Hera begins asteroid survey after NASA's planetary defence test

The European Space Agency (ESA) says its Hera spacecraft has started close observations of the asteroid Didymos and its moonlet Dimorphos. The mission is investigating the effects of NASA's 2022 collision with Dimorphos, which tested a possible method of planetary defence.

Hera is operating between 25 kilometres and 30 kilometres from the pair. Launched in 2024 and comparable in size to a small car, the spacecraft will approach to a distance of 20 kilometres. It carries 25 scientific instruments and two shoebox-sized Cubesats, which will examine Dimorphos at closer range and try to land on it.

NASA's Double Asteroid Redirection Test, known as Dart, shortened the time Dimorphos takes to orbit Didymos. The impact also slightly altered the moonlet's path around the sun. Rubble and boulders thrown out by the collision added to its momentum, leaving a trail of debris stretching more than 10,000 kilometres through space for months.

Scientists say some debris may remain nearby. Dimorphos has an estimated diameter of 151 metres, while Didymos measures roughly 780 metres across.