NASA to Help Unlock Mysteries of Mars’ Moons in Upcoming Mission

Meta Title: NASA and Japan’s MMX Mission Aim to Solve the Mystery of Mars’ Moons

Meta Description: NASA is supporting JAXA’s Martian Moons eXploration mission, which will study Phobos and Deimos and attempt to return samples from Mars’ largest moon.

URL Slug: nasa-jaxa-mmx-mars-moons-phobos-deimos-sample-return

Excerpt: NASA is contributing to Japan’s MMX mission, an ambitious effort to investigate Mars’ moons Phobos and Deimos. By studying the moons up close and returning material from Phobos to Earth, scientists hope to determine how these unusual worlds formed—and what they can reveal about the early solar system and Mars itself.

# NASA Will Help Investigate the Origins of Mars’ Two Small Moons

Mars has two tiny, irregularly shaped moons: Phobos and Deimos. Unlike Earth’s large, nearly spherical Moon, these objects look more like dark, battered asteroids. Their unusual appearance has prompted a long-running scientific question: are they captured asteroids, or did they form from debris produced by a giant impact involving Mars?

NASA is supporting an upcoming mission led by the Japan Aerospace Exploration Agency, or JAXA, that could provide the clearest answer yet. The Martian Moons eXploration mission, known as MMX, is designed to study both Phobos and Deimos in detail and return a sample from Phobos to Earth.

The mission represents an important international effort in planetary science. JAXA is leading the spacecraft and planned sample-return operation, while NASA is contributing scientific expertise and hardware. The resulting data could reshape scientists’ understanding of Mars, its moons, and the processes that built the rocky planets.

## Why Phobos and Deimos Are Still a Mystery

Phobos and Deimos are among the smallest known moons in the solar system. Phobos, the larger of the two, is only about 27 kilometers across at its widest point. Deimos is smaller still, measuring roughly 15 kilometers across.

Both have dark surfaces and irregular profiles that resemble carbon-rich asteroids. That resemblance led to the idea that Mars may have captured them from the asteroid belt early in solar system history. However, that explanation has serious challenges.

Capturing an asteroid is difficult. A passing object would need to lose enough energy to become permanently bound to Mars without crashing into the planet or escaping back into space. Scientists have proposed possible mechanisms, including interactions involving Mars’ early atmosphere or multiple objects passing through the planet’s gravitational environment, but no single capture scenario fully explains the moons’ present orbits and compositions.

The alternative is that the moons formed closer to Mars. In this model, a large impact could have blasted rock from the Martian crust into orbit. That material may have formed a disk around the planet, eventually producing one or more moons. Over time, most of those moons could have fallen back to Mars or broken apart, leaving Phobos and Deimos as survivors.

A returned sample may be able to distinguish between those possibilities. Material with characteristics similar to Martian rocks would strengthen the impact-origin hypothesis. Material with chemical and mineral signatures associated with primitive asteroids could support a capture origin. The answer may also prove more complicated, with the moons containing a mixture of Martian and external material.

## What the MMX Mission Is Designed to Do

MMX is not simply a flyby mission. Its central objective is to investigate the Martian moon system from close range and collect material from Phobos for delivery to Earth.

The spacecraft is expected to conduct observations of both moons, mapping their surfaces and examining their geology, mineral composition, gravity, and surrounding environment. It will also study Mars from the moon system, including dust and other material moving through the region around the planet.

Phobos is the primary sampling target. The mission is intended to touch down on its surface, gather regolith—loose dust, grains, and fragments—and preserve it for a return journey to Earth. Laboratory analysis on Earth can be far more precise than measurements made by instruments on a spacecraft.

Scientists can examine tiny grains for isotopes, organic compounds, water-bearing minerals, and evidence of past alteration. They can also compare those samples directly with Martian meteorites and material collected from asteroids by sample-return missions.

