Asteroids form small and diverse geological worlds that tell a lot about the way the solar system was formed, but information about them is still limited to this day… The Hera probe will be launched to discover these “unknown worlds” after the mission of the “Dart” spacecraft launched by NASA on Monday. .
On Monday night – Tuesday, NASA’s DART mission will attempt to divert an asteroid’s path by deliberately colliding with Demorphos, a small moon orbiting the larger asteroid Didymos 11 million kilometers from Earth.
This experiment aims to reduce the duration of the orbit of a small asteroid around a larger asteroid, to see if humans are able to modify the course of any asteroid that threatens Earth.
“A similar system of two asteroids represents an ideal test for an experiment aimed at defending life on Earth, and also constitutes a completely new environment,” said Ian Carnell, the responsible for the “HERA” mission at the European Space Agency.
The European Hera probe, named after the Greek goddess of marriage, Hera, is scheduled to be launched in October 2024 and will reach Demorphos in 2026. The purpose of this probe is to preview the results of the DART mission.
The asteroid diversion test will be fully documented thanks to the information collected by the “HERA” instruments (cameras, lasers, high-resolution imaging devices, radar…). This data will allow Earth-defense experts to reliably enhance the extrapolation models of impact scenarios.
“We need to know the nature of asteroids and their components, because the degree of risk varies for each of them according to the different types of rocks in them,” NASA Associate Administrator Bhavya Lal said during the International Astronautical Conference held this week in Paris.
Scientists expect to be surprised by the test results. Hera’s principal investigator, Patrick Michel, attributes this to “the ignorance surrounding everything” about these celestial bodies. “It’s a new world that we’re going to discover,” he says.
The astrophysicist considers asteroids “not just useless rocks in space, but rather amazing and complex small geological worlds, containing craters, rocky fields and shells of particles…”.
However, the scientific community finds it difficult to understand these places because the gravity on their surface is very weak compared to the Earth’s gravity, and thus the interaction of matter in them is “not intuitive at all, and we cannot rely on images to know how asteroids interact, so they should be reached as well,” explains Patrick. Michel.
For example, a small explosion near the surface of the asteroid Ryugu (discovered in 1999) created a 15-meter-deep crater, much larger than previously predicted by simulations. While the rocks were expected to be solid, “the surface reacted like a liquid when it exploded, isn’t that surprising?” says Michel.
Binary systems such as Didymos and its moon Demorphos represent about 15% of the known asteroids that have yet to be discovered.
With a diameter of 160 meters (the size of the largest pyramid among the Giza pyramids), Demorphos will be the smallest asteroid ever studied.
The instruments of the Hera probe are supposed to reveal the secrets surrounding Demorphos, from its shape, size, chemical composition, to its internal structure, the degree of its resistance to shocks, and the shape of the crater that the Dart spacecraft will create. At the end of the mission, a small satellite will land on its surface to monitor how it returns to its normal state.
This unparalleled documentation will help astrophysicists go back in time because asteroids are “excellent devices for revealing the history of the solar system,” according to Patrick Michel. These small, rocky bodies have preserved information about the composition of the system and its planets formed by collisions.
“We live today in an age when all the solid surfaces in the solar system contain craters,” says Michel. “To come up with a scenario for their formation, we need to understand what happens when two objects collide.” And we won’t come to this knowledge in the lab, but in fact thanks to the duo Dart and Hera, the scientists hope.