A Nasa spacecraft ready to crash into an asteroid to deflect its trajectory.
Steph Deschamps / September 23, 2022
A mission worthy of a science fiction movie. NASA will attempt, for the first time in the world, to divert the trajectory of an asteroid by projecting a kamikaze ship onto it. A test of "planetary defense", which must allow to better protect humanity against a possible future threat. The Dart mission took off in November from California. After ten months of travel, the spacecraft is scheduled to hit the asteroid Dimorphos at 23:14 GMT on Monday, September 26 (01:14 French time), at a speed of over 20,000 km / h.
The spacecraft is no bigger than a car, and its target is about 160 meters in diameter (half the height of the Eiffel Tower). Dimorphos is in no way a threat to the Earth: its orbit around the Sun passes only seven million kilometers from us at its closest. But the mission "is important to achieve before we discover a real need", said Andrea Riley, in charge of the mission at Nasa.
The moment of the impact promises to be spectacular and can be followed live on the American agency's video channel. It is not a question of destroying the asteroid, but of pushing it slightly, a technique known as kinetic impact. Dimorphos is actually the satellite of a larger asteroid, Didymos (780 meters in diameter), which it circles in 11 hours and 55 minutes. The goal is to reduce the orbit of Dimorphos around Didymos by about ten minutes. This will allow a better understanding of how Dimorphos will react, representative of a fairly common asteroid population, but whose exact composition is not known. The effect of the impact will depend largely on its porosity, i.e. whether it is more or less compact.
To reach such a small target, the spacecraft will navigate autonomously during the last four hours, like a self-guided missile. Its camera, called Draco, will take at the last moment the very first images of the asteroid, whose shape is not yet known (round, oblong...). Three minutes after the impact, a satellite the size of a shoebox, called LICIACube and released by the spacecraft a few days ago, will pass at about 55 km from the asteroid to capture images of the ejecta. They will be sent back to Earth in the following weeks and months.
If Dart misses its target, the spacecraft should have enough fuel for another attempt in two years. And if the mission succeeds, it will be a first step toward a true defense capability, according to Nancy Chabo of the Applied Physics Laboratory (APL) at Johns Hopkins University, where the control center is located. "The Earth has been hit by asteroids for billions of years, and it will happen again." For now, very few of the known asteroids are considered potentially dangerous, and none are over the next 100 years.