Hera Reaches the Didymos Asteroids
Hera Reaches the Didymos Asteroids
Hera is a European Space Agency mission heading to the asteroid Didymos and its small moon Dimorphos. This is the same system that NASA visited with the DART mission in 2022. DART intentionally crashed into Dimorphos to test whether a spacecraft could change an asteroid's motion. The impact changed the time Dimorphos takes to orbit Didymos. Hera is being sent back to study the result in much more detail. As of 1 October 2026, this article still has to stay hidden until ESA confirms the planned rendezvous.
Why scientists want another look
Scientists already know that DART changed Dimorphos's orbit. What they do not know as well is exactly how the asteroid responded inside and on its surface. A direct visit can measure details that are difficult to see from Earth. Hera can study the shape, mass and surface of Dimorphos. It can also look closely at the area changed by the DART collision. Those measurements can make future asteroid-deflection plans more accurate.
The mass of Dimorphos matters
Changing an object's motion depends partly on how massive that object is. Researchers therefore need a good estimate of Dimorphos's mass. Hera can use the motion of the asteroid system to help calculate that value. A better mass estimate makes it easier to understand how much momentum DART transferred. That tells researchers more about how effective the impact really was. It also improves models used for other asteroids that may have very different sizes and structures.
The impact site can reveal what happened
The surface of Dimorphos may record the DART collision in several ways. There may be a crater, a reshaped area or large amounts of moved material. The exact result depends on how tightly the asteroid's rocks are held together. A loose pile of rubble can respond very differently from a strong solid body. Hera's cameras will map the surface at much higher detail than Earth-based telescopes can provide. That will let scientists compare the real result with the models made before and after DART.
Two small spacecraft will help
Hera also carries two small CubeSats called Milani and Juventas. These spacecraft are much smaller than the main Hera probe. Milani is designed to study the surface and dust around the asteroid system. Juventas carries radar that can help probe the inside of Dimorphos. That may show whether the moon is packed tightly or contains many gaps and loose blocks. Together, the three spacecraft can study both the outside and the inside of the target.
Why this matters for planetary defense
Planetary defense is about finding dangerous asteroids early and knowing what we could do if one threatened Earth. DART showed that a spacecraft impact can change the orbit of a small asteroid moon. Hera is meant to turn that demonstration into a better understood experiment. Scientists want to know which parts of the result would apply to other asteroid shapes and materials. No single asteroid can represent every possible future target. Paleon will update this article only after ESA confirms the rendezvous instead of treating a planned mission date as a completed event.