Hera mission and CubeSats in orbit. Credit: ESA–ScienceOffice.org.

The European Space Agency (ESA) has revealed plans to launch a mission to examine a binary asteroid system, Didymos, with the aim of helping protect the Earth from possible collision.

Named after the Greek goddess of marriage, Hera, the proposed mission will fly to the near-Earth asteroids. This includes a 780m diameter main body orbited by a 160m moon, called Didymoon, about the size of the Great Pyramid of Giza.

Expected to reach Didymos by 2026, Hera will primarily focus on Didymoon.

The mission will involve high-resolution visual, laser and radio science mapping of the moon to build detailed maps of its surface and interior structure.

Hera manager Ian Carnelli said: “Such a binary asteroid system is the perfect testbed for a planetary defence experiment but is also an entirely new environment for asteroid investigations.

“Essential information will be missing following the DART impact, which is where Hera comes in.”

“Although binaries make up 15% of all known asteroids, they have never been explored before, and we anticipate many surprises.

“The extremely low-gravity environment also presents new challenges to the guidance and navigation systems. Fortunately we can count on the unique experience of ESA’s Rosetta operations team which is an incredible asset for the Hera mission.”

Before Hera reaches Didymos, the current course of Didymoon is expected to be shifted by a Nasa mission named Double Asteroid Redirection Test (DART).

Currently under development, DART is predicted to collide with Didymoon by October 2022. This will be the first mission to move an object in the solar system in a measurable way.

Carnelli added: “Essential information will be missing following the DART impact, which is where Hera comes in.

“Hera’s close-up survey will give us the mass of Didymoon, the shape of the crater, as well as physical and dynamical properties of Didymoon.

“This key data gathered by Hera will turn a grand but one-off experiment into a well-understood planetary defence technique: one that could in principle be repeated if we ever need to stop an incoming asteroid.”

Images captured by Hera will be used to track key landmarks on the surface on Didymain, such as boulders or craters.

Hera will also measure the crater left by DART to a resolution of 10cm.