Japan launched an ambitious $350 million mission to Mars on Monday, aiming to examine the Red Planet’s two moons in unprecedented detail. The spacecraft will deploy a small rover to Phobos, the larger moon, before landing itself to collect soil samples that will eventually be brought back to Earth.
The central objective of the Martian Moons Exploration mission, known as MMX, is to resolve how Phobos and the smaller Deimos formed. Scientists want to determine whether the moons are remnants of a massive impact early in the solar system’s history or asteroids that were captured by Mars’ gravity after passing nearby.
JAXA
Mars’ moons are tiny compared with Earth’s. Phobos is only about 17 miles wide at its broadest point, while Deimos measures less than half that size. Both have irregular shapes and an asteroid-like appearance, but their dimensions and form alone cannot reveal their true origins.
“One of the most intriguing questions about Phobos and Deimos is simply why these two little moons are there in the first place,” said Thomas Statler, who helped oversee the development of two NASA instruments carried by the MMX spacecraft.
“In some ways, they resemble asteroids from the outer part of the asteroid belt … but there (are) other lines of evidence pointing to these moons being remnants of a giant impact early in Mars’ history.”
Jaxa
The samples, scheduled to return to Earth in 2031, are expected to provide the evidence needed to settle the debate.
“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.
The mission began at 3:41 p.m. EDT, or 4:41 a.m. Japan time, with the dramatic launch of a Japanese H3 rocket from the Tanegashima Space Center. The facility is operated by the Japan Aerospace Exploration Agency, or JAXA.
Four solid-fuel strap-on boosters and two hydrogen-powered first-stage engines propelled the rocket through the dense lower atmosphere. The H3’s second stage then took over, carrying the spacecraft toward orbit.
NASA
The 9,900-pound MMX probe separated from the rocket 1 hour and 11 minutes after liftoff, following two burns by the upper-stage engine, and began its journey through space on its own.
If the mission remains on schedule, MMX will enter orbit around Mars in September 2027. Its flight path will allow it to travel around the planet in step with Phobos.
The spacecraft will spend three years in orbit, using a suite of instruments to study Phobos and the environment around it. Researchers will analyze the moon’s chemical and mineral makeup, assess whether it could serve as a staging point for future astronauts and deploy a small rover built by the German and French space agencies in early 2029.
The 55-pound rover has no braking rockets or other equipment designed to slow its fall. Because Phobos’ gravity is only one-thousandth as strong as Earth’s, the rover is expected to bounce across the surface before gently tumbling to a stop.
The rover is built to right itself regardless of how it lands and then begin exploring the moon’s surface. Its equipment includes navigation cameras, imaging systems to examine the soil as it moves, a laser instrument to identify minerals beneath the surface and a sensor to track soil temperatures.
JAXA
About a year after the rover arrives, around 2030, the MMX spacecraft will make one—and possibly two—touchdowns on Phobos to gather soil. The samples will be collected with two devices, one developed by JAXA and the other provided by NASA.
The mission’s formal requirement is to retrieve at least 10 grams of material, or less than half an ounce. The final amount could be greater, depending on the composition and texture of the surface soil.
MMX will then lift off, complete additional observations of Deimos and begin its return journey to Earth. The Phobos samples will be sealed inside an aerodynamic, heat-resistant capsule that will re-enter the atmosphere above Australia, where a recovery team will be waiting.
An international group of researchers will analyze the material once it reaches Earth.
“There’s a lot of adrenaline, a lot of excitement, and a lot of wow,” Statler said. “MMX will be the first spacecraft ever to return to Earth from the Mars system. That says a lot.”
Still, Statler said, “the most exciting thing of all” will be watching the sample-return capsule plunge through Earth’s atmosphere, opening it and seeing the Phobos material for the first time. “There is absolutely no lack of excitement and adrenaline on this mission.”