Japan's space agency is scheduled to launch its Martian Moons Exploration (MMX) mission on 20 October, aiming to collect material from Mars' moon Phobos and return it to Earth in 2031.
The spacecraft is scheduled to lift off from the Tanegashima Space Center in Japan at 4:41 am local time on 20 October, or 8:41 pm British Summer Time on 19 October, says the BBC.
If successful, the mission would mark the first time material has been retrieved from the Martian system and returned to Earth for laboratory analysis.
The spacecraft is expected to reach the Martian system in August 2027. It will study Mars' two moons, Deimos and Phobos, before collecting samples from Phobos. The return capsule is scheduled to land in South Australia's Woomera desert in 2031.
"There hasn't yet been a successful mission to go to Phobos and bring a bit back to Earth. I think this is an incredibly ambitious and fun mission," said Prof Sara Russell of the Natural History Museum, deputy for MMX sample analysis.
Exploring Mars' two moons
Mars has two small, irregularly shaped moons, Phobos and Deimos, which are about 20 km and 10 km across, respectively. Both have been described as looking "a bit like space potatoes".
The MMX spacecraft will study Deimos before shifting its focus to Phobos, where it plans to deploy a small exploration rover to assess the terrain and identify a suitable landing location.
Landing on Phobos presents technical challenges because of the moon's weak gravity and the gravitational influence of Mars.
"The moon itself doesn't have very much of its own gravity... But it's next to an enormous planet that's got a much higher gravity, and that makes it much harder to get a rover onto the surface," Russell said.
After the rover assesses the surface, the main spacecraft will land on Phobos and use a robotic arm and two samplers to collect moon dust.
Scientists aim to collect 10 grams of material
The mission aims to collect approximately 10 grams of material from Phobos for return to Earth. Researchers say even this small quantity could support detailed scientific analysis.
"It's a very small [amount] actually... However we can do several studies even on individual grains… You don't need to have kilos back from a surface in order to do science. So it's worth every gram," said Dr Chrysa Avdellidou of Leicester University.
Scientists already possess Martian meteorites that reached Earth naturally, but those rocks can be contaminated by Earth's air, soil, dust and water after landing.
Collecting material directly from Phobos would provide a sample that has not been exposed to Earth's environment in the same way.
Mission seeks to explain the moons' origins
Scientists remain uncertain about how Phobos and Deimos formed approximately 4.5 billion years ago. The MMX mission aims to investigate two competing theories.
One proposes that a large object struck early Mars, ejecting debris that eventually formed the two moons. The other suggests they are asteroids that were captured by Mars' gravity.
Analysing the samples' chemistry and mineral composition could help scientists determine which explanation is more likely.
"When we get the sample back, we'll be able to look in detail at its chemistry and its mineral composition - and the two hypotheses will produce very distinct results... It should be pretty much immediately obvious.. whether it's the product of this dramatic impact or whether it's a captured asteroid. So we'll find that out really quickly," Russell said.
The samples could also contain material originating directly from Mars. Because Phobos orbits close to the planet, meteorite impacts on Mars can eject fragments into space that subsequently reach the moon.
"One of the really exciting things is that Phobos is so close to the Mars surface that whenever there's an impact into the Mars surface, little grains might actually become implanted into Phobos itself... And that means that the sample we get back may actually contain grains of Mars as well. So it can give us really direct information about the composition and history of Mars," Russell said.
International competition to return Martian samples
Returning material from the Martian system has been a major goal of space exploration. NASA's Perseverance rover has been collecting and storing surface samples in canisters on Mars since 2021.
However, the joint NASA and European Space Agency Mars Sample Return mission was effectively cancelled after funding was halted by the US Congress.
China is planning its own Mars sample return mission, scheduled to launch in 2028 and return to Earth in 2031.
If successful, Japan's MMX mission could become the first to return samples from the Martian system, providing researchers with material to investigate the origins of Mars' moons and potentially gain further insight into the planet itself.