United Arab Emirates space probe Hope has taken the first high-resolution images of the far side of Deimos, the 12.4-kilometre-wide moonlet which orbits Mars.
Like Earth’s Moon, Deimos is tidally locked to its host planet, meaning that observations from the Martian surface or low orbit always reveal the same side of the moonlet. Hope, formally known as the Emirates Mars Mission (EMM), performed its fly-by – the first of many planned – on March 10.
The images suggest that Deimos formed from the same material as Mars, rather than being a rogue asteroid caught in the planet’s gravitational field.
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Deimos (named after the Greek god of dread and terror) orbits on average more than 23,000 kilometres above the Red Planet’s surface. Mars’s other natural satellite, Phobos (roughly 20 kilometres wide), orbits at less than 10,000 kilometres above the planet, lower than Hope’s lowest orbit, making it impossible for the probe to visit Phobos as well.
Hope’s orbit is unusual compared to other missions that have visited Mars. It’s unusually high and elongated orbit, which reaches more than 40,000 kilometres at its height, makes the EMM uniquely positioned to fill gaps in our knowledge about Mars’s little-understood moonlet.
On-board sensors during the drive by camera shoot also took readings from the infrared to the extreme ultraviolet to gain insight into the chemical makeup of Deimos.
The relatively flat spectrum is similar to the type of material seen on Mars itself, rather than the carbon-rich rock often found in satellites.
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Hope was launched on a Japanese rocket in July 2020 and arrived at its destination in orbit around Mars in February 2021.
The 1.35-tonne spacecraft has been mainly used to study Martian weather, but has now been brought through the firing of on-board thrusters into the path of Deimos’s orbit, and will intersect with the moonlet multiple times.
“We don’t want to get a one-time observation of Deimos,” says EMM science lead Hessa Al Matroushi in a Nature news article. “We knew we wanted more.”