DART's mission is important because there may be other space rocks of the same size on a collision course with our planet.

DART smashed into the asteroid moonlet Dimorphos on Monday in order to demonstrate the strategy of planetary defense. There was a lot of speculation on the internet that NASA might have sent a harmless space rock towards Earth.

It's groundless to speculate about such things. There is no way that DART's death dive could change the position of Dimorphos and Didymos around the sun. The moonlet Dimorphos is around the Didymos, which is 2,560 feet wide. Scientists say that the Didymos system is like a security brake against unwanted alterations.

The big guy is more important than the little guy. The DART mission for NASA is being held back by something, according to the chief scientist for planetary defense at the APL. It's difficult to measure the change in the sun's position around the system.

How big is a space rock?

The Didymos system is not a concern for planetary defense experts.

The Didymos system is still several million miles away from Earth. Tom Statler, a NASA planetary scientist, told a news conference that it was not a threat. It won't make it a threat in our lifetimes.

Astronomers model asteroids for a long time. Due to the pull of the giant planets of the solar system, the orbits shifts. One day, an asteroid that is currently of no concern may become a threat.

We don't know much about the risk of asteroids. According to NASA and its partners, only about 40% of asteroids larger than 480 feet are known. Even though there are no known asteroids that pose a threat to Earth in the foreseeable future, space agencies around the world want to know how to avoid such a space rock. The DART mission is the reason.

An artists impression of the DART probe smashing into the asteroid Dimorphos.

An artists impression of the DART probe smashing into the asteroid Dimorphos. (Image credit: ESA–ScienceOffice.org)

How much damage would an asteroid the size of Dimorphos cause if it were to hit Earth?

The non-avian dinosaurs went extinct after an impact of an asteroid some 10 kilometers wide. The region where a Dimorphos-sized rock crashed down would be destroyed.

If an asteroid as big as Dimorphos fell on the city of London, windows would break over the whole southeast of England, and the damage in the Greater London area would be very extreme. There would be no survivors in the center of London because of the impact and air blast.

The impact of such an asteroid would cause a crater over 1 mile wide and over 1,200 feet deep, which would knock down buildings hundreds of miles away.

Collins and his colleagues created an online tool that allows researchers and members of the public to explore impacts of asteroids of different sizes. If it happened deep in the ocean, the waves would move to the low-amplitude waves before they reached the coast.

The impact of a rock falling into the ocean would be terrible. Even though the chances of an asteroid hitting a major city is low, planet defenders want to have technology ready to protect them.

How will DART help us protect against other space rocks?

A planetary defense mission would only be able to get it right if there were many asteroids. The data from the DART mission will be useful for any future campaign.

There is a huge data-gathering effort going on. There are hundreds of ground-based and space-based telescopes, as well as a little cubesat called LICIA that traveled to the Didymos system with DART but was released two weeks ago to take images of the impact and its aftermath.

The European Space Agency will launch the Hera mission in 2024, which will make additional measurements of Didymos and Dimorphos to learn more about the asteroids and their mechanics. Scientists and engineers will be able to calculate the behavior of other asteroids using this data and one day design a real deflection mission with the best chance of success.

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