The Dart mission (Dart, in English) took off in November from California. After ten months of travel, the spacecraft should hit the asteroid Demorphos at 23:14 GMT on Monday (1:14 a.m. Tuesday in France), at a speed of more than 20,000 kilometers per hour. The ship is no larger than a car and is about 160 meters in diameter (half the height of the Eiffel Tower). Do not panic, Demorphos does not pose a threat to the Earth in any way: its orbit around the Sun passes only seven million kilometers from us at its closest point.
But the mission is “important to complete it before we discover a real need,” said Andrea Riley, NASA’s mission manager. The moment of impact promises to be amazing. It’s not a matter of destroying the asteroid but of pushing it up a bit. This technique is called the kinetic effect. Demorphos is actually a satellite of a larger asteroid, Didymus (780 meters in diameter), orbiting in 11 hours 55 minutes. The goal is to reduce Demorphos’ orbit around Didymus by about ten minutes.
This change can be measured with telescopes from Earth. The goal may seem modest, but this presentation is important for the future. The goal is to better understand how Demorphos, which represents a group of fairly common asteroids, the exact composition of which is unknown, interacts. The effect of the impact will largely depend on its porosity, that is, whether it is somewhat compacted.
one frame per second
To hit such a small target, the ship will steer independently for the past four hours, like a self-guided missile. His camera, called Draco, will take the first pictures of the asteroid at the last minute, its shape not yet known (round, rectangular, etc.). At a rate of one frame per second, it can be seen directly on Earth with a delay of only about 45 seconds.
“It’s going to start out as a small point of light, until it fills the entire frame,” said Nancy Chabot, of the Applied Physics Laboratory (APL) at Johns Hopkins University, where the control center is located. “These images will continue to appear until this does not happen,” she added, referring to the moment of the explosion. Three minutes later, a shoebox-sized satellite, called LICIACube launched by the craft a few days ago, will pass about 55 kilometers from the asteroid to capture images of the ejecta. They will be brought back to Earth in the following weeks and months.
The event will also be monitored by the Hubble and James Webb telescopes, which should be able to detect a bright cloud of dust. Then the European Hera probe, scheduled to launch in 2024, will closely monitor Demorphos in 2026 to assess the consequences of the collision and calculate the mass of the asteroid for the first time.
Very few known asteroids are considered dangerous, and none for the next 100 years. “But I guarantee that if you wait too long, there will be some object,” said Thomas Zurbuchen, NASA’s chief scientist. Almost 30,000 asteroids of all sizes have been cataloged near Earth (they are called near-Earth objects, that is, their orbit intersects with our planet). About 3,000 new species are found each year.