Japan Launches a Six-Year Mission to Grab a Piece of Mars's Moon

Japan is about to do something no country has ever attempted: fly to Mars, land on one of its moons, and bring a Piece of Mars's Moon back to Earth. The Martian Moons eXploration spacecraft, built by the Japan Aerospace Exploration Agency, is scheduled to lift off today from the country's Tanegashima Space Center at 3:41 p.m. Eastern time, beginning a round trip that will not end until a capsule parachutes into the Australian outback five years from now.

The launch window opens this afternoon on a Japanese heavy-lift rocket, with the space agency streaming the liftoff live in Japanese and English starting about an hour beforehand, according to BBC Sky at Night Magazine. If weather or a technical snag scrubs the attempt, the schedule can slip inside a window that stays open into early November, as reported by ecoticias. The agency confirmed the date in August, and Europe's space agency reaffirmed it earlier this month.

The long round trip, in five stops

The journey is choreographed in stages. After liftoff, the probe cruises for roughly ten months and arrives in the Mars system in the summer of 2027. It will then spend more than a year surveying Phobos and its smaller sibling Deimos from a special orbit that keeps it hovering near the moon while circling the planet. Touchdowns for sampling begin no earlier than the end of 2028. The spacecraft departs the Mars system in 2030, and its return capsule is due to land at Woomera in South Australia in 2031.

That patience is deliberate. Phobos is a battered, potato-shaped rock about fourteen miles across, and landing on it is nothing like landing on our own Moon. Its gravity is roughly one thousandth of Earth's, so a spacecraft cannot really land so much as rendezvous and gently touch down. The surface has never been explored up close, and every command from Earth takes up to forty-four minutes to make the round trip, which means the probe must handle the trickiest moments on its own.

The rover goes first

Before the main spacecraft attempts its touchdowns, it will deploy Idefix, a 55-pound rover built by the French and German space agencies. Idefix becomes the first rover ever to drive on a moon of Mars, and it will spend about three months scouting the surface and helping engineers pick safe sampling sites. JAXA's international outreach lead for the mission, Elizabeth Tasker, says the survey phase uses a suite of remote-sensing instruments to map the moon before anyone commits to a touchdown spot.

The sampling itself uses two different tools. A Japanese coring device will bite about two centimeters into the surface, while a NASA-supported pneumatic system fires pressurized gas to blow loose material into a collection tube. The goal is at least 10 grams of Phobos soil and rock. Ten grams sounds like almost nothing, and it is: roughly two sugar packets. But the mission's scientists argue that even a thimbleful of another world is enough to rewrite textbooks, and history backs them up.

Why a handful of dust is worth the trip

The central mystery is where Phobos came from at all. One camp of planetary scientists believes the moon is debris blasted off Mars by a giant impact long ago; another believes it is a captured asteroid that wandered too close and never left. The returned grains should settle the argument, because their chemistry will point one way or the other. There may even be a bonus: Martian rock knocked off the planet by ancient impacts is expected to be sitting on the surface, so the capsule could deliver the first Mars sample ever returned to Earth without ever touching Mars itself.

Small samples have an outsized record. Grains returned from the asteroid Ryugu by Japan's earlier Hayabusa2 mission turned out to contain all five of the basic chemical letters of DNA and RNA, a discovery no orbiting instrument could have made. "Bringing samples to our most sophisticated labs here on Earth is a multiplier for discoveries, because our most precise instruments are too large, complex or sensitive to send to space," the mission's European project scientist, Elliot Sefton-Nash, told Impactful Ninja. Samples, he added, are the gift that keeps on giving, since future generations will study them with instruments that do not exist yet.

The crowded race for Mars rocks

The timing matters beyond Japan. NASA's own plan to bring home rocks cached by its Perseverance rover has stalled amid budget and design fights, and China is aiming to return its own Mars samples around the same year MMX comes home. That makes this mission the most likely candidate to deliver the first-ever material from the Mars system to a laboratory, a milestone decades in the making. The international lineup behind it, spanning Japan, the United States, Europe, France and Germany, also makes it one of the most collaborative deep-space missions ever flown.

For skywatchers and space fans, today is the easy part: watch a rocket climb, then settle in for the long haul. If all goes to plan, the payoff arrives early next decade, when a small capsule carrying a Piece of Mars's Moon streaks over the outback and a half-decade of patience turns into a few grams of the most traveled rock in the solar system. More science coverage: great white sharks are back off California, and ancient Roman passages are opening beneath Hagia Sophia.

Sources: a BBC skywatching magazine's launch preview; a detailed rundown of the launch schedule and mission hazards; a breakdown of the science case.