Spacecraft Bound for Mars Aims to Settle Where Its Two Small Moons Came From

Japan’s space agency is preparing to launch a spacecraft that would land on Mars’s larger moon, Phobos, scoop up a sample and carry it back to Earth, a first round trip to the Martian system. The Martian Moons eXploration mission, known as MMX, is scheduled to lift off on an H3 rocket from the Tanegashima Space Center in southern Japan at 4:41 a.m. local time on Tuesday, which is Monday afternoon in the eastern United States, according to Agence France-Presse and NASA.

The spacecraft is expected to reach Mars in 2027. After surveying both moons, it will touch down on Phobos to collect at least 10 grams of surface material, AFP reported. NASA said sampling would come no earlier than 2028, after a detailed survey, and that the sample is due back on Earth in 2031. MMX will also observe the smaller moon, Deimos, without landing on it. A small rover named IDEFIX will go down first to study the surface and help the main spacecraft land safely.

Getting there and back is the hard part. Yasuhiro Kawakatsu, the mission’s project manager at the Japan Aerospace Exploration Agency, told AFP that going deep into what he called the gravity well of Mars is difficult.

The central scientific question is where the two moons came from. One idea holds that they are asteroids captured by Mars’s gravity long ago. Another holds that they formed from debris thrown into orbit when a large object slammed into Mars. NASA says the samples could settle the debate, and Tom Statler, the agency’s program scientist for MMX, noted that the moons may be the remains of such a giant impact. The answer could also shed light on how water and organic compounds reached the inner solar system, said Patrick Michel, a French astrophysicist working on the IDEFIX rover, according to AFP.

The mission is international. Japan leads it with France’s space agency, CNES, Germany’s aerospace center, DLR, the European Space Agency and NASA as partners. NASA contributed an instrument called MEGANE, built at the Johns Hopkins Applied Physics Laboratory, which will measure gamma rays and neutrons coming off Phobos to work out what its surface is made of. The agency also supplied a test sampler that uses bursts of pressurized nitrogen to gather material, and it will provide tracking through its Deep Space Network. In return, NASA will receive and curate about 15 percent of the returned sample at the Johnson Space Center in Houston.

Missions like this demand patience: the payoff is years away, with the sample not due back until 2031, and a landing on a small moon with weak gravity carries real risk. But the mission’s designers argue that analyzing material in laboratories on Earth can reveal far more than instruments flown to Mars. Nicky Fox, who leads NASA’s science directorate, said the samples would deliver paradigm-shifting science for generations to come.