By BlueShift and AFP | 2025-03-14

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 (ESA) said March 13.

Launched on October 7, 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-ever test of Earth's planetary defenses.

But Hera will not reach the asteroid -- which is 11 million km from Earth in the asteroid belt between Mars and Jupiter -- until late 2026.

On the long voyage there, the spacecraft slingshotted around Mars on March 12.

The spacecraft used the planet's gravity to get a "kick" that changed its direction and saved fuel, mission analyst Pablo Munoz told a press conference.

For an hour, Hera flew as close as 5,600km from the Martian surface, at a speed of 33,480 km/h.

It used the opportunity to test some of its scientific instruments, snapping about 600 pictures, including rare ones of Deimos.

Three instruments were used during the flyby: Hera's black and white 1020×1020 pixel Asteroid Framing Camera, Hera's Hyperscout H hyperspectral imager and Hera's Thermal Infrared Imager, supplied by the Japan Aerospace Exploration Agency (JAXA).

"These instruments have been tried out before, during Hera's departure from Earth," ESA's Hera mission scientist Michael Kueppers said in a statement, "but this is the first time that we have employed them on a small distant moon for which we still lack knowledge -- demonstrating their excellent performance in the process!"

'Piece of the puzzle'

Deimos, the lumpy, 12.5km-wide moon, is the smaller and lesser-known of the two moons of Mars.

Exactly how Deimos and the bigger Phobos were formed remains a matter of debate.

Some scientists say they were once asteroids that were captured in the gravity of Mars, while others theorize 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, said Marcel Popescu of the Astronomical Institute of the Romanian Academy.

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.

"Results from the Deimos close encounter should help guide operational planning for next year's Martian Moons eXploration Mission, MMX, being led by JAXA in collaboration with NASA, the French space agency CNES, the German Aerospace Center (DLR), and ESA," the ESA statement said.

"MMX will not only collect detailed measurements of both Martian moons but also land on Phobos to collect a sample and return it to Earth for analysis."

Bolstering planetary defense

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.

Though Dimorphos itself posed no threat to Earth, Hera is meant 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 been 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, astronomers briefly gave a newly discovered asteroid capable of destroying a city 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.

That asteroid, 2024 YR, followed a pattern that will become more common, said Richard Moissl, director of the ESA's planetary defense office.

As humanity becomes better at scanning the skies, "we will discover asteroids at a higher rate," he said in February, according to AFP.

The ESA is developing a second planetary defense mission to observe the 350-meter-wide asteroid Apophis, which will fly just 32,000km 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.