This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The European Space Agency's Hera spacecraft for planetary defense has resolved its two target asteroids separately for the first time, revealing the binary nature of the Didymos system, currently some 197 million km (122 million miles) away from Earth. Hera imaged Didymos and Dimorphos with its monochromatic Asteroid Framing Camera on the evening of Friday, Oct. 18, at a distance of 1,280 km (795 miles) from the asteroid pair.
"With this image the smaller Dimorphos asteroid becomes visible for the first time," explains Michael Kueppers. "Before this acquisition the spacecraft was still resolving the Didymos system as a single dot. But now, even though Dimorphos is made up of only around one pixel in this initial image, it is clearly well separated from its parent body." This first image came following the success of Hera's braking maneuvers earlier this month.
A pair of thruster firings a week apart slowed the spacecraft to just 20 m/s (45 miles per hour) relative to its two target asteroids, allowing it to come gradually closer on a fine-tuned basis. At 151 m (495 feet) across, Dimorphos is about the size of the Great Pyramid of Giza, while the 780-m-diameter (2,560-foot-diameter) Didymos asteroid is a little smaller than Dubai's Burj Khalifa skyscraper, the tallest building in the world. The pair orbit an average 1.15 km (0.71 miles) apart from each other, with Dimorphos orbiting its parent at about 18 cm/s (7.1 inches per second).
"For the first time we are seeing through Hera's own eyes the double asteroid system that the mission was designed and built for," adds mission manager Ian Carnelli. "Our views will grow much sharper as Hera comes closer. We will unveil the first detailed images of Dimorphos—the first object in the solar system to have had its orbit measurably shifted by human action—on Nov. 25." On Sept. 26, 2022, Dimorphos became the subject of a grand-scale planetary defense experiment when NASA's DART spacecraft impacted the smaller asteroid at a velocity of 6.1 km/s (3.8 miles per second).
The resulting collision sent out a plume of debris across 10,000 km (6,200 miles) of space while also slowing the asteroid's orbit by around 33 minutes. But key unknowns remain to turn this "kinetic impact" method into a well-understood planetary defense technique: What did the impact do to the asteroid itself? Did it leave a crater, or reshape the asteroid body entirely?
What is the precise makeup, structure and mass of Dimorphos—and which properties explain a deflection so much greater than impact simulations predicted? Over the coming months Hera will perform a close-up "crash site investigation" of Dimorphos, harnessing multiple instruments and deploying a pair of shoebox-sized CubeSats for a still closer survey, eventually progressing to landing. BA art history, MA material culture.
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