Japan’s sample return mission to Phobos may also collect some Mars dust

For decades, scientists have dreamed of getting Martian rocks into Earth’s laboratories — a Herculean feat that would revolutionize our knowledge of the Red Planet. An audacious mission from the Japanese space agency might offer the next best thing: rocks from Mars’ larger moon, Phobos. That’s the task confronting the Martian Moons eXploration (MMX) spacecraft, due to launch October 19 at 3:41 p.m.

The mission aims to crack the long-standing mystery of how Mars got its two odd moons by delivering a sample of Phobos to Earth in 2031. These rocks are no substitute for true Martian material — but given that NASA’s plans to fetch the Perseverance rover’s prized samples are in limbo, scientists are eager for even an indirect glimpse of Mars. Three previous spacecraft from Russia failed.

The MMX itinerary is action-packed: After launch, the spacecraft will spend about one year cruising out to Mars, then slip into orbit around Mars alongside Phobos for about three years. During its stay, the spacecraft will deploy a small rover named Idefix to scout the moon for good sampling sites. The main spacecraft will then make two landings to grab 10 grams of sample, about the weight of four U.S. pennies.

It will use two different devices to snag the sample: One will drill two centimeters down into the rock, while the other will blow pressurized gas at the surface to collect loose material. Once loaded up, MMX will zip past the smaller moon Deimos before making the one-year trek home to drop its cargo in Australia’s outback, just as Japan’s two previous asteroid sample-return missions have done. After the Japanese space agency JAXA sorts and catalogs the samples, it will share portions of them with other institutions.

Such a small handful of rock may not sound impressive, but it’s enough to thrill researchers. MMX is designed to reveal the enigmatic origins of Phobos and Deimos — the only moons in the inner solar system besides our own. The strange objects look like rocks that wandered in from the outer asteroid belt and got trapped around Mars.

But their tidy circular orbits suggest they coalesced after a massive collision tore material off the Red Planet. Or perhaps they came about some other way that scientists simply haven’t imagined, says planetary scientist Kiyoshi Kuramoto of Hokkaido University in Sapporo, Japan. Studying the features and composition of Phobos’ surface could solve the mystery.