JAXA, Japan’s national space agency, has just approved a robotic mission to visit the Martian moons Phobos and Deimos and retrieve a small sample from the former to bring back to Earth.

The mission plan: It’s called Martian Moon eXploration, or MMX. JAXA currently plans to launch MMX in 2024 and make it to the Martian system the following year. MMX will spend three years in the system studying and mapping the moons. The mission will make use of 11 different instruments, including a NASA-funded instrument called MEGAE that will measure the elemental composition of both bodies (perhaps revealing signs of ancient water).

The mission will also deploy a small rover to zip around the surface of Phobos, not unlike what JAXA’s Hayabusa2 mission deployed on the surface of the asteroid Ryugu.

Bringing home the Phobos dust: This is the mission’s marquee event. The four-legged MMX will attempt to land on Phobos and scoop up at least 10 grams of material from the surface, using a geological core sampler that can dig at least two centimeters deep.

It may seem a long way to travel to come back with such a tiny piece of the Martian system, but it’s actually a hundred times more material than Hayabusa2 is bringing back from Ryugu. If MMX is successful, it will return to Earth in 2029, completing the first round-trip mission to Mars and back.

What can we learn: Phobos is one stressed-out space rock. It’s only 3,700 miles away from Mars, and gravitational forces are literally tearing it apart (Earth’s moon is about a quarter-million miles from us). Phobos might finally crumble in 30 to 50 million years, and data from MMX could help give us a better idea of how its slow destruction will play out.

The mission could also go some way to solving one of the biggest mysteries of Mars’s two moons: where they came from. Phobos and Deimos are both small, oddly shaped, and in strange orbits (Phobos makes three laps around Mars a day). Researchers have long wondered whether they’re captured asteroids or leftovers from a giant impact event on their host planet, like Earth’s moon. We know Mars was once awash with water, and MMX’s sample could give us clues as to the fate of all that moisture.

Launch pad: Depending on whom you ask, humans might not be far behind MMX in venturing to Mars’s vicinity. Phobos has long been suggested as a potential stepping-stone to traveling to the Red Planet, and data from JAXA's mission might give us a better idea as to whether setting up shop on the Martian moon makes sense.