For Science, it is not a question of “if”, but of “when” an asteroid will reach Earth – and long-term planning is at the heart of the planet’s defense to prevent catastrophe. Now, it is the turn of the European Space Agency (ESA), which has signed a contract of almost 130 million euros to build and launch its first planetary defense mission: Hera.
Named after the Greek goddess of marriage, the probe is due to launch in October 2024 and will be the first to travel to a pair known as Didymos (still little studied, they are binary systems that make up 15% of all known asteroids ).
The main body (Didymos A) is 780 meters in diameter and is orbited by a 160 meter moon (Didymos B, formally called Dimorphos).
Hera will be observing the work of NASA’s small Double Asteroid Redirect Test (DART) spacecraft. Scheduled for launch in July 2021, she will purposely hit the smaller body.
DART’s impact on Dimorphos is expected to occur in September 2022. The expected result is that it will be able to alter its orbit around Didymos, as well as create a substantial crater.
Hera will arrive at Didymos in late 2026 and will navigate around the system for at least 6 months, collecting data on the composition of the affected body and identifying changes in the trajectory of the larger asteroid, working together with telescopes on Earth. If the trajectory of the system is proven to have changed, the experiment will serve as the basis for an asteroid deflection technique.
However, this will not be the European probe’s only job: it will also deploy 2 cubesats (miniature satellites built from 10 cm boxes) inside the Dimorphos impact crater – they will be the first European spacecraft of the type in deep space.
In our solar system, science estimates that there are about 25,000 large asteroids – only about 8,000 have been identified so far. Therefore, the international community joined forces through the Asteroid Impact & Deflection Assessment (“Assessment of the impact and deflection of the asteroid” – AIDA) in the search for an effective plan in case an object threatens the Earth. The use of DART is one of them.
It is estimated that the impact with Dimorphos of the half-ton impactor (which takes nothing on board, except a solar sensor, a star tracker and a camera to support navigation when launching against the center of the small asteroid) at a speed of 6 km / s produce a change in system speed of 0.4 mm / s.
It may seem little, but the effect is cumulative. The expected result is that the impact changes the speed of Dimorphos’ orbit by about half a millimeter per second, resulting in a 10-minute orbital period change.
Still with 11 million kilometers between us and the system, the cumulative change in the trajectory would surely remove the collision with our planet – and that certainty would be assured by Hera, which will follow the system for the remaining years until it arrives in our neighborhood.
Other probes followed asteroids and are returning to Earth with samples. Japan’s Hayabusa2, launched in 2018 to study the asteroid Ryugu, will land in Australia on December 6. In the same year, OSIRIS-REx went up into space, only to arrive on Earth in 2023 with data on the asteroid Bennu.