Japan’s Martian Moons Mission Gets Go Ahead

Artist impression of the MMX spacecraft. (Credit: JAXA)

Martian Moons EXploration (MMX) mission to explore moons, return soil sample from Phobos.

TOKYO (JAXA Program Update) — This week (19 February 2020), the MMX mission transitioned to become a JAXA Project: an official step in mission development authorised by the Japanese government. The mission was previously in the Pre-Project phase, where the focus was on research and analysis, such as simulating landings to improve spacecraft design. The focus will now move onto the development of mission hardware and software.

Project Manager Yasuhiro Kawakatsu gave a presentation to Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) outlining the assessment performed for the mission’s transition. The slides in Japanese are available here and the contents is summarised below.

In order to transition from a JAXA Pre-Project to Project, the MMX mission team had to consider factors such as the importance of the scientific goals, the success criteria, the implementation system, the financial plan, schedule and identify risks and countermeasures.

The Martian Moon eXploration (MMX) spacecraft has a planned launch date in JFY 2024 (Japan financial year) and will visit the two moons of Mars, Phobos and Deimos. Phobos has been selected for surface operations, with the spacecraft landing for several hours to collect a sample of at least 10g using a corer that can gather material from a minimum of 2cm below the moon’s surface.

The spacecraft will then leave the Martian system and return the sample to Earth, completing the first round-trip to the Martian system.

ISAS is focused on exploring the smallest bodies in our Solar System. (Credit: JAXA)

Mars: the Gatekeeper

Mars is a focal point for the international science community due to its importance as a possible habitable planet. While Mars’s surface is not currently able to support life, the planet is thought to have had a more Earth-like environment in the past, including the presence of surface oceans.

Water may even now still exist beneath the planet’s surface. But to understand Mars’s evolution and the development of the Earth’s own habitability, we need to know how Mars acquired its water. This is a central question for JAXA’s small body missions.

The terrestrial planets in our Solar System are thought to orbit too close to the Sun to have retained volatiles during formation. Instead, water and organics are speculated to have been delivered via comets and asteroids that formed in the colder regions of the outer Solar System.

The distance where water can freeze into ice is known as the snow line (or ice line); a transition point that sits just beyond the orbit of Mars. Mars therefore sits at the gateway of water arrival in the inner Solar System and evidence of its delivery may be imprinted on the Martian system.

One such imprint may lie in the composition of the moons. The formation of the two Martian satellites is strongly debated. With diameters of 23km and 12km respectively, Phobos and Deimos resemble asteroids and may have been captured by Mars’s gravity as they were scattered inwards from the asteroid belt.

If so, the pair would be a capsules for water transport through the Mars gateway to the terrestrial planets. Alternatively, the moons may have formed during a giant impact with Mars. This would make the moons capsules of shards of the early Martian environment, revealing how water came and went on the red planet.

A main mission goal for MMX is to decipher the origin of the moons by remote examination and returning a sample for compositional analysis. Both possible origins will provide clues as to how water is delivered to inner planets.

Artist concept of the early Martian environment (left) – believed to contain liquid water and a thicker atmosphere – versus the cold, dry environment seen at Mars today (right). (Credit: NASA GSFC)

Towards Human Exploration

The MMX mission is the next step in small body exploration and sample return at JAXA, which began with Hayabusa’s journey to asteroid Itokawa. This was followed by the Hayabusa2 mission, which is currently returning to Earth carrying a sample of material from asteroid Ryugu.

The technology in these missions will be further developed for MMX, which must return a sample from a small body orbiting within the deep gravitational well of a planet.

The use of a corer to collect a sample exceeding 10g is also very different from the Hayabusa2 mission, which touched the asteroid surface only briefly to gather a minimal sample of 0.1g. These technological advances will benefit future missions, including those aimed at sending a human crew to the red planet.

Phobos and Deimos have been considered as a possible human base in the Martian system. The MMX spacecraft will test and demonstrate the necessary technology for entering and leaving Mars’s gravitational well, landing and navigating on the surface of low-gravity bodies and deploying equipment for tasks such as surface sampling. The mission will also measure the radiation environment, which is a concern for humans travelling beyond the Earth’s protective magnetosphere.

“Humans can realistically explore the surfaces of only a few objects and Phobos and Deimos are on that list,” noted NASA Chief Scientist, Jim Green. “Their position orbiting about Mars may make them a prime target for humans to visit first before reaching the surface of the Red Planet, but that will only be possible after the results of the MMX mission have been completed.”

MMX mission overview. The planned launch for the spacecraft is in JFY 2024. (Credit: JAXA)

Choosing Phobos

Phobos was deemed to be the more scientifically desirable moon for sample collection. More data currently exists for this larger moon, helping to narrow down the best location for surface sampling. Phobos also has regions suggestive of two different compositions, while Deimos has only one. This implies more information might be available from a Phobos sample than from his sibling.

Additionally, the closer orbit to Mars means that ejecta from the Martian surface is expected to be more numerous on Phobos than on Deimos, allowing an additional source of information about Mars’s evolution.

Reaching the inner moon requires more propellent than for the outer Deimos, but the extra weight has been approved in the spacecraft design. One concern for all planetary space missions is the risk of contamination, for which JAXA complies with the Planetary Protection Policy (PPP) laid down by COSPAR.

 Simulations performed by researchers at JAXA showed a negligible chance of organisms being collected by the MMX spacecraft, allowing the mission to have the same planetary protection policy as Hayabusa2.

The challenges with landing on Phobos were researched during the pre-project in a phase known as front loading, which is research and development specifically designed to demonstrate important technologies in order to reduce uncertainty and risk. During front loading, repeated simulations of landing on the surface of Phobos revealed that thicker legs with a wider spacing would increase the spacecraft stability.

An International Collaboration

The MMX spacecraft is equipped with eleven instruments, four of which will be provided by international partners at NASA (USA), ESA (Europe), CNES (France) and DLR (Germany).

The JAXA-built instruments include the telescopic (narrow-angle) camera, TENGOO, for observing detailed terrain, the wide-angle camera, OROCHI, for identifying hydrated minerals and organic matter, the LIDAR laser altimeter, the Circum-Martian Dust Monitor, CMDM, the Mass Spectrum Analyser, MSA, to study the charged ions around the moons, SMP sampling device and sample return capsule, and the radiation environment monitor, IREM.

NASA will contribute the gamma ray and neutron spectrometer, MEGANE, to examine the elements that constitute the Martian moons, and also the P-sampler; a pneumatic sampling device. CNES are building MacrOmega, a near-infrared spectrometer that can identify mineral composition, and working with DLR to design a rover to explore the moon surface. ESA will additionally assist with deep space communication equipment.

The MMX mission is therefore an international collaboration to investigate one of the most important unexplored areas of the Solar System for understanding both how a habitable planet is born and how humans might explore beyond our own world.