European Spacecraft Captures Rare Images of Mars' Moon Deimos During Asteroid Mission

On the way to investigate the scene of a historic asteroid collision, a European spacecraft swung by Mars and captured rare images of the red planet's mysterious small moon Deimos, the European Space Agency said Thursday. Europe's HERA mission is aiming to find out how much of an impact a NASA spacecraft made when it deliberately smashed into an asteroid in 2022 in the first test of our planetary defenses. But HERA will not reach the asteroid — which is 11 million kilometers from Earth in the asteroid belt between Mars and Jupiter — until late 2026.

On the long voyage there, the spacecraft swung around Mars on Wednesday. The spacecraft used the planet's gravity to get a "kick" that also changed its direction and saved fuel, mission analyst Pablo Munoz told a press conference. For an hour, HERA flew as close as 5,600 kilometers from the Martian surface, at a speed of 33,480 kilometers an hour. It used the opportunity to test some of its scientific instruments, snapping around 600 pictures, including rare ones of Deimos.

The lumpy, 12.5-kilometer-wide moon is the smaller and less well-known of the two moons of Mars. Exactly how Deimos and the bigger Phobos were formed remains a matter of debate. Some scientists believe they were once asteroids that were captured in the gravity of Mars, while others think they could have been shot from a massive impact on the surface. The new images add "another piece of the puzzle" to efforts to determine their origin, Marcel Popescu of the Astronomical Institute of the Romanian Academy said.

There are hopes that data from HERA's "HyperScout" and thermal infrared imagers — which observe colors beyond the limits of the human eye — will shed light on this mystery by discovering more about the moon's composition. Those infrared imagers are why the red planet appears blue in some of the photos.

Next, HERA will turn its focus back to the asteroid Dimorphos. When NASA's DART mission smashed into Dimorphos in 2022, it shortened the 160-meter-wide asteroid's orbit around its big brother Didymos by 33 minutes. Although Dimorphos itself posed no threat to Earth, HERA intends to discover whether this technique could be an effective way for Earth to defend itself against possibly existence-threatening asteroids in the future.

Space agencies have working to ramp up Earth's planetary defenses, monitoring for potential threats so they can be dealt with as soon as possible. Earlier this year, a newly discovered asteroid capable of destroying a city was briefly given a more than 3% chance of hitting Earth in 2032. However further observations sent the chances of a direct hit back down to nearly zero.

Richard Moissl, head of the ESA's planetary defense office, said that asteroid, 2024 YR, followed a pattern that will become more common. As we get better at scanning the skies, "we will discover asteroids at a higher rate," he said.

The ESA is developing a second planetary defense mission to observe the 350-metre-wide asteroid Apophis, which will fly just 32,000 kilometers from Earth on April 13, 2029. If approved by the ESA's ministerial council, the Ramses mission will launch in 2028, reaching the asteroid two months before it approaches Earth.