JAXA, the Japanese Aerospace Exploration Agency, is carving out a niche for itself in sample-return missions. Their Hayabusa mission was the first mission to sample an asteroid when it brought dust from the asteroid Itokawa to Earth in 2010. Then its successor, Hayabusa 2, brought back a sample from asteroid Ryugu in 2020.
Now JAXA has the Martian moon Phobos in its sights and will send a spacecraft to sample it as soon as 2024. The mission is called Martian Moons eXploration (MMX), and it’ll use a pneumatic vacuum device to collect its samples.
Why go to Phobos and sample it? Because it’s an unusual moon and understanding it better could answer questions about it and our Solar System. And we always want more answers.
Phobos is the larger of Mars’ two moons, the other being Deimos. Both moons are irregularly shaped and look kind of like potatoes, especially Phobos. Phobos has a mean radius of only 11 km (7 mi). It’s closer to Mars than Deimos and orbits only 6,000 km (3,700 mi) from the planet’s surface. It moves rapidly, taking only 7 hours and 39 minutes to complete one orbit and completes three orbits each day.
Much of Phobos’ surface is covered with strange linear grooves. New research bolsters the idea that those iconic grooves were carved by boulders blasted free from Stickney crater (the large depression on the right). Image Credit: NASA/JPL-Caltech/University of Arizona
Phobos is probably a captured rubble-pile asteroid, although astronomers still debate its nature. It has a lot in common with carbonaceous asteroids and is one of the least reflective objects in the Solar System.
The tiny moon is getting closer and closer to Mars. Every year it gets about 2 cm closer and will eventually be destroyed. In about 30 million to 50 million years, it will either smash into the surface of Mars and be utterly destroyed or be torn apart by tidal forces and form a debris ring around the planet. In fact, one hypothesis says that Mars’ moons were formed from dust created by a giant impact on Mars. Dust to dust, as they say.
An illustration of Mars with a debris ring. Image Credit: SETI
Japan leads the MMX mission, but NASA, the CNES (France), and the DLR (Germany) are also contributing. It has two broad goals: (1) determining the origin of the Martian moons and (2) observing processes in the circumplanetary environment of Mars, based on remote sensing, in situ observations, and laboratory analyses of returned samples of Phobos regolith. Scientists think that a better understanding of the Mars-Phobos-Deimos system will shed light on the planetary formation process in the Solar System.
Getting a sample from Phobos faces several obstacles. The moon is not massive enough for a spacecraft to enter orbit around it in the usual way. Instead, MMX will enter orbit around Mars and then perform quasi-satellite orbits. Those orbits become unstable over time but should allow for several months of operation near Phobos. This maneuver also enables the MMX lander to reach Phobos’ surface.
JAXA designed the MMX mission with three components: a propulsion module, an exploration module, and the return module. The French CNES space agency suggested that the mission should also deploy a tiny rover
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