First close-up of Mars’ unknown moon Deimos

The UAE’s Hope space probe has captured the first high-resolution images of the far side of Mars’ moon Deimos. Mission scientists say the observations add weight to the theory that Deimos formed with Mars rather than an asteroid captured in the planet’s orbit.

Hope, officially known as the Emirates Mars Mission (EMM), performed a flyby — the first of many — on March 10. Hessa Al Matrooshi, science lead at EMM, remembers the excitement when the first images streamed in, as she looked down at the tiny 12.4-kilometre-wide moon. “Mars was in the background — and that was amazing, honestly,” says Al Matrooshi, who works at the Mohammed bin Rashid Space Center in Dubai, United Arab Emirates. She reported the findings at the European Geosciences Union meeting in Vienna on April 24.

Like Earth’s moon, Deimos is phase-locked to its planet, which means that any observations from a low orbit of Mars or the planet’s surface are always from the same side of the young moon.

But compared to the fleet of missions that visited the Red Planet, Hope has an unusually high and extended orbit, which reaches more than 40,000 km above the surface of Mars at its highest point, Al Matrooshi explains. This enables it to observe Deimos from above and photograph its far side. (EMM is unable to visit Mars’ other natural satellite, Phobos, which orbits the planet less than 10,000 kilometers from the surface—less than the lowest point in the probe’s orbit.)

During the March 10 flyby, the mission team used all three instruments onboard to take readings that stretched from infrared to extreme ultraviolet. The relatively flat spectrum the scientists saw indicates the type of material seen on Mars, not the carbon-rich rocks often found in asteroids, indicating that Deimos may have formed from the same material as the planet. “If there’s carbon or organics, we’ll see spikes at specific wavelengths,” she says.

The 1.35-ton, US$200 million spacecraft was launched on a Japanese rocket in July 2020 and arrived at Mars in February 2021. With frequent observations of the Martian atmosphere, its main scientific goal has been to study seasonal changes in the planet’s atmosphere and weather patterns. But once this stage was completed with propellant supplied, mission control fired the onboard thrusters in a maneuver that allowed the spacecraft to intersect Deimos’ orbit several times. “We don’t want to get a one-time view of Demos,” says Al Matrooshi. “We knew we wanted more.”