The Japanese Space Agency (JAXA) mission to the Martian Moon Phobos could be a good opportunity to seek signs of life on the red planet, team members believe. The mission aims to bring back a material sample to Earth by 2029, beating other space agencies' efforts to return samples from the Martian surface. Martian material accumulates on its moons – and, the logic goes, this could include indicators of past life.
Although each generation of Martian rovers carries more sophisticated testing equipment, they remain far behind Earth-based laboratories. Martian gravity presents an obstacle to return missions – but the moons Phobos and Demos are so tiny it will be simple for a lander to take off again, bringing samples with it.
In the journal Science, JAXA scientists Dr Ryuki Hyodo and Professor Tomohiro Usui explain the Martian moons should host dust kicked off the planet itself by asteroid impacts. If Mars hosts life – or ever did – its remnants should have found their way to the moons.
Material from Earth has been found on our own satellite, and Phobos is closer to Mars than the Moon is from Earth. “Throughout the history of Mars, numerous asteroidal impacts on Mars have produced martian impact ejecta, and a fraction of the ejected material has been delivered to its moons,” Hyodo and Usui write.
Indeed, lower Martian gravity means smaller impacts can launch material farther into space than on Earth, and some will eventually be collected by one of the passing moonlets.
Hyodo and Usui are part of a team that previously estimated at least 0.1 percent of Phobos' surface soil was originally Martian. Given Phobos' small size and low gravity, a spacecraft will be able to hop easily between locations to take multiple samples, unlike on Mars itself. Also, the diversity of impacts will mean samples will originate from many parts of Mars. Therefore, JAXA may find itself with a much more representative sample of Mars' diversity than the larger space agencies, which will each collect only from one small part of the planet's surface.
The Martian Moon eXploration (MMX) mission intends to launch in 2024 and return by 2029. A joint NASA/European Space Agency mission intends to bring the samples Perseverance is now collecting to Earth in approximately 2031, while a Chinese Martian sample return is planned for 2030.
Bits of Mars – in the form of meteorites knocked off the surface that eventually made their way to Earth – have already been the subject of advanced testing. Possible signs of life in one of these created a media storm in 1996. However, by the time these meteorites were discovered they had been on Earth for thousands of years, raising the risk of contamination.
With no atmospheres or water of their own, that won't happen on Phobos and Deimos. Nor is there a danger of bringing back still living Martian microorganisms from Phobos to create new plagues – radiation exposure on the moon's surface will have killed anything living long ago.
Hyodo and Usui call this optimum combination for research SHIGAI, which stands for Sterilized and Harshly Irradiated Genes and Ancient Imprints in English – also meaning “dead remains” in Japanese.
JAXA has other reasons to visit Phobos. Recent evidence has emerged that Phobos and Deimos were once part of a single larger moon, something a mission there could verify or refute.
