Science fiction films such as “Armageddon” or more recently “Don’t Look Up: Cosmic Denial” have long dealt with deflecting the trajectory of an asteroid by projecting a kamikaze ship. This time, NASA will finally attempt what has never been done before, a test of “planetary defense” designed to better protect humanity from a possible future threat.
The dart mission – in German dart – started in November in California. After a ten-month journey, the ship is scheduled to hit the asteroid Dimorphos at 1:14 a.m. on Tuesday at a speed of more than 20,000 km/h. The ship is no bigger than a car and its destination is about 160 meters in diameter, half the height of the Eiffel Tower.
press it lightly
Don’t panic, Dimorphos poses no threat to Earth in any way. Its orbit around the Sun is only seven million kilometers from us at its closest. But the mission “is important before we see a real need,” estimates Andrea Riley, NASA’s mission manager.
The moment of impact promises to be spectacular and can be followed live on the American agency’s YouTube channel. It won’t be about destroying the asteroid, it’s about pushing it slightly. The technique is called kinetic impact.
Dimorphos is actually the satellite of a larger asteroid, Didymos – with a diameter of 780 meters, which it orbits in 11 hours and 55 minutes. The aim is to shorten the orbit of Dimorphos around Didymos by about ten minutes.
This change can be measured with telescopes from Earth by observing the variation in brightness as the small asteroid passes in front of the large one. The goal may seem modest, but this demonstration is crucial for the future.
The goal is to better understand how Dimorphos, representative of a population of fairly common asteroids whose exact composition is unknown, will react. The impact of the impact depends largely on its porosity, ie whether it is more or less compact.
In order to hit such a small target, the ship steers autonomously for the last four hours, like a self-guided rocket. His camera, named Draco, will take the very first pictures of the asteroid, whose exact shape is not yet known, at the last moment. At a rate of one frame per second, they will be visible live on Earth with a delay of only about 45 seconds.
“It will start with a small point of light until it fills the entire image,” says Nancy Chabot of the Applied Physics Laboratory (APL) at Johns Hopkins University, where the control center is located. These images will continue to arrive until they stop arriving,” at the time of the explosion.
Three minutes later, a shoebox-sized satellite called LICIACube, released from the spacecraft a few days ago, will fly by about 55 km from the asteroid to capture images of the ejecta. They will be sent back to Earth over the coming weeks and months.
The event is also being observed by the Hubble and James Webb Space Telescopes, which should be able to spot a bright dust cloud. Then the European Hera probe, due to launch in 2024, will closely observe Dimorphos in 2026 to assess the impact’s consequences and calculate the asteroid’s mass for the first time.
A first step
Very few of the known asteroids are considered potentially dangerous, and none will be for the next 100 years. But “I guarantee you that if you wait long enough, there will be an object,” says Thomas Zurbuchen, NASA’s chief scientist.
Nearly 30,000 asteroids of all sizes have been cataloged near Earth. They are called near-Earth objects, which means that their orbit crosses that of our planet. About 3000 new ones are found every year.
Almost all of the animals have been sighted from a kilometer or more, according to the scientists. They estimate they only know about 40% of asteroids that are 140 meters and larger – those that can devastate an entire region.
If Dart misses its target, the ship should have enough fuel for another attempt in two years. And if the mission is successful, according to Nancy Chabot, it will be a first step toward real defensive capability.
And finally: “Earth has been hit by asteroids for billions of years, and it will happen again. Let’s make sure as humans that we live in a civilization where we can avoid that.”
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