Japan has launched an ambitious space mission to explore the two moons of Mars, aiming to collect samples from one of them and bring them back to Earth for scientific examination. The mission is expected to provide fresh insights into the origins of the moons and potentially uncover clues about whether Mars once supported life.
The Japan Aerospace Exploration Agency (JAXA) launched its Martian Moons eXploration (MMX) spacecraft on October 20 from the Tanegashima Space Centre in southern Japan. The spacecraft will undertake a year-long journey towards Mars, where it plans to land on Phobos, the larger of the planet’s two natural satellites, and collect at least 10 grams of rock and dust. The samples are expected to return to Earth in 2031.
The mission is considered a significant step in planetary exploration, as several spacecraft, landers and rovers have previously travelled to Mars, but no mission has yet brought back samples from the planet or its moons. Scientists believe that material collected from Phobos could help answer longstanding questions about how the two moons were formed.
Phobos and Deimos, the two moons of Mars, are relatively small celestial bodies measuring approximately 22 kilometres and 12 kilometres across, respectively. Their irregular shapes have often been compared to potatoes. One scientific theory suggests that they could be asteroids captured by Mars’ gravitational pull. However, this explanation does not fully account for their nearly circular orbits around the planet’s equator. Captured asteroids generally follow more elliptical and tilted orbital paths.
An alternative theory proposes that the moons were formed following a massive collision involving Mars. According to this explanation, a large impact scattered debris into space, which subsequently came together under gravitational forces to form the two moons. Scientists hope that an examination of Phobos’ composition will help determine which of these theories is more likely.
JAXA has been developing the MMX mission for more than a decade, with technical and scientific cooperation from space agencies in the United States, Europe and Australia. The project builds on Japan’s earlier achievements in retrieving samples from asteroids. Its Hayabusa mission successfully brought back grains from the asteroid Itokawa in 2010, while the Hayabusa2 spacecraft returned five grams of material from asteroid Ryugu in 2020, exceeding its original collection target.
Analysis of the earlier samples revealed water-bearing molecules and organic compounds, providing valuable information about the possible role of asteroids in delivering some of the basic ingredients necessary for life to Earth.
However, the new mission presents considerably greater technical challenges. Phobos has a surface gravity approximately one-2,000th that of Earth, but it is around 40 times stronger than the gravity on Ryugu. This difference makes landing and operating a spacecraft on its surface more complicated. Unlike the earlier Hayabusa missions, which briefly touched asteroid surfaces to collect material, MMX is designed to land on Phobos and retrieve samples from beneath its surface.
The spacecraft will also carry out several scientific investigations during its approximately three-year operations around Mars. One of its key instruments, MEGANE, developed by NASA, will examine gamma rays and neutrons released when cosmic rays strike Phobos. The measurements will help scientists determine the moon’s chemical composition. In addition, a small European-built rover will explore the surface and collect information about its physical characteristics.
Scientists believe the mission could have implications beyond understanding the formation of the moons. Because of its proximity to Mars, Phobos may contain material ejected from the planet during asteroid impacts. Researchers estimate that Martian material could account for around 0.1 per cent of the samples collected during the mission.
Although scientists have previously studied meteorites originating from Mars, most of these are volcanic rocks that managed to survive the journey through space and Earth’s atmosphere. Researchers are particularly interested in recovering sedimentary material, which could preserve evidence of the planet’s ancient environmental conditions.
Sara Russell, a planetary scientist at London’s Natural History Museum who will participate in analysing the samples, believes that such material could potentially contain biosignatures, or chemical and physical indicators associated with past life.
Evidence from ancient river channels and lake deposits suggests that Mars once had flowing water and a considerably thicker atmosphere. Scientists are investigating whether these conditions could have made the planet suitable for microbial life in its distant past.
Researchers also believe that Phobos and Deimos may have preserved material from Mars’ early history because their surfaces have undergone relatively little geological transformation. Their composition could therefore offer a glimpse into conditions that existed billions of years ago.
If successful, Japan’s mission could significantly advance understanding of Mars, its moons and the early history of the solar system, while bringing scientists closer to answering one of the biggest questions in space exploration: whether life ever existed beyond Earth.
