Five of the world's space agencies joined forces for the five-year mission that will attempt to land a robotic prospector plus a rover on Phobos, the larger and closer of Mars' two pint-sized moons.
The Japan Aerospace Exploration Agency, which is leading the bold sampling effort, launched the spacecraft before dawn on Tuesday from the country's main spaceport on Tanegashima Island.
Officials declared success an hour later when the spacecraft separated as planned from the rocket's upper stage. Flight controllers burst into applause and jumped to their feet, shaking hands and embracing.
While NASA has successfully landed nine spacecraft on Mars over the past 50 years and China scored a 2021 touchdown, no one has ever ventured onto Phobos or its sidekick Deimos. And no one has managed to fetch samples from Mars, let alone its moons.
If successful, bits of dust, soil and rocks from Phobos will arrive on Earth in 2031.
"There's a lot of adrenaline and a lot of excitement and a lot of wow," said NASA astrophysicist Tom Statler, who's involved with the project.
Japan has an edge going in, with two asteroid sample returns already under its cosmic belt.
Phobos is a lumpy, potato-shaped rock just 22km across. Examining pieces of it can explain how Mars' moons - and possibly moons elsewhere - came to be.
Dubbed MMX for Martian Moons Exploration, the $US578 million ($A828 million) mission features a hefty five tonne spacecraft that should reach Mars by next northern summer.
It will sync up with Phobos' tight orbit around the red planet, before ejecting the French-German rover that's named Idefix after the white terrier in the Asterix comics.
No bigger than a microwave oven, Idefix will plop onto Phobos by itself, bouncing for several minutes before coming to a halt in the moon's extraordinarily low gravity.
The four-wheeled rover is designed to right itself if it lands upside down.
All bets are off, though, if it sinks into soft soil or gets wedged between rocks, said the French Space Agency's Julien Baroukh.
Once the rover's solar panels are deployed, the vehicle can no longer right itself, he added, which is why it will move at a glacial one millimetre per second.
Idefix will serve as a "scout for safety," according to Baroukh, as it prowls around Phobos for 100 days.
The lander will spend just two hours on Phobos, drilling and vacuuming up material, before launching back into space.
It will study Deimos during a series of flybys before leaving the Martian neighbourhood in 2030 and hustling back to Earth for a 2031 sample delivery in the Australian desert.
It's a treacherous undertaking, with wreckage littering the path but scientists hope to learn how Mars' 2 moons formed
Russia stumbled in all three of its Phobos attempts as well as many other Mars endeavours.
In its only other Mars mission, Japan failed to get a spacecraft into orbit around the red planet. Even NASA has had its share of flops in a bid to answer the burning question: Did life ever exist on Mars?
By studying Mars' moons, scientists hope to learn whether Phobos and Deimos formed in the aftermath of an ancient collision between Mars and a battering space rock. It's also possible that the moons might be stray asteroids that became ensnared in Mars' gravity.
Either way, scientists anticipate finding traces of Mars on Phobos, making the samples an irresistible two-for-one that should help demystify planetary and moon formation, and perhaps even the recipe for life.
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