Japan's MMX Mission Is Set to Grab a Piece of Mars's Moon Phobos

A Japanese spacecraft is about to head into deep space on a bold mission — to grab a small piece of Mars's moon Phobos and bring it back to Earth. The mission is called Mars Moons Exploration, or MMX, and it is led by the Japanese Space Agency. It is set to launch from the Tanegashima Space Center in Japan on October 20, 2025. If it succeeds, it will be the first time ever that material from Mars or its moons has been returned to Earth for scientists to study.

Mars has two tiny moons called Phobos and Deimos. Both are very small and oddly shaped — scientists say they look a bit like space potatoes. Phobos is about 20 kilometers across, while Deimos is about 10 kilometers across. These are the only moons found in the inner Solar System besides Earth's own Moon.

The MMX spacecraft is expected to arrive near Mars in August 2027. It will first study Deimos before turning its full attention to Phobos. One of its first jobs will be to drop a small rover onto the surface of Phobos to explore the terrain. No spacecraft has ever landed a rover on such a tiny moon, making this an extremely difficult challenge.

Landing on Phobos is tricky for a surprising reason. The moon has very little gravity of its own because it is so small, but it sits right next to Mars, which has a much stronger pull. Prof. Sara Russell from the Natural History Museum explained that this mix of weak and strong gravity nearby makes it very hard to safely land a rover. The rover's job will be to scout out a good spot for the main spacecraft to touch down.

Once the MMX spacecraft lands, it will use a robotic arm and two special samplers to collect moon dust from the surface. That dust will be packed into a small sealed capsule. The capsule will then travel back to Earth and land in the Woomera desert of South Australia in 2031. The full journey — from Earth to Phobos and back — will take around six years.

The amount of material coming back is tiny — only about 10 grams, roughly the weight of two teaspoons of sugar. Dr. Chrysa Avdellidou from Leicester University says that even though it sounds like very little, scientists can do a great deal with it. They can study individual grains using powerful lab equipment to learn about the moon's history. As she put it, 'You don't need to have kilos back from a surface in order to do science. So it's worth every gram.'

Scientists are not sure yet how Mars's moons formed, and there are two leading ideas. One idea is that a large rock crashed into Mars long ago, and the leftover debris slowly became Phobos and Deimos. The other idea is that the two moons are actually asteroids captured by Mars's gravity as they drifted through space. The chemical makeup of the returned sample should quickly reveal which idea is correct.

There could also be a surprising bonus hidden in the sample. Because Phobos orbits very close to Mars, tiny bits of Martian rock may have been blasted off the Red Planet by asteroid strikes and landed on Phobos over billions of years. That means the sample might contain actual grains of Mars itself. This would give scientists a rare, direct look at the history and makeup of Mars.

Getting a fresh sample from Mars has been a dream of space scientists for decades. NASA's Perseverance rover has been collecting rock samples on Mars since 2021 and storing them in sealed canisters, but a planned mission to return those canisters to Earth was cancelled after funding was stopped. China is also working on a Mars sample mission set to launch in 2028. Meanwhile, MMX remains the closest thing scientists have to a real Mars sample return mission right now.

Scientists already have some Martian material on Earth in the form of meteorites — rocks blasted off Mars by ancient impacts that fell to our planet. However, these meteorites mix with Earth's air, water, and soil as soon as they land, making them contaminated. A sample sealed inside the MMX capsule would arrive completely pristine and untouched. That is exactly what makes this mission so valuable to researchers around the world.