Japan’s Mission to the Martian Moons Will Return a Sample From Phobos. What Makes This Moon So Exciting?25 Feb 2020, 17:54 UTC
Artist impression of JAXA’s MMX spacecraft around Mars (JAXA).
Japan in planning to launch a mission to visit the two moons of Mars in 2024. The spacecraft will touchdown on the surface of Phobos, gathering a sample to bring back to Earth. But what is so important about a moon the size of a city?
Unlike the spherical shape of the Earth’s moon, the Martian moons resemble asteroids, with an asymmetric lumpy potato structure. This highlights one of the first mysteries about the pair: how did they form?
Light reflected from the moons’ surface gives clues to their composition, as different minerals absorb particular wavelengths of radiation. If an object reflects more light at longer wavelengths, it is said to have a spectra with a red slope. This is true of both Phobos and Deimos, which appear very dark in visible light but reflect more strongly in longer near-infrared wavelengths. It is also true of D-type asteroids, which orbit the sun in the outer edge of the asteroid belt that sits between Mars and Jupiter.
The similarities between both their lumpy shape and reflected light has led to speculation that the two moons are captured asteroids, snagged by Mars’s ...