A spacecraft launched to test technology that could tip an asteroid off course.

Nasa’s Dart mission aims to determine how difficult it would to stop a large space rock colliding with Earth.

To test how fast and how far the spacecraft can alter its path, it will collide with Dimorphos.

A few hundred metre-thick chunks of cosmic debris could collide with the planet and cause destruction across continents.

At 06:20 GMT, a Falcon 9 rocket carrying Dart’s spacecraft launched from Vandenberg Space Force Base, California.

This is the first attempt at deflecting an asteroid in the interest of protecting Earth. However, this particular asteroid does not pose any threat.

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“Dart will only change the period of Dimorphos’ orbit by a small amount. That’s really all you need in the case that an asteroid’s discovery is made well in advance,” Kelly Fast, from Nasa’s planetary defense coordination office, said.

She commented on the launch by saying: “We are not yet out of the woods. We have to get out Dimorphos. But this is a big step along the path.”

Asteroids are the leftover building blocks of our Solar System. A collision can occur in the rare case that a space rock’s path through the Sun intersects that of Earth, so that they are not both at the same moment.

The Dart mission, which will cost $325m (PS240m), will aim at a pair of asteroids orbiting each other. This is known as a binary. Didymos is the larger object, measuring around 780m in diameter, and Dimorphos, its smaller companion, around 160m in width.

Dimorphos-sized objects could explode with many times as much energy as a standard nuclear bomb, causing widespread destruction and thousands of deaths. Asteroids larger than 300m in diameter could destroy entire continents, while ones larger than 1km would have global effects.

Dart will orbit the Sun after it has escaped Earth’s gravity. The binary will be intercepted by Dart as it approaches Earth’s 6.7 million mile mark in September 2022.

Dart will hit the moonlet Dimorphos at around 15,000mph (6.6 km/s). This will change the object’s speed by just a fraction of millimetre per sec, which in turn will alter Didymos’ orbit. Although it is a small shift, it may be enough to cause an object to collide with Earth.

“There are many more small asteroids that there are large ones, so the most likely threat we ever face – if ever we have to face one- is going to be from anasteroid around these size,” stated Tom Statler at Nasa.

Congress gave Nasa the mandate to track 90% of all near-Earth asteroids greater than 140m (460ft) in 2005. This category does not pose a threat to Earth. However, only 40% of the objects have been discovered.

Dart is carrying Draco, a camera that captures images of both asteroids. This will help the spacecraft to point in the right direction for Dimorphos to collide.

The American spacecraft will launch a small, Italian-built satellite named LiciaCube about 10 days before Dart reaches its target. Images of the impact and debris plume, as well as the resulting crater will be sent back by the smaller craft.

Telescopes on Earth will measure the tiny deviation in Dimorphos’ path around Didymos. Tom Statler stated: “What we really want is to know: Did we really deflect an asteroid? And how efficient was it done?”

A binary is the ideal laboratory for such tests. The impact should alter Dimorphos orbit around Didymos approximately 1%. This change can be detected using ground telescopes within weeks or months.

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  • But, Dart would hit a single asteroid and its orbital period around Sun would change by approximately 0.000006%. This would take many years for us to determine.
  • It is so tiny that even the best telescopes can’t see it. Dimorphos blocks some Didymos’ reflection light when it passes in front of Didymos, but the reverse happens when Didymos moves behind its smaller companion.
  • Andy Rivkin, Dart’s investigator lead, stated that “we can measure the frequency these dimmings,” adding, “That’s how it’s possible to know that Dimorphos travels around Didymos for a period of 11 hour, 55 minutes.”
  • Astronomers will again take these measurements after the impact. “They’ll occur a little more often – maybe it will be two every 11 hour 45 minutes, or maybe it’ll just be 11 hours, 15 minutes,” Dr Rivkin said. He is based at Johns Hopkins University Applied Physics Laboratory in Laurel (Maryland).
  • Because of its inextricable interior structure, there is some uncertainty about how Dimorphos will react to the impact. It might produce lots more debris if Dimorphos has a solid interior, and not a lot of space.
  • The kinetic impactor technique is Dart’s method of dealing with hazardous asteroid. There are many other options, such as moving an asteroid slowly and detonating nuclear bombs – a technique that is familiar to Hollywood moviegoers like Deep Impact and Armageddon.