NASA spacecraft hits an asteroid to deflect it, for the first time

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NASA’s “Dart” mission is a success: on Monday night, a spacecraft deliberately hit the asteroid Dimorphos, located about 11 million kilometers from Earth, to divert its trajectory and thus train in case another asteroid one day threatens to destroy humanity.

Confirmed impact: A NASA spacecraft deliberately crashed on an asteroid on Monday, September 26, to divert its trajectory, during an unprecedented test mission that should allow humanity to learn how to protect itself from a possible future threat.

The ship, smaller than a car, rushed at a speed of more than 20,000 km / h on its target, reached at the scheduled time (23:14 GMT). The NASA teams, gathered at the mission control center in Maryland, United States, exploded with joy at the moment of the crash.

A few minutes earlier, the asteroid Dimorphos, located about 11 million kilometers from Earth, has grown little by little in the spectacular images broadcast live by the ship. We could clearly make out the pebbles on its gray surface, just before the images stopped at the moment of the explosion.

“We are embarking on a new era, where we potentially have the ability to protect ourselves from a dangerous asteroid impact,” said Lori Glaze, director of planetary sciences at NASA.

Dimorphos is about 160 meters in diameter and does not represent any danger to our planet. It is actually the satellite of a larger asteroid, Didymos, which has so far circumnavigated in 11 hours and 55 minutes. NASA seeks to reduce the orbit of Dimorphos in 10 minutes, that is, to bring it closer to Didymos.

“Planetary defense” mission

It will take a few days to a few weeks before scientists can confirm that the asteroid’s trajectory has been altered. They will do this thanks to telescopes on Earth, which will observe the variation in brightness as the small asteroid passes in front of and behind the large one.

If the goal remains modest compared to the disaster scenarios in science fiction movies like “Armageddon,” this “planetary defense” mission, dubbed Dart, is the first to test such a technique. It allows NASA to train in case an asteroid threatens to hit Earth one day.

The ship had traveled for ten months since taking off in California. To hit a target as small as Dimorphos, the last phase of the flight was fully automated, like a homing missile.

Three minutes after impact, a shoebox-sized satellite, called LICIACube and launched by the spacecraft upriver, was expected to pass within about 55 km of the asteroid to capture images of the ejection.

close scrutiny

The event was also to be observed by the Hubble and James Webb Space Telescopes, which should be able to detect a bright cloud of dust and thus help assess the amount of material ejected.

All of this should allow a better understanding of the composition of Dimorphos, representative of a population of fairly common asteroids, and therefore measure the exact effect that this technique, called kinetic impact, can have on them.

The European probe Hera, which will take off in 2024, will also closely observe Dimorphos in 2026 to assess the consequences of the impact and calculate, for the first time, the mass of the asteroid.


Asteroids have held surprises for scientists in the past. In 2020, the US Osiris-Rex probe had sunk much deeper than expected to the surface of the asteroid Bennu. Likewise, the composition of Dimorphos is currently unknown.

“If the asteroid responds to the Dart impact in a totally unexpected way, it could actually lead us to reconsider the extent to which kinetic impact is a generalizable technique,” chief scientist Tom Statler of the mission warned last week.

66 million years ago, the dinosaurs disappeared after the collision of an asteroid about 10 kilometers with the Earth.

About 30,000 asteroids of all sizes have been cataloged in the vicinity of the Earth (they are called near-Earth objects, that is, their orbit crosses that of our planet). Today, none of these known asteroids threaten our planet for the next 100 years. Except they’re not all on the list yet.

Those of a kilometer or more have been sighted almost all, according to scientists. But they estimate that they only know about 40% of the asteroids that measure 140 meters or more, those capable of devastating an entire region.

“Our most important job is to find” the missing, said Lindley Johnson, NASA’s planetary defense officer. The earlier they are detected, the more time experts will have to put in place a means of defending against them. The Dart mission is a crucial first step in this direction, according to him: “It is a very exciting period (…) for the history of space, and even for the history of mankind.”

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