Japan to send a spacecraft weighing about 4.2 tons for 10 grams of soil from Mars' moon: could they reveal the mystery of Phobos?
For just 10 grams of soil, Japan will send a spacecraft weighing about 4.2 tons to a Martian moon. The journey will take five years, and its outcome could help scientists solve one of the mysteries of the Solar System: where Phobos came from—whether it was a captured asteroid or formed after a giant impact with Mars.
The launch of Japan's Martian Moons eXploration (MMX) mission is scheduled for Monday, October 19, at 22:41 Kyiv time. If the expedition is successful, humanity will for the first time receive soil samples from the Mars system, specifically collected by a spacecraft. But to do so, it must perform two landings on Phobos, where gravity is so weak that a 25-kilogram rover will weigh as little as a 15-gram object on Earth.
The Japan Aerospace Exploration Agency JAXA confirmed the launch time on October 18. The H3 rocket is scheduled to lift off from Tanegashima Space Center on October 20 at 04:41 Japan time. A backup launch window is set from October 21 to November 9.
How 10 grams could reveal a billions-year-old mystery
Mars has two small moons—Phobos and Deimos. Despite decades of research on the Red Planet, scientists have not reached a unified conclusion about their origin.
According to one hypothesis, both moons were once asteroids captured by Mars' gravity billions of years ago. Another version suggests they formed from debris ejected into space after a collision between the young planet and a large celestial body.
To distinguish between these scenarios, researchers need to determine the precise chemical and mineralogical composition of Phobos' material.
This is where a small amount of soil can be more valuable than many remote observations. In Earth laboratories, specialists will be able to examine individual particles using high-precision instruments that are too large, complex, or sensitive to send into space.
Analysis of minerals, chemical elements, and isotopic composition will help test how similar Phobos' material is to Martian rocks or asteroid material.
According to scientists from the European Space Agency ESA, even tiny samples can contain information that cannot be obtained with instruments on board a spacecraft.
However, successful delivery of soil does not guarantee a final resolution of the debate: the results will have to be compared with existing models of satellite formation.
Phobos may contain particles from ancient Mars
There is another reason why researchers are particularly interested in this moon.
Over billions of years, Mars has repeatedly been hit by asteroids. Some collisions were so powerful that they ejected particles of Martian rocks far beyond the planet's atmosphere.
Some of this material could have settled on Phobos. Therefore, the collected soil could theoretically contain particles that preserved information about the ancient surface of Mars.
Such findings would supplement knowledge about the history of water, geological processes, and conditions that existed on the Red Planet billions of years ago.
This does not involve a direct search for living organisms. The main scientific goal of MMX is to investigate the origin of the moons and the evolution of the Martian system.
The most challenging part of the mission—landing on a tiny moon
Unlike the Moon or Mars, Phobos has extremely weak gravity. This creates unusual technical challenges: even a relatively small force can lift the spacecraft off the surface.
Before the main MMX probe lands, it will deliver the small Idefix rover to Phobos, developed by the French space agency CNES and the German Aerospace Center DLR.
Its mass is 25 kilograms, but the gravity on Phobos will act on it roughly like on a 15-gram object on Earth.
The rover will study surface properties and help specialists prepare for subsequent landings of the main spacecraft.
According to JAXA's plan, MMX is to perform two soft landings to collect samples. The duration of stay on the surface will be approximately two to three hours.
Two different devices are planned for obtaining soil. The first will be able to extract material from a depth of about two centimeters. The second uses a jet of compressed gas to lift surface particles and direct them into a special container.
This approach increases the chances of collecting the required amount of material on a virtually unstudied surface.
Five years of flight for a return to Earth
After launch, MMX faces nearly a year of interplanetary travel. According to ESA's schedule, the spacecraft should enter Mars orbit in August 2027, and in September begin close-range studies of Phobos.
In early 2029, the Idefix rover is planned to be delivered to the moon. The main sample collection operations are scheduled for 2030.
After that, the return module will head to Earth, conducting observations of Mars' second moon, Deimos, along the way.
In 2031, the capsule with samples is to enter Earth's atmosphere and land in Australia. It will then be transported to a specialized JAXA laboratory in Japan, where the collected material will be studied and prepared for international research groups.
Japan already has experience with such expeditions: the Hayabusa and Hayabusa2 spacecraft successfully delivered asteroid samples to Earth. However, a flight to the Mars system and back will be a significantly more challenging task.
Success of MMX will not only provide unique material for research but also test technologies needed for future missions returning samples from other celestial bodies.
Although the main goal of the five-year journey is just a few grams of soil, scientists expect to study them for decades—including with laboratory technologies that do not yet exist today.
Based on materials from: JAXA—launch date and time confirmation, JAXA—MMX science program, ESA—mission technical specifications, ESA—expedition program and timeline, NASA—MMX science objectives