Japan's space agency, JAXA, has launched the MMX spacecraft toward Phobos, the largest of Mars's two moons. The mission aims to become the first to land on Phobos and return samples from the Martian system to Earth, with at least 10 grams of material to be brought back.
The spacecraft lifted off at 04:41:03 on October 20, Japan time, which corresponded to the evening of October 19 in mainland Spain. The H3 rocket, flying on its tenth mission, departed from the Tanegashima Space Center. JAXA's launch result report says the probe separated from the rocket 71 minutes and 13 seconds after liberation and then settled into its planned orbit. The rocket left from the Yoshinobu launch complex, which the agency reserves for the H3, and JAXA reported that the vehicle flew as planned until release.
The European Space Agency, a mission partner, welcomed the launch. ESA's Director of Science, Carole Mundell, congratulated «JAXA and the entire MMX team» in the agency's statement. JAXA leads the mission together with NASA, France's CNES, Germany's DLR and ESA, which describes its role as a mission of opportunity on a project headed by another country.
The spacecraft weighs about 4,200 kilograms with fuel, according to ESA's technical summary. It is built from three modules. The propulsion module carries the probe to Mars using chemical engines and controls its orientation. The return module carries the main antenna, two solar wings and a dedicated 500-newton engine. The exploration module is the part that will land on the moon. It has four legs, two sampling systems and several of the mission's eleven scientific instruments.
Before the main landing, MMX will release a small rover called Idefix onto Phobos. CNES and DLR built the rover to explore the surface. According to ESA, Phobos's gravity is so weak that Idefix would weigh about 15 grams there compared with its weight on Earth, which makes landing and moving on the moon one of the mission's major technical challenges.
JAXA has prepared a core sampler that will extract material to a depth of 2 centimeters. NASA is contributing the P-Sampler, which lifts surface dust with pressurized nitrogen jets. The return capsule measures about 60 centimeters and has a heat shield to survive atmospheric entry. It is due to land in Australia and will then be transported to JAXA's ISAS institute in Sagamihara, near Tokyo.
Phobos and Deimos are named after the sons of Ares, the Greek god of war. According to ESA, almost everything known about them so far comes from a handful of flybys. NASA's MMX science lead, Tom Statler, described the central debate in the agency's statement: the moons could be remnants of a massive impact on Mars or ancient asteroids that the planet captured. To help settle the question, NASA is providing the MEGANE spectrometer, which will measure neutrons and gamma rays from the surface to determine the elements it contains. NASA will keep about 15 percent of the sample at the Johnson Space Center in Houston.
JAXA has already completed a round trip with the Hayabusa2 probe, which returned samples from an asteroid. ESA has supplied the transponder and amplifier that allow the spacecraft to communicate with Earth, and its Estrack station network will send commands to the probe and receive its data. Elliot Sefton-Nash, the ESA project scientist, said the teams are «even more motivated» to prepare for arrival at Mars next summer. The schedule sets arrival at Mars for August 2027 and orbit insertion around Phobos in September. The spacecraft is expected to spend roughly three years near Phobos and return the sample in Japanese fiscal year 2031.
No agency has yet fixed an exact date for sample collection, and the official statements do not specify the point on Phobos where the spacecraft will land. NASA updated its statement to adjust the timeline and now refers to 2028 at the earliest. NASA's science mission chief, Nicky Fox, said she expects the samples to produce science that will change paradigms, a result that will only be verifiable when the capsule returns in 2031.