Japan launches mission to bring home a piece of the Martian moon Phobos

The climax for MMX will come in 2029, when the spacecraft will attempt up to two landings on Phobos.

Japan launched a $578 million mission Monday on a five-year expedition to land on the largest moon of Mars and retrieve samples for return to Earth, a daring international project that could yield new insights into the formation of the Solar System.

The robotic Martian Moons eXploration mission, known as MMX, lifted off at 3:41 pm EDT Monday (4:41 am Japan Standard Time Tuesday) from Tanegashima Space Center in southern Japan.

The MMX spacecraft rode into orbit atop a 207-foot-tall (63-meter) H3 rocket, Japan’s flagship launch vehicle. The rocket assigned to MMX debuted a new souped-up configuration with four strap-on solid rocket boosters, full-throttle main engines, and an extended payload shroud to accommodate the demands of Japan’s heaviest and most ambitious interplanetary mission to date.

The rocket’s upper stage accelerated the MMX spacecraft to a top speed of more than 24,000 mph, fast enough to break free of Earth’s gravitational pull for the 10-month voyage to Mars. The nearly 9,900-pound (4.5-metric ton) spacecraft—two-thirds of its mass comprised of propellant—separated from the H3 rocket about 71 minutes after liftoff.

Hiroshi Yamakawa, president of the Japan Aerospace Exploration Agency (JAXA), declared the launch a success. “A long journey of five years has just started,” Yamakawa said.

MMX established contact with ground controllers, unfurled its solar panels, and was in a “very stable condition” soon after separating from the H3 rocket, according to Yasuhiro Kawakatsu, the mission’s project manager at JAXA. “So far, so good.”

“The MMX [mission] we launched today is a challenging mission aiming for the world’s first sample return from the Martian moons,” said Yoshihiro Seki, Japan’s science minister. “We hope that the results obtained through this mission will contribute to the development of our nation’s space science and exploration technology.”

Building on a legacy

The mission to the Martian moons builds on Japan’s success in leading the Hayabusa and Hayabusa 2 missions, the world’s first two spacecraft to bring back pristine specimens from asteroids. Scientists believe Phobos could itself be an asteroid that was captured into orbit around Mars billions of years ago. One of MMX’s science goals is finding out if that theory is correct.

With the Hayabusa missions, sample returns from deep space have become a “speciality” for Japan’s space program, Kawakatsu said. For MMX, Japan attracted contributions from NASA and space agencies in Europe.

“We have a proven track record of success in these areas,” Kawakatsu said. “Because of this, I believe they are participating with the understanding that if they want to conduct celestial body sample returns, joining a mission led by Japan is more certain to succeed than the US or Europe launching their own missions.”

MMX will spend about three years in the vicinity of Mars after arriving there next August, conducting a series of encounters with the Martian moons Phobos and Deimos. Phobos is the larger of the two, with a lumpy, potato-like shape, an average diameter of 14 miles (22 kilometers), and a surface area comparable to the city of Houston.

Upon reaching Mars, MMX will jettison its propulsion module, dead weight after burning all its fuel to enter orbit around the red planet. That will leave the main section of the MMX spacecraft and its four-legged landing gear, known as the exploration module, to move closer to Phobos.

The moon’s gravity is too weak and the pull of Martian gravity too strong for the MMX spacecraft to enter into a stable orbit around Phobos. Instead, the spacecraft will fly in a so-called quasi-satellite orbit, remaining bound to Mars while still able to maneuver around Phobos.

The mission’s reconnaissance of Phobos will culminate in late 2028 or early 2029, when the MMX mothership will release a small rover to drop onto Phobos. The four-wheeled robot, named Idefix, is a contribution from the French and German space agencies. Idefix, the size of a large shoebox, will attempt to drive around Phobos for up to 100 days while grappling with the moon’s rough topography and tenuous gravity, less than one-thousandth that of Earth’s.

The climax for MMX will come later in 2029, when the main spacecraft will attempt up to two landings on Phobos. The probe’s landing gear is designed to absorb energy of each landing to mitigate the risk of tipping over or bouncing back into space, a real concern with the feeble and uneven gravity field on Phobos.

The spacecraft will stay on the surface of Phobos for several hours, using two independent mechanisms to capture samples from the Martian moon. A coring drill on the end of the probe’s robotic arm will scoop out a cigar-shaped specimen, while a NASA-provided pneumatic sampler on one of the craft’s landing legs will fire a cartridge of high-pressure nitrogen gas to sweep bits of Phobos in a collection canister.

How did they get there?

All told, scientists expect MMX to retrieve at least 10 grams, or one-third of an ounce, of material from Phobos. After climbing back into space, MMX will discard its landing gear and fire its engines in 2030 to head for Earth, where it will guide a sample return capsule toward a remote landing zone in South Australia in 2031.

Scientists will recover the samples for analysis in laboratories in Japan. US researchers will get 15 percent of the Phobos specimens in return for NASA’s contributions to the MMX mission, which include one of the spacecraft’s samplers and a gamma-ray and neutron spectrometer to measure the elemental makeup of the Martian moons.

“One of the most intriguing questions about Phobos and Deimos is simply why these two little moons are there in the first place,” said Tom Statler, lead scientist for solar system small bodies at NASA. “In some ways, they resemble asteroids from the outer part of the asteroid belt, so they could be asteroids that were captured by Mars’s gravity. But there are other lines of evidence pointing to these moons being remnants of a giant impact early in Mars’s history.”

“By going to the Martian moons, studying them up close, and bringing samples back to Earth, we’ll be able to determine whether Phobos material is more consistent with an asteroid composition or with debris created by a collision involving Mars,” Statler said.

Phobos is roughly 40 times closer to Mars than our Moon is to Earth. Its proximity to Mars means there is a chance MMX might scoop up traces of the red planet itself that rained down on Phobos after its formation or capture. This could offer a taste of what’s to come when scientists finally get their hands on specimens directly from the surface of Mars, a significantly more difficult undertaking than a sample return from Phobos.

The reconnaissance of Phobos by MMX could also help future mission planners consider whether the moon is a suitable location for human exploration, perhaps as a stopover between Earth and Mars, Kawakatsu said.

MMX is not the first mission to attempt a sample return from Phobos. Russia’s Phobos-Grunt sample return mission failed soon after launch in 2011, before it could set off for Mars. The Soviet Union launched two spacecraft to Mars equipped with Phobos landers in 1988, but ground teams lost contact with both spacecraft before they completed their missions.

With MMX, scientists hope to finally acquire the ground truth on the Martian moons they have sought for decades.

“Basically, these objects look more like primitive asteroids than anything else, but the data is coming from remote sensing from far away,” said Patrick Michel, a French asteroid scientist and co-leader of the Idefix rover project. “That cannot really tell us exactly what are the properties, as we can do with a sample return in the lab.”

“The goal of the mission is effectively to reveal the origin of the Martian moons,” Michel said. “If we understand the origin, that will tell us something about the early phases of the Solar System.”