ESA’s Hera Sees a Sharp Ridge on Asteroid Didymos From 56 km
ESA's Hera spacecraft imaged Didymos from 56 km and found a sharp equatorial ridge on the 780-meter asteroid. Detailed images are due Nov. 25.
The European Space Agency’s Hera spacecraft has photographed the Didymos asteroid system from 56 km away and found a surprisingly sharp ridge around the equator of the main asteroid, ESA said. Didymos is 780 meters across, and the image shows one face of it.
A small part of Dimorphos, the 151-meter moonlet that orbits Didymos, peeks out near the top of the larger body. ESA calls the picture another early preview and says detailed images of both asteroids will be unveiled on Nov. 25.
What the picture shows
According to ESA, the surface of Didymos has large boulders, smoother regions and the equatorial ridge. Most of Dimorphos is hidden behind its parent. It orbits a little more than a kilometer away, and a few boulders are visible along its top side.
A spin fast enough to nearly tear it apart
Didymos is shaped like a spinning top and rotates every 2.2 hours, which ESA says is fast enough that the asteroid is close to coming apart. The agency suggests the ridge may exist because of that spin. Numerical models of fast-spinning asteroids indicate that the rotation can make surface material flow from higher latitudes down toward the equator. ESA adds that some material might also be shed from the larger asteroid, which could account for the existence of the moonlet.
These explanations come from models and are presented as possibilities, not as results confirmed by the new image.
The impact Hera is following up
On Sept. 26, 2022, NASA’s 580-kg DART spacecraft struck Dimorphos at 6.1 km/s in a planetary defense experiment. The collision sent debris into space and slowed the asteroid’s orbit by around 33 minutes.
ESA says important unknowns remain before this kinetic impact method, which tries to change an asteroid’s path by hitting it with a spacecraft, is well understood. Scientists want to know what the impact did to the asteroid itself, and whether it left a crater or reshaped the whole body. They also want the precise makeup, structure and mass of Dimorphos, and the properties that explain a deflection much greater than impact simulations predicted.
What this means for planetary defense
Hera is ESA’s first planetary defense mission, and the questions above are the ones the agency says stand between the DART test and a well-understood technique.
Over the coming months Hera will carry out a close-up “crash site investigation” of Dimorphos using multiple instruments. It will deploy a pair of shoebox-sized CubeSats for a still closer survey, and the mission is meant to progress eventually to landing. The next dated step is the Nov. 25 release of detailed images of both asteroids.
Source: European Space Agency
