Scientists don’t know how Mars got its two moons, and a new probe is on its way to find out

Mars has two small moons, Phobos and Deimos, with Phobos being the larger of the two. For a long time, scientists have argued about how they ended up circling the Red Planet. This is because there is a lack of data that explains their origins. And despite their potential importance, neither moon has ever been fully investigated.

Now, Japan’s space agency, JAXA, has launched a mission to study these moons and finally solve the mystery of how they formed. Here’s what we know so far about Mars’s moons and what lies ahead.

Japan’s space agency (JAXA) has recently launched its Martian Moons eXploration (MMX) probe from the Tanegashima Space Center on October 20, 2026. NASA, the European Space Agency, France’s National Center for Space Studies, the German Aerospace Center and the Australian Space Agency have all contributed to this project. 

Commenting on the significance of the moons, project manager Yasuhiro Kawakatsu explained, “They are known as the most important unclimbed mountains in the solar system.”

As of now, there are two leading theories. One says that something huge might have hit Mars and flung its material into space, which then clumped together into the moons. That is also roughly how Earth’s moon is thought to have formed. 

But this theory doesn’t explain why the debris would form two small moons instead of one big one. The other idea says the moons were asteroids that Mars captured into its orbit millions of years ago.

Each theory points to a different story. If Phobos really came from Martian debris, it could hold material from Mars’ earlier days, when the planet may have been better suited to hosting life than it is now. 

And if it came from the outer solar system, it may have carried water-bearing minerals and organic compounds. Those could have helped life begin on Earth.

As per JAXA, the MMX spacecraft is expected to reach the Mars system in 2027. It will then collect its sample no earlier than 2028 and deliver it to Earth in 2031. Phobos is the closest moon to Mars, so it has likely been sprayed with debris from asteroid impacts on the planet. 

Scientist Kiyoshi Kuramoto estimates only about 1 percent of the sample may be Martian, but he is hopeful: “I do think there’s a possibility that chemical traces of biological activity might be contained within that sand sample.”