The Hera image also shows a small part of the moonlet Dimorphos above the larger asteroid. The European Space Agency plans to unveil detailed images of both on 25 November.
A new image from the European Space Agency’s Hera mission shows large boulders, smoother regions and a sharp ridge around the equator of Didymos. A small part of its moonlet, Dimorphos, peeks out near the top, with a few boulders visible along its upper edge.
Hera is following up on NASA’s planetary-defense experiment of 26 September 2022, when its DART spacecraft struck Dimorphos. The collision shortened the moonlet’s orbital period by around 33 minutes, ESA says.
Analysis
Didymos is 780 meters across and rotates every 2.2 hours, a speed ESA describes as close to the point at which it could come apart. Dimorphos is 151 meters across and orbits a little more than a kilometer from the larger asteroid.
In its description of the image, ESA says models of fast-spinning asteroids suggest that rotation could move surface material from higher latitudes toward the equator, potentially explaining the ridge. The agency also suggests that material shed from Didymos could have formed Dimorphos. Neither process is shown in the image.
ESA says it remains unclear whether DART left a crater or reshaped Dimorphos entirely. The moonlet’s precise composition, structure and mass are also unknown; the agency wants to understand which properties explain why the deflection was much greater than simulations predicted. Those answers could make the technique of deflecting an asteroid by hitting it better understood.
ESA plans to unveil detailed images of both asteroids on 25 November. Over the coming months, Hera will investigate Dimorphos with multiple instruments and deploy two shoebox-sized CubeSats, or small satellites, for a closer survey before eventually progressing to landing activities.
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