The Japan Aerospace Exploration Agency (JAXA) is planning to launch a spacecraft on Tuesday that will journey to Phobos and back in about five years, collecting the first-ever rock and soil samples from a moon of Mars.

According to Kawakatsu Yasuhiro, project manager for the Martian Moons Exploration Mission (MMX), the Phobos mission will provide valuable information about the formation of the solar system, offer a glimpse into the origins of life, and possibly pave the way for using Phobos as a base for a manned mission to the surface of Mars.

“Despite their potential importance, Martian moons have never been fully investigated. They are known as the most important unclimbed mountains in the solar system,” he said.

Phobos is the larger of the Martian moons, the other being named Deimos. Both of these moons are tiny compared to Earth’s Moon, and they orbit the planet more closely and at higher speeds. Phobos is only 17 miles across at its widest point, and it completes its orbit around Mars three times a day. Almost half of its surface is covered by a single immense crater, known as Stickney Crater, created long ago by a meteoric impact that nearly shattered the moon.

These qualities make landing on Phobos a formidable task. The Russians made four attempts to send probes to Phobos between 1988 and 2011. Only one of them, Phobos-2, made it to Martian orbit, suffering a catastrophic computer failure when it was heartbreakingly close to touching down on the moon in March 1989.

The MMX mission is an international endeavor led by the Japanese space agency, with support from NASA, which will supply an instrument called the Mars-moon Exploration with Gamma Ray and Neutrons (MEGANE) detector. This device, developed by the Johns Hopkins Applied Physics Laboratory (APL) and Lawrence Livermore National Laboratory, could help to answer the vexing question of where Phobos and Deimos came from.

Ever since the moons of Mars were first observed in 1877, astronomers have wondered if they were birthed from the mass of Mars itself, or if they were wandering asteroids captured by the gravitational pull of the planet.

“What are these little space potatoes? We can’t explain Phobos or Deimos right now. They shouldn’t exist, but they do. They’re super weird, they’re super small and they’re super puzzling,” Dr. Abigail Fraeman of NASA’s Jet Propulsion Laboratory (JPL) told CNN on Monday.

Fraeman noted that the spacecraft and rovers mankind has sent to Mars have collected quite a bit of information about Phobos and Deimos, but none of that data fits any hypothesis for the origin of the two moons perfectly.

The MEGANE system could help to finally solve the mystery by measuring neutron and gamma ray energy from the surface of Phobos, creating an elemental analysis that might conclusively determine if the moons are made of the same material as Mars itself — almost like performing a DNA test to determine the ancestry of a human being.

“If you had a giant impact, what happens is the materials get very hot, and you will cook off these volatile elements. In contrast, a lot of asteroids that we see have higher abundances of these volatile elements,” explained planetary scientist David Lawrence of APL.

The MMX spacecraft will first deposit a tiny rover called Idefix on the surface of Phobos. Idefix was developed by the German Aerospace Center and the National Center for Space Studies in France.

The toy-sized Idefix rover will help to determine an optimum landing point for the larger, but still very small, lander carried by the MMX spacecraft. The gravity of Phobos is so weak that the mission plans to drop the lander from less than 350 feet up and let it bounce gently off the surface.

The lander is about the size of a case of beer, while the Idefix rover looks like a toy. The plan is to make two drops on the opposite sides of Phobos, because its dark side appears to have a very different composition from the light side. The lander contains an American-made system that collects surface dust using pressurized gas, plus a Japanese system that can dig about an inch into the surface of the moon to harvest samples.

Collecting samples from multiple locations on Phobos could help to answer some lingering questions about the origins of life in the solar system, and the ever-intriguing question of whether there was ever any sort of life on the surface of Mars. If Phobos is a chunk of Mars blown into orbit by some ancient cataclysm, it could contain a chemical snapshot of what Mars looked like millions of years ago. If the little moon is a captive asteroid, it might contain chemicals from the far reaches of the solar system.

MMX will take a year to reach Mars, orbit Phobos for about three years, make a close flyby of Deimos, and then take another year to bring its historic rock samples home, with a splashdown of the heat-shielded sample capsule planned off the coast of Australia in 2031. The total amount of material the lander aims to bring back from Phobos will weigh less than half an ounce.

The MMX mission aims to reach Phobos and return before China’s Tianwen-3 sampling mission reaches the surface of Mars and returns to Earth, sometime later in 2031.