Hera separates its targets ahead of the Dimorphos survey
· BehindLines newsroom
Europe's Hera spacecraft is starting to distinguish the two bodies it will investigate. In an announcement on 27 October, the European Space Agency says its camera can now separate Didymos from its smaller companion, Dimorphos. The latter still occupies about one pixel in the image presented. This step identifies the two targets; it does not yet reveal in detail any surface changes caused by the American DART mission.
A test with a measured effect on the orbit
In September 2022, DART deliberately struck Dimorphos, which orbits Didymos. NASA subsequently confirmed through telescope observations that the collision had shortened the time needed to complete that orbit. The aim was to test a deflection method, rather than respond to an immediate threat: the agency said neither asteroid posed a danger to Earth, before or after the test.
The American assessment also distinguished the direct collision from the effect of the debris thrown out. Its ejection increased the push received by Dimorphos. Understanding the result therefore required studying the properties of the material as well as the collision itself.
Comparing simulations with close observations
A study by Sabina Raducan and colleagues, submitted to arXiv in March 2024, explores this question using numerical simulations. The configurations that reproduce the observations suggest a weakly cohesive body made up of an accumulation of debris. In those calculations, the impact can transform the entire asteroid rather than leave only a clearly defined crater.
That scenario remains an interpretation to be checked. A simulation consistent with the data is not a photograph of the current surface. The researchers describe Hera's future observations as a way to compare their results with reality.
ESA says detailed images of Dimorphos will be unveiled on 25 November. As of 28 October, they are still awaited. The value of this stepwise approach is to connect three levels of evidence: an orbital change already measured, models to explain it, and close observations intended to distinguish between them.