For most of the journey since its October 2024 launch, the European Space Agency's Hera spacecraft has seen its destination as a single dot. That changed on the evening of 18 October, when Hera's Asteroid Framing Camera picked out two objects instead of one: the asteroid Didymos and, beside it, its small moon Dimorphos.
ESA has published the image, and Space.com reported on it on 3 November. According to ESA, the monochromatic camera took the picture from 1,280 km away from the pair, which ESA puts at about 197 million km from Earth.
One pixel, but a separate one
It isn't a pretty picture yet. ESA says Dimorphos covers only about one pixel, but that pixel sits clearly apart from Didymos.
"With this image the smaller Dimorphos asteroid becomes visible for the first time," Hera project scientist Michael Kueppers said in ESA's release. Space.com quotes him going further: before this image, the spacecraft "was still resolving the Didymos system as a single dot."
ESA's mission manager, Ian Carnelli, said the team is now seeing the double asteroid system through Hera's own eyes. Space.com quotes him on what comes next: "Our views will grow much sharper as Hera comes closer," with the first detailed images of Dimorphos to be unveiled on 25 November. ESA gives the same date.
Why this little moon matters
Dimorphos is the asteroid NASA hit on purpose. ESA says NASA's DART spacecraft struck it on 26 September 2022 at 6.1 km/s. The impact threw a plume of debris across some 10,000 km of space and changed Dimorphos's orbit around Didymos by around 33 minutes. That makes it, in ESA's words, the first object in the Solar System whose orbit humans have measurably changed.
DART proved that a spacecraft can nudge an asteroid. It couldn't stay behind to show what the impact did. That job falls to Hera, which Space.com describes as a planetary defence mission sent to survey the damage and refine our understanding of the impact. ESA lists the open questions: whether DART left a crater, and what Dimorphos's structure, mass and composition are.
The two rocks are not large by asteroid standards. ESA gives Dimorphos as 151 m across, about the size of the Great Pyramid of Giza, and Didymos as 780 m in diameter, a little smaller than Dubai's Burj Khalifa. The pair orbit an average of 1.15 km apart, ESA says, with Dimorphos moving at about 18 cm per second.
Slowing down for the visit
Getting this close took some braking. ESA says two thruster firings a week apart, earlier in October, slowed Hera to 20 m/s relative to the asteroids. Space.com notes that Hera launched on a SpaceX Falcon 9 in October 2024 and carries 12 payloads for its follow-up observations.
Over the coming months ESA plans what it calls a close-up "crash site investigation" of Dimorphos with several instruments. Hera will also release two shoebox-sized CubeSats to survey the asteroid more closely. Space.com says the pair are meant for a closer look and an eventual landing on Dimorphos.
What to watch for
The next date to note is 25 November, when ESA says it will publish the first detailed images of Dimorphos. Those should give a much sharper look at the asteroid DART hit.
Finn's take: There's something quietly satisfying about a mission whose big moment is one pixel sitting apart from another. Almost everything about planetary defence happens slowly and far away, and this picture is a fair reminder of that. The proper look at Dimorphos comes on 25 November, and I'd rather see it then than have someone guess now.
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