summer Time on Monday, October 19. If the date slips, the space agency JAXA has reserved a backup window until November 7.
The goal is Phobos, the larger of Mars’s two small moons, and the plan is to bring a piece of it home. Nobody has ever orbited Phobos for long, landed on it or collected material from it. Scientists still argue about where the two moons came from: they may be asteroids that Mars captured, or the leftovers of debris thrown into orbit when something huge slammed into the planet. A sample of at least 10 grams should help settle the question.
The journey is long. MMX is expected to reach Mars in August 2027 and settle into an orbit around Phobos the following month. In early 2029 it will drop a small rover called Idefix, built by the French and German space agencies. The rover has a mass of about 25 kilograms, but Phobos has such weak gravity that it will weigh roughly as much as 15 grams would on Earth. In 2030 the main spacecraft is due to touch down, scoop up surface material and then head back, passing Deimos and Mars on the way.
The capsule with the sample is expected to land in Australia in 2031. With NASA and the European Space Agency also on board, MMX would be the first mission ever to travel to the Mars system and come back.
