Deimos is in the limelight. The United Arab Emirates’s Hope orbiter, part of the Emirates Mars Mission (EMM), has flown just 100 kilometres from the surface of the Red Planet’s smaller moon and taken extraordinarily detailed observations.
The measurements included pictures and ultraviolet and infrared observations, with data on areas of Deimos that have never been examined in any detail before. All this allowed the orbiter, which launched in July 2020 and entered orbit around Mars in February 2021, to shed light on how Deimos and the other, larger Martian moon, Phobos, formed.
“We are unsure of the origins of both,” said Hessa Al Matroushi, EMM science lead, in a statement. “One long-standing theory is that they are captured asteroids, but there are unresolved questions about their composition.”
The orbiter’s observations of both moons indicate that explanation is unlikely. Their compositions seem to be more similar to Mars than to asteroids, pointing to the idea that they were either formed from Mars itself or from the same reservoir of planetary material.
Hope is in a unique position to observe Deimos in most detail. Spacecraft we send to Mars usually orbit the planet relatively closely for the sake of precise observations of its surface, but Deimos circles it at an average distance of 23,460 kilometres, much too high for such craft to see it in any detail
The Hope orbiter, though, has a wide orbit around Mars – between 20,000 and 43,000 kilometres up – so that it can observe huge swathes of the planet’s atmosphere in one go. This has allowed it to get up close and personal with Deimos.
Several more close passes to this moon are planned over the course of the next year, so we should get even more clues to its composition and possible origin.
The mission was originally intended to last only one Martian year, which is nearly two Earth years, but the UAE recently announced that it will be extended by another Earth year so that it can continue its investigations of Mars and its moons.