a NASA spacecraft prepares to deflect an asteroid

Spaceships are not normally designed to crash. Yet this is exactly what NASA was preparing to do on Monday night, by deliberately projecting a machine onto an asteroid to throw it off course. An unprecedented mission that should allow us to learn how to protect humanity against a possible future threat.

The target asteroid poses no danger. But the mission, called Dart, should “help determine our response if we detect an asteroid threatening to hit Earth” in the future, NASA chief Bill Nelson said Monday.

The moment of impact, 11 million kilometers from us, can be followed live on NASA’s video channel.

The ship, no bigger than a car, took off in November from California. After ten months of travel, she must reach her goal at 23:14 GMT on Monday, at a speed of over 20,000 km / h.

“We are changing the motion of a natural celestial body in space, humanity has never done this before,” said Tom Statler, chief scientist for the mission. “It’s something out of science fiction books and Star Trek episodes when he was a kid. And now it’s real.”

The target is actually a pair of asteroids: a large one, Didymos (780 meters in diameter), and its satellite, Dimorphos (160 meters in diameter), in orbit around it. The two are only a kilometer apart.

It is in the little one, Dimorphos, that the ship must crash. This asteroid currently revolves around the larger one in 11 hours and 55 minutes, and the goal is to reduce its orbit by about 10 minutes.

The change can be measured with telescopes on Earth, by observing the change in brightness as the small asteroid passes in front of the large one.

When will we know if it worked? “I’d be surprised if we had a firm measure of change in less than a few days, and I’d be surprised if it took more than three weeks,” said Tom Statler.

– Integrated camera –

Meanwhile, on Monday, the ship’s onboard camera, called Draco, will take one picture per second. They will arrive at Earth with a delay of only about 45 seconds.

To hit such a small target, the spacecraft will steer autonomously for the last four hours, like a self-guided missile.

It will target Didymos first, before Dimorphos appears.

The tiny asteroid, which has never been imaged before, will initially be no larger than one pixel, before filling the entire frame, until radio silence sets in after the explosion.

The approximately forty people present in the control room of the Applied Physics Laboratory (APL) at Johns Hopkins University in Maryland will be ready to intervene if necessary.

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

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

– Unknown –

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. The porosity 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,” Tom Statler warned.

None of the known asteroids threaten Earth for the next 100 years.

Nearly 30,000 asteroids of all sizes have been cataloged in its vicinity (they are called near-Earth cruisers, that is, their orbit crosses that of our planet).

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 have to figure out the best way to defend against them.

But the Dart mission is a crucial first step, Mr Johnson said: “It’s a very exciting time … in the history of space, and even in the history of mankind.”


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