Japan's Mars Moons Exploration Mission Set to Launch for Phobos Sample
The MMX spacecraft is due to launch on Monday from Japan and reach Phobos in August 2027 to collect about 10 grams of Martian moon material
By AXY Science Desk ·
Key points
- Japan's MMX mission is set to launch on Monday to collect about 10 grams of material from Phobos and bring it back to Earth.
- If successful, MMX would be the first time a sample from Mars or its moons has been returned for analysis in laboratories on Earth.
- The spacecraft is due to arrive at Phobos in August 2027 and will study Deimos along the way.
- Scientists hope the sample will help explain how Mars's moons formed, a question still debated among researchers.
- Landing a rover on a moon as small as Phobos has never been done, partly because of its very weak gravity.
Japan's Mars Moons Exploration mission, known as MMX, is set to launch on Monday from Japan on an ambitious attempt to collect a piece of Phobos, one of the two small moons that orbit Mars, and bring it back to Earth. The mission aims to return about 10 grams of Martian moon dust. If it succeeds, it would be the first time a sample has been returned from Mars or its moons to be analysed in laboratories on Earth. The mission is led by the Japanese Space Agency, and the spacecraft is due to arrive at Phobos in August 2027. Its backers hope the material will help solve the mystery of how Mars's moons formed.
What the mission is designed to do
MMX is a sample-return mission, which means it must do much more than observe a distant object from afar. The spacecraft has to travel across space to a small, weakly held world, collect material, store it safely, and carry it back to Earth. Each stage carries technical risk. A sample-return mission is harder than a flyby or an orbiter because the spacecraft must interact physically with the target and then survive a long journey home with its cargo intact.
According to the BBC's report, MMX will first study Deimos, the other small moon of Mars, as it arrives in the Mars neighbourhood. It will then focus its attention on Phobos. The mission also plans to set down a small rover to explore the terrain. The rover is intended to look at the surface directly, but landing it is considered extremely difficult because of the unusual nature of the target. Even so, the goal of the mission is clear: to bring physical material from a Martian moon to a laboratory where scientists can examine it in detail.
Two tiny moons with a big question
The BBC reports that there are only three moons in the inner Solar System: Earth's own Moon, and two that circle Mars, called Phobos and Deimos. Both Martian moons are very small by planetary standards. Phobos is about 20 kilometres (12 miles) across, and Deimos is about 10 kilometres (six miles) across. Both are irregularly shaped, which led the BBC to describe them as looking a bit like space potatoes. Phobos and Deimos were discovered in 1877 and have been studied ever since, largely through images and data gathered by spacecraft orbiting Mars.
The central scientific puzzle is where the moons came from. Researchers have long debated two broad explanations. One idea is that both moons are captured asteroids that drifted into orbit around Mars. The other is that they formed from debris left after a large impact on Mars early in its history. The two explanations would leave different traces in the composition and internal structure of the moons, which is why detailed analysis of real material could be so valuable. Remote instruments can reveal a surface's broad features, but laboratory instruments on Earth can examine a physical sample in far greater detail, including its chemistry and the age of its minerals.
The BBC report says the mission is hoped to solve how Mars's moons formed. Its success would not settle every question about the Martian system, but it would give scientists a physical object to test competing ideas against.
Why bringing a sample home matters
Returning material from space has produced some of the most important results in planetary science. Apollo missions brought lunar rock and soil back to Earth in the early 1970s. Japan's Hayabusa2 spacecraft returned samples from the asteroid Ryugu in 2020. In each case, laboratory work on the returned material allowed scientists to test ideas about age, chemistry and history in ways that remote observation alone could not.
Scientists already have some Martian material to study. Meteorites found on Earth are widely accepted to be rocks that were blasted off Mars by impacts and later landed on our planet. However, these fragments arrive by chance, and the exact part of Mars they came from is often uncertain. A sample collected deliberately from a known location, under controlled conditions and with careful records, would give researchers much firmer context. That is one reason the MMX mission is drawing attention beyond the Japanese space community.
The mission also has practical value for future work. Learning how to approach, touch down on, collect material from and depart from a very small body would be useful for later missions to similar objects. Analysts expect that the lessons from MMX could influence how space agencies plan sample collection around targets with weak gravity, although any such influence will depend on how the mission performs.
The difficulty of landing on a tiny moon
The rover element is one of the most challenging parts of the mission. Prof Sara Russell, from the Natural History Museum, who is the MMX mission's deputy for sample analysis, said that no one has ever landed a rover on a moon as small as Phobos. Her explanation focused on gravity: "The moon itself doesn't have very much of its own gravity," she said.
Weak gravity may sound like it makes landing easier, but it creates its own problems. On a body with very little gravitational pull, a spacecraft or rover cannot rely on the forces that keep objects settled on a planet's surface. Anything that touches down may bounce, drift or fail to anchor properly. Motion has to be managed with great care, and the same weakness that complicates landing could also make it difficult to lift off again. Engineers and mission planners must solve these problems before the spacecraft reaches Mars, because there is little opportunity to correct them once the spacecraft is far from Earth.
The irregular shape of the moons adds another layer of difficulty. A surface that is not a smooth sphere can change the way a landing site looks and behaves, and that can complicate navigation during the final approach. These are not problems that can be fully tested on Earth, which is why each stage of the mission carries significant uncertainty.
Expert view and what happens next
Russell described the mission in strongly positive terms while also acknowledging how untested it remains. "There hasn't yet been a successful mission to go to Phobos and bring a bit back to Earth," she said. "I think this is an incredibly ambitious and fun mission," she added.
The immediate milestone is the launch, which is scheduled for Monday from Japan. After that, the spacecraft must travel to the Martian system and reach Phobos by August 2027. Along the way, it will study Deimos before concentrating on Phobos. Observers are likely to watch several key stages: the launch itself, the spacecraft's arrival at Mars and Deimos, the approach to Phobos, the attempted rover landing, the collection of material, and the eventual journey home. The BBC report does not give a date for the sample's return to Earth, so the timeline after arrival at Phobos remains an important open question.
If MMX succeeds, the material could help settle one of the longest-running questions about Mars's moons and offer a rare, direct look at the Martian system. If it falls short, the mission would still produce data about the technical challenges of working near tiny, irregular worlds, which could help future missions. Either outcome is likely to be followed closely by planetary scientists, who have been waiting for a chance to study Phobos up close and bring material back for detailed examination.
Questions and answers
What is the Mars Moons Exploration mission?
MMX is a mission led by the Japanese Space Agency that is set to launch on Monday from Japan to collect a sample from Phobos, one of Mars's two small moons, and bring it back to Earth.
When will the MMX spacecraft reach Phobos?
The spacecraft is due to arrive at Phobos in August 2027. It will first study Deimos, the other Martian moon, as it arrives in the Mars neighbourhood.
Why does the Phobos sample mission matter?
If successful, it would be the first time a sample from Mars or its moons has been returned to Earth for laboratory analysis. Scientists hope it will help explain how Mars's moons formed.
How big are Phobos and Deimos?
Phobos is about 20 kilometres (12 miles) across and Deimos is about 10 kilometres (six miles) across. Both are irregularly shaped.
Topics: Mars Moons Exploration, MMX mission, Phobos, Deimos, Mars, Japanese Space Agency, Sample return, Natural History Museum
Sources: BBC Science