Summary
ESA says its Hera spacecraft has imaged the asteroids Didymos and Dimorphos as separate objects for the first time. The image was taken from 1,280 km away as Hera approaches the pair to examine the site of NASA’s DART impact.
The European Space Agency (ESA) says its Hera spacecraft has resolved the asteroids Didymos and Dimorphos as two separate objects for the first time. Hera captured the image with its monochromatic Asteroid Framing Camera from 1,280 km away, as it approached the binary asteroid system, then about 197 million km from Earth.
Dimorphos appears as roughly one pixel in this first image, but is visibly separated from the much larger Didymos. The observation marks a new stage in Hera’s journey from tracking the pair as a single point of light to studying them individually.
A binary asteroid comes into view
Didymos is about 780 metres in diameter; its smaller companion, Dimorphos, is about 151 metres across. The two orbit an average of 1.15 km apart, with Dimorphos moving around Didymos at about 18 cm per second.
ESA says the image followed a pair of braking manoeuvres, performed a week apart, that brought Hera’s speed relative to the asteroids down to 20 metres per second. The controlled approach allows the spacecraft to move closer gradually. As the distance decreases, its images are expected to show more detail.
Following up NASA’s DART impact
Hera is investigating the consequences of NASA’s 2022 Double Asteroid Redirection Test (DART). On 26 September 2022, DART struck Dimorphos at 6.1 km per second. ESA reports that the impact produced a debris plume extending across 10,000 km of space and changed Dimorphos’s orbit by about 33 minutes.
The collision demonstrated an asteroid-deflection approach called a kinetic impact: a spacecraft collides with an asteroid to change its motion. Hera’s close-up investigation is intended to help explain how the impact affected Dimorphos, including whether it formed a crater or substantially reshaped the asteroid. The mission will also study the asteroid’s composition, structure and mass—properties that help interpret why the measured deflection differed from impact simulations.
ESA says Hera will use several instruments and deploy two shoebox-sized CubeSats for closer observations, with the mission eventually progressing to landing. The first separate image is an early view, rather than the detailed survey: Dimorphos occupies only about one pixel in it. ESA said the first detailed images were planned for 25 November.