Europe's Hera probe heads for asteroid collision site as scientists weigh deflection risks ahead of Asteroid Day

The Hera mission and its target

Ahead of International Asteroid Day on 30 June, the European Space Agency's Hera mission is approaching the double-asteroid system Didymos-Dimorphos. The probe, controlled from ESA's centre in Darmstadt, Germany, is scheduled to arrive in November. It follows NASA's Double Asteroid Redirection Test (DART), which slammed a probe into Dimorphos at roughly 6.6 kilometres per second in September 2022.

We are now entering a new era for humanity, in which we could have the ability to protect ourselves against an asteroid impact.

The DART impact measurably altered Dimorphos's orbit around the larger Didymos. Hera's job is to deliver precise data on the asteroid's composition, density, size, and shape, resolving what exactly the crash left behind.

What the impact may have done

Richard Moissl, ESA's lead coordinator for asteroid defence in Darmstadt, said the size of the dust cloud from the DART collision was surprising. The crater's appearance remains unknown.

Classically you would expect a crater to be there now. But it could also look like it's been nibbled on.

Detlef Koschny, professor of lunar and planetary exploration at the Technical University of Munich, raised a deeper concern: the asteroid may have deformed entirely. Applying too much force during a deflection attempt could break an asteroid apart rather than push it aside, sending fragments still on a collision course with Earth.

If I want to deflect an asteroid, that is a very critical matter.

The Ramses mission and Apophis flyby

A follow-on mission called Ramses (Rapid Apophis Mission for Space Safety) is planned for 2029. It will study the roughly 400-metre asteroid Apophis, which will pass just 32,000 kilometres from Earth on Friday, 13 April 2029. By comparison, the Moon averages 384,400 kilometres away. Moissl confirmed that all industrial contracts for Ramses have been signed and key milestones reached.

We want to see what it looks like before it gets properly shaken up by Earth's tidal forces.

Koschny noted that scientists hope to observe changes on Apophis during the close pass, when terrestrial gravitational forces could alter its surface. An impact is ruled out for at least the next 100 years, and no deflection is planned. The asteroid will be visible to the naked eye.

Future detection challenges

Asteroids approaching from the direction of the Sun remain difficult to spot with current technology. ESA is planning an infrared telescope to address this blind spot, though details remain at an early stage. The combined data from DART, Hera, and Ramses aims to build a reliable planetary defence playbook.