By Takuya Muraoka and Hiroyuki Oyama / Yomiuri Shimbun Staff Writers

20:00 JST, October 21, 2026

Japan’s Martian Moons eXploration (MMX) probe began a long journey on Tuesday, with its outbound trip to exceed 500 million kilometers. Will the mission, which aims to deliver samples from the Martian moon Phobos to Earth, shed light on how the solar system was formed? The next five years will put Japanese technology to the test.

The ambitious MMX project will take about two years for the trips to the neighborhood of Mars and back, and about three years for exploration. “The long journey toward humanity’s first sample returned from near Mars has begun,” Hiroshi Yamakawa, president of the Japan Aerospace Exploration Agency (JAXA), said at a press conference on Tuesday.

Phobos, which is one of two moons that orbit Mars and has an altitude of about 6,000 kilometers, is a small celestial body with a diameter of 20 to 30 kilometers. MMX will land on this moon to collect samples that will be analyzed to investigate how Phobos was formed.

There are two leading hypotheses for the origin of Phobos. One is the “asteroid capture hypothesis.” According to this hypothesis, an asteroid that was flying by Mars was captured by the planet’s gravity and became a moon. The........

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