The moonlet Deimos is made of the same type of material as Mars, the latest observations suggest.

Credit: Emirates Mars Mission

The United Arab Emirates’ space probe Hope has taken the first high-resolution images of the farside of Mars’s moonlet Deimos. The observations add weight to the theory that Deimos formed together with Mars, rather than as an asteroid that was captured in the planet’s orbit, mission scientists say.

Hope, formally known as the Emirates Mars Mission (EMM), performed a fly-by — the first of many — on 10 March. EMM science lead Hessa Al Matroushi recalls the excitement when the first images streamed in, looking down at the 12.4-kilometre-wide moonlet. “Mars was in the background — and that was just mind blowing, honestly,” says Al Matroushi, who is at the Mohammed Bin Rashid Space Centre in Dubai, United Arab Emirates. She reported the results at the European Geosciences Union meeting in Vienna on 24 April.

Like Earth’s Moon, Deimos is tidally locked to its planet, meaning that any observations from a low Mars orbit or the planet’s surface are always of the same side of the moonlet.

Animation of 3D images of Deimos during close fly-bys.

Hope’s closest encounter with Deimos reveals its irregular shape and asteroid pockmarks.

Credit: Emirates Mars Mission

But compared with the flotilla of missions that have visited the red planet, Hope has an unusually high and elongated orbit, which reaches more than 40,000 kilometres above Mars’s surface at its highest point, explains Al Matroushi. This enables it to observe Deimos from above and to image its farside. (EMM is unable to visit Mars’s other natural satellite, Phobos, which circles the planet at less than 10,000 kilometres from the surface — lower than the lowest point in the probe’s orbit.)

During the 10 March fly-by, the mission team used all three onboard instruments to take readings spanning from the infrared to the extreme ultraviolet. The relatively flat spectrum the scientists saw is suggestive of the type of material seen on Mars’s surface, rather than the carbon-rich rock often found in asteroids, suggesting that Deimos was formed from the same material as the planet. “If there were carbon or organics, we would see spikes in specific wavelengths,” she says.

3D image of Deimos captured during close fly-bys.

The Hope probe is the first to fly by Deimos. It captured stereo images during its closest pass, seen here in a 3D picture best viewed with red–cyan anaglyph glasses.

Credit: Emirates Mars Mission

The 1.35-tonne, US$200-million spacecraft launched on a Japanese rocket in July 2020 and arrived at Mars in February 2021. With frequent observations of Mars’s atmosphere, its main science goal was to study seasonal variations in the planet’s atmosphere and weather patterns. But once that phase was concluded with propellant to spare, mission control fired the onboard thrusters in a manoeuvre that allows the spacecraft to intersect with Deimos’s orbit multiple times. “We don’t want to get a one-time observation of Deimos,” says Al Matroushi. “We knew we wanted more.”