Much more than large potentially dangerous pebbles, asteroids are small varied geological worlds that tell the origins of the Solar System, but are still little known: it is to explore this “unknown land” that the HERA probe will take off, in the wake. of DART.
From the night of Monday to Tuesday, NASA’s DART mission will have December the trajectory of an astéroïde in percutant Dimorphos, a small “lune” which tourne autour d’an astéroïde plus gros, Didymos, located at 11 million kilometers from the earth. This life-size experiment aims to reduce the duration of the orbit of the small asteroid around the larger one, to find out if humanity is capable of voluntarily modifying the trajectory of an asteroid that threatens our planet.
“Such a system of two asteroids is a perfect testbed for a planetary defense experiment, but it is also a completely new environment,” said Ian Carnelli, manager of the European Space Agency’s (ESA) HERA mission.
Named HERA in honor of the Greek goddess of marriage, the European probe will take off in October 2024, arriving in 2026 at Dimorphos. Objective: return to the “crime scene” to assess the consequences of the DART impact.
The deviation test will thus be fully documented, thanks to the information collected by the HERA instruments (cameras, lasers, high resolution imagers, radar, etc.). This will allow planetary defense experts to reliably feed models to extrapolate impact scenarios.
“A new world”
“We need to know the nature and composition of asteroids because, depending on the texture of the rock, they do not represent the same danger,” said Bhavya Lal, associate administrator of NASA, during the International Astronautical Congress this week in Paris.
Scientists hope to be surprised by the results of the investigations. Because “we ignore almost everything” about these celestial bodies, says Patrick Michel, principal investigator of HERA. “It is a new world that we are going to discover.”
For this astrophysicist, asteroids “are not just pebbles drilling in space, but fascinating and complex small geological worlds, with craters, basins, rock fields, particle ejections…”
But it is difficult for science to understand these territories because on their surface gravity is very weak compared to that of Earth: the behavior of matter there is “totally counterintuitive, we cannot rely on images to know how asteroids behave, also you have to touch them,” explains Patrick Michel.
An example? A small explosion near the surface of the asteroid Ryugu (discovered in 1999) formed a 15-meter crater, much larger than simulations predicted. And although the rock was supposed to be solid, “the surface behaved like a fluid on impact, isn’t that surprising?”
go back in time
Binary systems like Didymos and its satellite Dimorphos make up around 15% of known asteroids and have so far gone unexplored.
At 160 meters in diameter (the size of the Great Pyramid of Giza), Dimorphos will also be the smallest asteroid ever studied.
Shape, mass, chemical composition, internal structure, impact resistance, shape of the crater caused by DART: HERA’s instruments should reveal the secrets of Dimorphos. At the end of the mission, a microsatellite will even land on its surface to measure how it bounces back.
This unpublished documentation will also help astrophysicists to go back in time, since asteroids are excellent “tracers of the history of the Solar System”, says Patrick Michel. These small rocky bodies have kept in themselves the memory of the composition of the system and its planets, which were formed by collisions.
“Today, we are in an era where all solid surfaces in the Solar System are cratered. To find the original scenario, we need to understand what happens when two bodies collide.” Not in the laboratory, but on a real scale thanks to the DART-HERA couple, scientists hope.