Japan just took a big swing at one of the oldest puzzles in the solar system. On Monday, October 19, the Japan Aerospace Exploration Agency (JAXA) launched its Martian Moons eXploration mission, better known as MMX, on a journey to Mars. If it works, MMX will be the first spacecraft ever to land on a Martian moon, collect a sample and bring it home to Earth.

Here’s what happened at launch, what the mission plans to do, and why a lumpy little moon called Phobos matters so much to planetary scientists.

A clean launch from Tanegashima

MMX lifted off on an H3 rocket from Pad 2 at the Yoshinobu Launch Complex at Tanegashima Space Center at 3:41 p.m. EDT, which was 4:41 a.m. local time on October 20 in Japan. According to Space.com, it was the 10th flight of the H3, the two-stage expendable rocket developed by JAXA and Mitsubishi Heavy Industries.

The flight went by the book. The rocket dropped its four solid boosters in pairs before the two-minute mark, shed its payload fairing shortly after, and the upper stage then fired a second time about an hour after liftoff for a trans-Mars injection burn of roughly six and a half minutes. MMX separated from the upper stage about 71 minutes after launch, setting off loud cheers in mission control on JAXA’s webcast.

The long road to Phobos

MMX is now flying under its own power. The cruise to Mars takes about 10 months, with arrival planned for August 2027. Once there, the spacecraft’s propulsion module will fire to put MMX into what’s called a quasi-satellite orbit around Phobos. In plain terms, MMX and Phobos will travel around Mars together, with the spacecraft looping close to the moon the whole time.

The plan from there is ambitious:

  • Study Phobos for about three years. Phobos is only about 14 miles (22 kilometers) wide, and MMX will map it in detail with its science instruments.
  • Drop off a rover. MMX carries IDEFIX, a small rover built jointly by the French and German space agencies, scheduled to roll onto Phobos in late 2028 or early 2029.
  • Land twice and collect samples. After choosing landing sites, MMX will touch down two separate times to collect material and stow it in its return capsule.
  • Visit Deimos. MMX will then shift into a longer orbit for a series of flybys of Deimos, Mars’ even smaller moon at about 8 miles (14 kilometers) across.
  • Come home. The spacecraft is set to leave Mars in November 2030, with the sample capsule landing in Australia in 2031.

Why scientists care about two tiny moons

Phobos and Deimos are odd. They aren’t round; both are oblong and lumpy, more like potatoes than proper moons. Scientists have argued for decades about where they came from, and there are two main theories.

One says they formed from debris after a giant impact knocked material off Mars, similar to the leading explanation for Earth’s moon. Their nearly circular orbits around Mars’ equator fit that idea. The other theory says they are asteroids from the early solar system that wandered too close and were captured by Mars’ gravity. Their shapes and what telescopes can tell us about their makeup point that way.

A physical sample could settle the question. Once the material is back on Earth, scientists will compare its chemistry and minerals with Martian rocks and asteroid material. That answer would tell us more about Mars’ past and about how the rocky inner planets formed.

An international effort

JAXA leads MMX, but it has plenty of partners. NASA supplied a gamma-ray and neutron spectrometer called MEGANE, built by the Johns Hopkins Applied Physics Laboratory, along with a pneumatic sampler from Honeybee Robotics and communications support through its Deep Space Network. Space.com reports that NASA has invested about $87 million through the end of the mission, and in return at least 15% of the planned 10-gram (0.35-ounce) Phobos sample will be set aside for NASA researchers at Johnson Space Center in Houston. The European Space Agency is also a partner.

It’s worth remembering that this has been tried before. Russia’s Phobos-Grunt mission launched in November 2011 but never left Earth orbit because of a rocket problem, and it fell back over the Pacific Ocean in January 2012. SpaceNews describes MMX as the first mission that will attempt to return samples from a moon of Mars, and Japan brings real experience: its Hayabusa and Hayabusa2 missions already returned asteroid samples to Earth.

The bottom line

MMX’s launch is only the first step in a roughly five-year round trip, and the hardest parts, landing on a tiny moon with almost no gravity and getting the sample home, are still ahead. But the mission is off to a clean start. If it succeeds, a few grams of Phobos dust arriving in the Australian outback in 2031 could finally tell us how Mars got its moons. Until then, keep an eye out for MMX’s arrival at the Red Planet in August 2027.

Image: Phobos and Deimos by Giuseppe Donatiello via Wikimedia Commons, CC0 1.0