Japan's space agency, JAXA, will launch the first spacecraft designed to visit the Mars system and return to Earth. Liftoff from Tanegashima Space Center is set for 3:41 p.m. ET on October 19, which is 4:41 a.m. on October 20 in Japan.
The Martian Moons Exploration mission, or MMX, reaches Mars the following August and surveys both of its small moons, Phobos and Deimos. No earlier than December 2028, it will land on Phobos, stay about two and a half hours, collect soil, and turn for home. The return module sends down a capsule with at least 10 grams (roughly one-third of an ounce) in 2031. It lands in Australia, then the sample goes to Japan for cataloging.
Two samplers do the work. One, built by Honeybee Robotics, fires ultrapure nitrogen gas to blow soil into a container. The other pushes a tube into the top two inches of the surface. A small rover from the French and German space agencies rides along.
The prize is an answer to a real argument. In visible light, both moons resemble asteroids from the outer main belt, which points to capture by Mars' gravity. But their nearly circular orbits, lined up with Mars' equator, fit debris from a giant collision. MMX's Megane instrument, which reads gamma rays and neutrons, will also take the first measurements of the elements on Phobos.
The haul is modest. Hayabusa2 returned a bit more than 5 grams from the asteroid Ryugu, and OSIRIS-REx collected more than 120 grams from Bennu. MMX lands between them, but it is the first to collect from a moon other than Earth's.
NASA estimates its investment at about $87 million over 14 years. In return it supplied Megane and one sampler, and keeps at least 15 percent of the material.
The European Space Agency, another partner, said round trips like this could inform future missions that bring back samples from Mars itself. Phobos has weak gravity and no air, so it is far easier to land on than Mars, which makes it a lower-stakes rehearsal. The sample will not settle anything until 2031, five years after launch.