What the Hera mission could reveal about the asteroid impacted by NASA to deflect it

Remember. In September 2022, DartDarta probe launched by NASA in November 2021, collided with the asteroid Dimorphos, a small 160-meter moon orbiting the asteroid Didymos. The aim of the maneuver was to check whether an impact against an asteroid could modify its orbit, and therefore its trajectory, and thus verify the operational feasibility of a planetary defense technique in the event that an asteroid heading straight forward would be detected early enough. on Earth.

The maneuver was successful and the impact changed the trajectory of the asteroid! Concretely, before the impact, it took 11 hours 55 minutes for Dimorphos to go around its parent asteroid. Duration which increased to 11 hours 23 minutes, thanks to the collision with the Dart probe, a shortening of 32 minutes! It’s not much, but over a distance of several million kilometers it’s enough to allow an object to avoid colliding with another.

That said, disrupting the trajectory of the asteroid “ will not be sufficient to draw conclusions for our models », explained to us in September 2022 Patrick Michel, research director at the CNRS at the Côte d’Azur Observatory, scientific manager of HeraHera and coordinator of Aida cooperation (Dart + Hera). To understand the characteristics of the impact such as size, depth and quantity of mattermatter ejected, you need to know the “ structural properties of the asteroid which could be aggregated or compact and solidsolid “, but also ” the nature of the terrain struck which can be sandy, rocky or strewn with stones and its structure “, he specifies.

A satellite to see what happened on site

And this is the role of the Hera satellite of theEuropean Space AgencyEuropean Space Agency (ESA) which will be launched in a few days by a launcherlauncher Falcon 9Falcon 9 of SpaceXSpaceX. It will join Didymos at the end of December 2026, four years after the impact of Dart. Note that initially it was planned for Hera to arrive shortly before Dart’s impact, in order to observe the collision live and the formation of the crater, just as it should have been launched by an Ariane 6. No comment.

Despite everything, this late arrival will be “ without consequences on the measures we wish to carry out “. Indeed, the properties that Hera must measure “ will not have time to change for four years “. The size of the crater formed which will provide us with crucial information about the mechanical properties and subsurface composition of the asteroid ”, as well as the “ modification of Dimorphos’ orbit around the main body » will indeed be those following the impact of Dart.

The whole point of the Hera mission is to “ measure the result of the impact, that is to say the quantity of movements actually transferred to Dimorphos upon impact and damage sustained on the surface “. All of its data will make it possible to “ verify the relevance of the techniqueimpactor kinetics, its maturity, and to validate the digital simulations impact on the scale of an asteroid “. It is also the “ first time we will have information on the internal structure of an asteroid ».

Note that Hera will perform technology demonstrations, including the deployment of the first CubeSatsCubeSats of ESA intended for deep space. The Milani satellite will carry out spectral observations of the surface, while Juventas will carry out the first ever surveys of the interior of an asteroid. These two satellites, which could eventually land on Didymoon, will fly over the asteroid at a distance much closer than that of Hera.

With Hera, its observational data is expected to provide a documented asteroid-scale impact experience to protect Earth from near-Earth object (NEO) impacts.