That is why sample return is so valuable. A spacecraft can identify broad surface patterns, but Earth-based laboratories can test detailed questions that mission planners may not even have anticipated before launch.

## NASA’s Role in a JAXA-Led Mission

NASA’s participation in MMX builds on decades of collaboration between space agencies and research institutions. The agency is contributing the MEGANE instrument, short for Mars-moon Exploration with GAmma rays and NEutrons.

MEGANE will measure gamma rays and neutrons emitted from Phobos’ surface. Those emissions can help researchers estimate the abundance of elements and identify hydrogen-rich materials, which may indicate water or hydroxyl-bearing minerals. The instrument is intended to provide global compositional information, complementing the local material collected during surface sampling.

This broader view matters because a sample from one location cannot automatically represent an entire moon. Remote sensing can help scientists place the collected material in geological context: Was the sampling site typical? Does it sit near unusual terrain? Are there compositional differences across the surface?

NASA’s involvement also reflects the agency’s wider Mars exploration program. Orbiters, landers, rovers, and the Perseverance rover’s ongoing caching of Mars samples have transformed knowledge of the Red Planet. MMX adds a different perspective by examining material that may preserve clues to Mars’ earliest history beyond the planet’s own surface.

## What a Phobos Sample Could Reveal About Mars

Phobos may be more than a moon. Its surface could contain a natural archive of material from several sources.

If Phobos formed after a major impact on Mars, it may include ancient Martian debris. Such material could be older than much of the terrain accessible to current Mars surface missions. It might preserve evidence of the composition of Mars’ early crust or conditions during a formative period in the planet’s history.

Even if Phobos began as a captured asteroid, its surface has spent billions of years orbiting Mars. Small impacts and dust exchange may have deposited tiny amounts of Martian material there. A carefully analyzed sample could potentially include particles ejected from Mars by ancient impacts.

The moon’s surface may also record impacts from elsewhere in the solar system. That makes Phobos scientifically interesting as a possible collection point for dust and fragments that arrived from the asteroid belt, comets, and interplanetary space.

Researchers will need to separate these possible sources using mineralogy, elemental chemistry, and isotopic measurements. That work will be complex, but it is precisely the kind of analysis that becomes possible when physical samples are returned to Earth.

## Why Deimos Matters Too

Although Phobos receives much of the attention because it is the sample-return target, Deimos is equally important to the mission’s larger scientific goals.

The two moons share broad similarities, yet they differ in size, orbit, and surface features. Comparing them could reveal whether they formed through the same event, were captured separately, or experienced very different evolutionary histories.

Deimos orbits much farther from Mars than Phobos. Phobos, meanwhile, is gradually moving closer to Mars due to tidal interactions and is expected to eventually break apart or collide with the planet on geological timescales. Studying its structure and composition can help scientists understand how this long-term evolution is unfolding.

MMX observations of both moons will therefore provide a system-level view rather than treating Phobos as an isolated object.

## A Significant Step for International Sample Return

The mission also highlights the growing importance of international sample-return science. JAXA has already demonstrated the value of this approach through its Hayabusa and Hayabusa2 missions, which returned material from the asteroids Itokawa and Ryugu.

Those samples have provided insights into primitive solar system materials and the chemistry that may have contributed to the early Earth. A Phobos sample would extend that work into the Mars system.

NASA’s contribution to MMX is distinct from its separate Mars Sample Return planning, which focuses on samples collected by the Perseverance rover. The two efforts address different but complementary questions. Perseverance’s samples are selected from carefully documented rock outcrops on Mars. MMX material could offer a broader, potentially older, and more mixed record of Mars and its cosmic surroundings.

## What Is Known—and What Remains Uncertain

The broad mission goal is clear: MMX is intended to characterize Phobos and Deimos, investigate their origins, and return material from Phobos. NASA’s MEGANE instrument is a confirmed contribution to the JAXA-led effort.

However, the final scientific conclusions cannot be predicted in advance. Researchers do not yet know whether