Japan's Martian Moons eXploration (MMX) mission aims to probe and observe Mars' two moons, Phobos and Deimos, collect surface material, and return them to Earth.

MMX is scheduled to launch in 2024 and bring back rocks and other samples, possibly from Phobos, the larger of the two moons, five years later in 2029.

That puts Japan and its space agency JAXA in direct competition with the USA and Europe. The European Space Agency (ESA) and America's NASA are working on a joint mission to bring back samples from the planet, but that may be two years later in 2031.

Those samples would be collected by NASA's Perseverance rover, which is on its way there now. The rover will store samples in a process called "sample caching," and wait until they can be retrieved later. Those would be the first samples returned from Mars.

But JAXA says the Martian moons are a special case in themselves, and they can tell us about the whole Martian system.

A race for human space exploration

So, they are all in a race for science and technology — a friendly race, as it were — because such missions tend to be both challenging and collaborative. And they aim to benefit humanity in more ways than just the immediate objectives.

These missions are not just about bringing back rock and soil samples. They will also test the technology required to launch vehicles on and from Mars.

In July, NASA sent a helicopter called Ingenuity to Mars, strapped to the belly of its rover, Perseverance. The helicopter will be the first vehicle to test powered flight in the Martian atmosphere.

Mars' atmospheric density is less than 1% of Earth's and that can affect flight in a number of ways, especially during take-off and landing.

But launching to exit the planet will require far more than mere ingenuity — for a start, it will take a load of extra fuel, brought from Earth (or produced on the planet?) for any vehicle to get up and escape the Martian atmosphere, its gravity and orbit.

Human habitat on a Martian moon

All these tests will play into both commercial and non-commercial efforts to get humans to Mars and back again.

In an email to DW, scientists at JAXA explained why Japan considers the MMX mission an important part in its own preparation for human exploration "beyond [our] Moon and to the Martian system."

"Phobos is a possible location for a human base," wrote the anonymous scientists, "since launch is likely to be easier from the [Martian] moon's low gravitational environment than from Mars' surface. In addition, MMX is carrying a radiation detector to assess dangers to a future human crew."

So, what exactly­ is MMX and why the moons?

The MMX mission involves a spacecraft that will enter a Quasi Satellite Orbit around the Martian moon, Phobos, a lander with scientific instruments and tools, and a return vehicle. The German space agency DLR and the French space agency CNES are co-developing the lander or rover.  

Its primary objective will be to help scientists learn and understand more about the Martian moons and the planet — to "clarify" knowledge on their origin and evolution.

The creation of this system is one of the keys to solving the mysteries of planetary formation in the solar system, say the JAXA scientists.

"The Martian system sits at the gateway between the inner and outer solar system," they write in their email to DW. "Unlike Mars itself, which will have evolved through a multitude of geo-physio processes since its first formation, the moons preserve an earlier time in the history of the system."

There is some speculation that Phobos and Deimos may be a "captured asteroid," trapped in a Martian orbit.

"In that case, the moons [would] preserve a record of the material that was transported through the solar system towards the terrestrial planet region. This is particularly important from the standpoint of Earth's habitability, as the Earth is often considered to have formed dry and received water via icy meteorites scattered towards the planet from the outer solar system," say the scientists. "If the moons are captured, their composition will record what materials, including hydrated minerals and organics, would have arrived on the young Earth."

There is, however, evidence to contradict that theory. For instance, that the moons formed from debris ejected from Mars after it experienced a giant impact.

"That would make the two moons time capsules for early Mars, recording a period when Mars was thought to have more closely resembled the young Earth and potentially even be habitable," write the scientists. "A sample from this epoch would confirm this evolutionary picture from Mars, allowing us to understand how habitability develops and — indeed — ends."

JAXA is in talks with international scientists to determine the best location on Phobos for collecting the MMX samples.

Observation instruments

MMX will use a telescopic camera called TENGOO to observe the terrain of the moons, delivering images at a resolution of about 40 cm. Another camera will observe the moons' topography.

A near-infrared instrument called MacrOmega will observe the distribution of "hydrous minerals, water-related substances and organic matter" on the surface of the moons. That's being developed with CNES. 

And that's just three of the probe's six instruments.

Other objectives include the development of the technology required for return trips between the Earth and Mars and establishing "optimal communication technologies," using a newly developed, Deep Space Network ground station.

How MMX differs from other Mars missions

JAXA says results from the MMX mission will complement other missions that are focused on the Red Planet itself, such as Perseverance, the UAE's Hope orbiter, or China's Tianwen-1 orbiter and rover.

The scientists describe MMX as an investigation of the Martian system, rather than a detailed investigation on the planet.

"A sample from Phobos will contain grains from all over Mars' surface, rather than the in-depth study of a single location performed by the rovers," they say. "This will help distinguish what is typical for Mars and what may be confined to a single location and also how conditions may have changed over time."

Evolution in Japanese space exploration

Japan's original Mars exploration was the NOZOMI (PLANET-B) spacecraft, which launched in 1998. NOZOMI quickly ran into problems, took four years to reach the planet, and then failed to enter its orbit.

Since then, however, Japan has chalked up a few sample return mission successes, targeting small bodies, such as asteroids, comets and moons.Those successes started about a decade ago with Hayabusa, "the first spacecraft to return a sample" from an asteroid, Itokawa.

And now its successor, the asteroid explorer, Hayabusa-2, is returning to Earth with surface and sub-surface samples collected from a C-type asteroid called Ryugu.

The Martian moons are also C-type rocks, a class that is thought to contain both hydrated minerals and organics. All this together will hopefully "extend this map of the beginnings of habitability" in our solar system, write the scientists.

Sample return missions such as these are "always challenging," — even the first Hayabusa mission, which ended in success, ran into unexpected challenges along the way. But JAXA's scientists say "it is these challenges that push and improve technology that can be used in both scientific and human exploration, both in space and at home."