# 【取材報告】火星の衛星探査機、打ち上げ成功（林公代） - Show: 荻上チキ・Session～発信型ニュース・プロジェクト - Published: 2026-10-20 - Canonical: https://podc.club/en/episode/1532201544_789123888f89.html - Audio: https://pdst.fm/e/pscrb.fm/rss/p/traffic.megaphone.fm/TBS4694342407.mp3 - Source: Edited from a machine transcript of the first 30 minutes of the episode. Not an official summary. In the early hours of October 20, 2026, Japan's H-3 rocket No. 10 lifted off from Tanegashima Space Center and successfully placed the Martian Moons eXploration spacecraft MMX into its planned orbit. MMX is bound for Phobos, the potato-shaped moon of Mars, where it will land, collect surface samples, and return them to Earth in July 2031. If the mission succeeds, it will be humanity's first sample return from Martian space. ## What this episode answers ### What is MMX's mission, and why is it called a world first? MMX is a Japan-led international mission to land on Phobos, collect samples, and return them to Earth in July 2031—making it humanity's first sample return from Martian space, since no material from Mars or its moons has ever been brought back. ### What was it like to witness the launch on the ground? Space writer Hayashi Kimiyo (林公代) watched from the press seats at Takesaki Observatory inside Tanegashima Space Center; she described an intense light rising steadily through a cloudless, star-filled sky, with vibrations strong enough to make her legs shake. ### What scientific insights can be gained from analyzing Phobos samples? Phobos samples could settle the debate over the moon's origin—impact-debris formation versus gravitational capture of a passing asteroid—and provide clues about how water was transported to early Mars. ### What technical challenges does landing on Phobos and returning to Earth involve? One-way communication delays of 15–20 minutes force the spacecraft to operate almost entirely autonomously for obstacle avoidance, landing, drilling, and departure; it must also contend with Mars's powerful gravity during the landing and complete Japan's first-ever Mars orbit insertion on the return leg. ### How is MMX connected to future crewed Mars exploration? Phobos is considered a leading candidate for a forward base in support of crewed Mars missions under the Artemis program; MMX will also survey the radiation environment around Phobos, contributing directly to the safety preparations required before humans can go there. ## Article ## H-3 in Its Most Powerful Configuration Thunders Over Tanegashima In the early hours of October 20, 2026, H-3 rocket No. 10 lifted off from Tanegashima Space Center in Kagoshima Prefecture. The vehicle flew in what engineers call the "24 configuration"—H-3's most powerful form, fitted with four solid rocket boosters. Approximately 70 minutes after liftoff, the rocket successfully delivered the Martian Moons eXploration spacecraft MMX to its planned orbit. Space writer Hayashi Kimiyo (林公代), reporting from the press seats at Takesaki Observatory inside the launch complex, described the scene: "There were no clouds, and under a sky full of stars, an intense light like the sun rose steadily and stayed visible for a long time. The vibration reached us and my legs were trembling from the shockwave." ## What Is MMX—The World's First Sample Return from Martian Space MMX (Martian Moons eXploration) is a Japan-led international mission. Its objective is a sequence no spacecraft has ever completed: land on Phobos, one of Mars's two moons, collect surface samples, and return them to Earth. If everything goes to plan, the samples will arrive in July 2031—the first time any material from Martian space has been brought back to Earth. Phobos is a small, potato-shaped body roughly 22 km across, orbiting Mars at the remarkably close distance of about 6,000 km. The science team requires MMX to collect at least 10 grams of material. "That may sound like a tiny amount," Hayashi noted, "but as a returned sample it is actually quite substantial." ## Two Mysteries Written in Phobos Dust Scientists expect two major discoveries from the Phobos samples. The first concerns the origin of Phobos itself. Two competing theories exist: the impact hypothesis—that Phobos coalesced from debris thrown up when a large body struck Mars—and the capture hypothesis—that it was a small object from farther out in the solar system snared by Mars's gravity. Mineral analysis of the returned sample should help determine which is correct. The second concerns the origin of Mars's water. Early Mars is thought to have had vast oceans, yet no liquid water exists there today. Phobos samples may carry clues about how water was transported within the solar system and delivered to Mars, shedding light on a broader question about planetary formation. ## Autonomous Landing Under a 15-Minute Communication Delay Japan pioneered small-body sample return with Hayabusa and Hayabusa2, but MMX faces challenges on an entirely different scale. The dominant difficulty is Mars's gravity. Because Phobos orbits only about 6,000 km from Mars, the spacecraft will feel that gravitational pull throughout the entire landing sequence. Compounding the problem, one-way communication delays between Earth and the spacecraft will be 15 to 20 minutes, meaning almost every decision—from obstacle avoidance to the final touchdown call—must be made autonomously by MMX itself. "There is only one exchange possible with the ground," Hayashi explained. "After that, the spacecraft makes every call on its own." Hayabusa's method of touching down momentarily to capture particles and immediately departing will not be sufficient here. MMX must achieve a full landing on Phobos, use a drill-like device to retrieve material from roughly 2 cm beneath the surface, then lift off again and stow the sample securely in its return capsule—a far more complex sequence of operations. ## The Gauntlet on the Way Home—Mars Orbit Insertion and a Streamlined Return The return journey brings its own series of hurdles. The first major milestone is Mars orbit insertion, scheduled for around August or September 2027. Japan has never successfully inserted a spacecraft into Mars orbit—the earlier probe Nozomi failed at this stage—and the maneuver requires a precisely timed, extended retroburn within only a narrow window. After entering Mars orbit, MMX will spend three years conducting two separate landings on Phobos to collect samples from different locations. On the journey home, the spacecraft will be shed in three stages to conserve fuel, until only the return module continues toward Earth. Near Earth, the sample capsule will be separated from the module and will land in the Woomera desert in Australia for recovery. ## "The Solar System's Most Important Unexplored World" as a Stepping Stone to Crewed Mars Despite attempts by several nations including Russia, no mission has ever successfully explored Phobos, earning it the description "the most important unexplored body in the solar system." Crewed Mars exploration is a long-term goal of the Artemis program, in which both NASA and Japan participate, and Phobos is considered a leading candidate for a crewed forward base. MMX will also survey the radiation environment around Phobos—data essential for establishing the safety of any future human mission to the area. "If MMX succeeds," Hayashi said, "it will be an enormously important achievement for the world and a demonstration of Japan's technological capabilities." ## Takeaways - H-3 rocket No. 10 successfully launched MMX on October 20, 2026, beginning a five-year mission to achieve the world's first sample return from Martian space, with Earth return targeted for July 2031. - Phobos samples are expected to resolve two major scientific questions: the moon's origin—impact debris versus gravitational capture—and the source of the water that once filled Mars's ancient oceans. - With one-way communication delays of 15–20 minutes, MMX must operate near-autonomously through landing, drilling, and departure, and must complete Japan's first-ever Mars orbit insertion before the samples can head home.