Japan is preparing to launch a spacecraft to Phobos, one of Mars's two small, potato-shaped moons. It will be the world's first mission to return samples from a Martian moon. The launch is planned on Japan's new H-3 rocket.
The MMX (Martian Moons eXploration) project is being carried out by the Japan Aerospace Exploration Agency (JAXA). The international team includes NASA and other agencies that are providing equipment and communications. Scientists hope the samples will help explain how Phobos and its smaller brother Deimos formed and will shed light on the origin of life in the Solar System.
Mars's moons remain a mystery. Phobos and Deimos are named after the Greek gods of fear and dread, the sons of Ares, whose Roman counterpart is Mars. Several Russian attempts to land on Phobos, including a 2011 mission, ended in failure.
The main question is how these uneven, crater-covered bodies formed and what they are made of. Some scientists believe they are debris left after a large celestial body collided with Mars. Others believe the moons are asteroids that arrived from other regions of the Solar System. "We can almost certainly come to a conclusion by analyzing samples of Phobos soil," mission project scientist Kiyoshi Kuramoto said.
Phobos, about 20-30 km in diameter, orbits Mars at a distance of roughly 6,000 km and makes three revolutions per day. It was chosen for sample collection because it is closer to Mars than Deimos and may contain more information about the planet. JAXA estimates that material from Mars will make up about 0.1% of the collected soil. The samples will also help explain the origin of Deimos, since both moons are believed to share common roots.
The journey to the Red Planet is long: the minimum distance between Earth and Mars is 55 million km, but the actual flight trajectory will be 500-600 million km. After launch, the spacecraft will reach the vicinity of Mars around August 2027. It will then spend three years flying around Phobos, collecting data and samples, and will return home in 2031.
MMX consists of three modules - propulsion, exploration and return - and weighs about 5 tonnes. Only the third module will return home, with a capsule that will hold the samples. On board are 13 instruments, including the French-German Idefix rover, which will be the first to land on Phobos. During its 100-day mission around 2029, it will study the surface to help with the subsequent soil collection. After landing, MMX, Japanese scientists plan to collect at least 10 grams of soil in two attempts, using American and Japanese methods. A NASA device will use compressed gas to lift dust from the surface into a container, while a Japanese drill will take samples from a depth of about 2 cm.
The collected samples will be placed in a heat-shielded capsule capable of surviving entry into Earth's atmosphere. It is expected to land in Australia and then be delivered to Japan. Japan has previously returned asteroid samples on the Hayabusa missions, in 2010 and 2020.
The main difficulty is Phobos's extremely low gravity: it is only one two-thousandth of Earth's. To avoid bouncing on contact, the exploration module is equipped with a four-legged landing gear with shock absorbers. The rover has wheels capable of gripping the soil in such conditions, can turn over and move "at a snail's pace," JAXA says. No more than two hours are allotted for landing and sample collection.