The spacecraft will reach Mars in 2027 and return its sample capsule to Earth in 2031.
Japan's space agency JAXA has launched the Martian Moons eXploration mission on an H3 rocket from the Tanegashima Space Centre, aiming to bring back the first samples from Phobos, the larger of Mars's two moons.
The spacecraft is expected to reach the Martian system in August 2027. It will study Phobos in detail, fly past the smaller moon Deimos and land on Phobos around 2029-30 to collect at least 10 grams of surface material.
It also carries IDEFIX, a small French-German rover that will explore the surface and help assess landing sites.
The sample capsule is due back on Earth in 2031. Scientists hope the material will reveal how Mars's moons formed. The mission costs about $578 million.
