TANEGASHIMA, Oct. 15 -- Early on October 20, Japan time, an H3 rocket is due to lift off from the Tanegashima Space Center carrying a spacecraft with an unusual errand: reach a moon of Mars, scoop up at least 10 grams of it and bring it home. The European Space Agency confirmed the launch time, 04:41 JST, in a release this week.

The Martian Moons eXploration mission, known as MMX, is led by JAXA with NASA, France's CNES, Germany's DLR and ESA. It will be the first mission to collect a sample from Phobos and the first to return to Earth after visiting the Mars system.

The science question is older than the spacecraft. Nobody knows where Phobos and Deimos came from. They may be asteroids captured into Mars orbit, or debris thrown up when ...