Japan has launched a mission to bring samples back from Phobos, one of Mars's two small moons. The Martian Moons eXploration (MMX) spacecraft lifted off from the Tanegashima Space Centre aboard an H3 rocket, beginning a journey that is expected to deliver material from the moon to Earth by 2031.
The mission is led by the Japan Aerospace Exploration Agency (JAXA), with contributions from several international partners including the European Space Agency. The launch was described as a clean success by scientists involved in the project. «The launch was spectacular, and JAXA's H3 launcher performed fantastically to send MMX onward to Mars,» said Elliot Sefton-Nash, ESA project scientist for MMX. «The team are celebrating, and now even more motivated to prepare for arrival at Mars next summer to start investigating its moons Phobos and Deimos up close.»
Phobos is among the most puzzling bodies in the solar system. It is small, with a diameter of roughly 25 kilometers, and its irregular, cratered surface has led many scientists to suspect it is an asteroid captured by Mars's gravity. Yet its orbit is almost perfectly circular and lies nearly in the planet's equatorial plane — a path that would be highly unlikely for a randomly captured object. That has encouraged an alternative explanation: that Phobos formed alongside Mars, perhaps from debris thrown up by a collision between Mars and another celestial body.
Because the moon appears to have changed little over its history, its material could preserve a record of the early solar system and of Mars itself. Phobos is also slowly spiraling inward and is expected, in roughly 39 million years, either to crash into Mars or to break apart into a ring.
MMX is scheduled to enter Mars orbit next year. From there it will observe Deimos, the outer moon, which is thought to share Phobos's origins, before turning its attention to Phobos. The spacecraft carries 13 instruments, including cameras, a lidar device and spectrometers, which will survey the moon's surface before landing operations begin.
A small rover will be deployed to the surface first, followed by the main spacecraft. The mission will collect samples in two ways: one using pressurized gas to lift surface dust into a container, and the other a coring method that will extract material from about two centimeters below the surface. After departing Phobos, the craft will conduct a fly-by of Deimos in the late 2020s before heading home.
The sample capsule is expected to land in Australia before being transported to Japan, following the pattern set by JAXA's Hayabusa missions, which successfully returned material from an asteroid. The mission also follows an earlier attempt to explore Phobos: in 2011, Russia's Roscosmos launched the Phobos-Grunt spacecraft, but an engine failure after launch left it unable to set course for Mars.
If successful, MMX would provide the first direct samples from a Martian moon, giving researchers a new way to test competing ideas about how Phobos and Deimos came to orbit Mars and to study the early history of the Martian system.
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