NASA: Probe impact on asteroid scattered 1,000 tons of rock across space

The NASA probe that deliberately hit an asteroid last September scattered a thousand tons of rock through space, which will help the American space agency with more information about the study of this type of material.

The main objective of the Dart mission (acronym for Double Asteroid Redirection Test) was to put into practice the first experiment to demonstrate a deflection technique, that is, the deflection of an asteroid to protect the planet.

Two asteroids that orbit the Sun and occasionally come close to Earth were NASA’s targets. They pose no threat to our planet, but their proximity has made them prime candidates for testing.

The larger of the two asteroids, Didymos, is 780 meters in diameter. Around it, orbits a smaller natural satellite, called Dimorphos—which was the object hit by the space probe.

Scientists working on the project were even able to assess the effectiveness of the impact. The force transferred to Dimorphos was 3.6 times greater than if the probe had simply been absorbed by the asteroid and produced no ejecta.

“If you blow the material a little off target, there will be a recoil force,” explained Andy Cheng, mission scientist and Johns Hopkins University Applied Physics Laboratory (JHU-APL).

“The result of that recoil force is that you put more momentum on the target and end up with a larger deflection.”

“If you’re trying to save Earth, that makes a big difference,” he said, as it would increase the time available to mount a defense or reduce the size of the projectile needed.

The Double Asteroid Redirection Test took place about 11 million km from Earth.

The NASA satellite, the size of a fridge, crashed at 22,000 km/h into the 160-metre-wide Dimorphos, destroying itself in the process.

Before impact, the time it took Dimorphos to orbit around the 780-meter-wide Didymos was 11 hours and 55 minutes.

Subsequent observations from the telescope indicated that this orbital period was reduced to 11 hours and 23 minutes — a change of 32 minutes.

“It was well worth the money,” said Andy Rivkin, leader of the Dart investigation team.

The 1,000 tonnes of space rock ejected, which he likened to “six boxcars of rock”, is only an initial estimate.

“The studies are still ongoing, it may be that this number is a minimum; it may be double that, it may even be 10 times more, according to some estimates.”

The ejected material is only a fraction of the total mass of Dimorphos, which is about 5 million tons.

However, the impact caused a big “mess”, and telescopes continue to monitor the debris moving away from the asteroid by tens of thousands of kilometers.

Studying the Didymos-Dimorphos system before and after the impact has revealed much about the properties of the two asteroids.

They are very similar to a type of meteorite that frequently falls to Earth called a common chondrite, said Cristina Thomas of Northern Arizona University.

US President Joe Biden has described the Dart mission as one of the US space agency’s three big successes in 2022. The other two are the recent Artemis-1 mission to the Moon and the first photos from the new James Webb Space Super Telescope.

Tom Statler, NASA Dart program scientist, agreed.

“The Dart has been a tremendous success. Of course, a successful mission doesn’t automatically guarantee that Earth is safe from anything that might come our way. But the Dart really is a giant step toward our goal of making the most avoidable asteroid impacts on Earth.”