Japan launches a round-trip mission to a Mars moon

JAXA plans to launch its MMX spacecraft from Tanegashima, Japan, on Oct. 19. Its target is Phobos, a Mars moon roughly the size of Manhattan. The plan is a true round trip. MMX will land on Phobos and scoop up about 10 grams of material. It will then launch back off and fly the sample home to Earth.

Phobos is small. But it has enough gravity that this isn't the easy 'touch and grab' used on asteroids like Bennu or Ryugu. MMX has to actually land on the surface. Then it has to launch itself back off — a maneuver no spacecraft has tried on a body this size. Scientists don't even agree on what Phobos is. One theory says it's an asteroid Mars captured long ago. Another says it's debris blasted off Mars by a giant ancient impact. A real sample, not just photos, should finally settle which story is true.

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Will the landing actually hold? Phobos's gravity is so weak that one wrong move could send the spacecraft bouncing back into space. JAXA won't know if the maneuver worked until it's already happening, millions of miles from any chance to fix it. Even a clean landing doesn't pay off right away. The sample won't reach Earth for years after liftoff.