Watch: Nasa's DART spacecraft strikes asteroid in key test of planetary defence

On Monday, a Nasa spaceship struck an asteroid seven million miles away in order to deflect its orbit, succeeding in a historic test of humanity's ability to prevent a celestial object from devastating life on Earth.

The Double Asteroid Redirection Test (DART) impactor hit its target, the space rock Dimorphos, at 7.14pm Eastern Time (23.14 GMT), 10 months after blasting off from California on its pioneering mission.

"We're embarking on a new era, an era in which we potentially have the capability to protect ourselves from something like a dangerous hazardous asteroid impact," said Lori Glaze, director of Nasa's planetary science division.

Dimorphos — a 160m asteroid roughly comparable in size to an Egyptian pyramid — orbits a half-mile long big brother called Didymos. Never seen before, the "moonlet" appeared as a speck of light around an hour before the collision.

Its egg-like shape and craggy, boulder-dotted surface finally came into clear view in the last few minutes, as DART raced toward it at roughly 23,500km/h.

Nasa scientists and engineers erupted in applause when the screen froze on a final image, indicating that signal had been lost and the impact had taken place.

To be sure, the pair of asteroids pose no threat to our planet, as they loop the Sun every two years.

Yet, Nasa has deemed the experiment important to carry out before an actual need is discovered.

By striking Dimorphos head on, Nasa hopes to push it into a smaller orbit, shaving 10 minutes off the time it takes to encircle Didymos, which is currently 11 hours and 55 minutes.

Ground telescopes — which can't see the asteroid system directly, but can detect a shift in patterns of light coming from it — should provide a definitive orbital period in the coming days and weeks.

The proof-of-concept has made a reality of what has before only been attempted in science fiction — notably in films such as Armageddon and Don't Look Up.

Minutes after impact, a toaster-sized satellite called LICIACube, which already separated from DART a few weeks ago, was expected to make a close pass of the site to capture images of the collision and the ejecta — the pulverised rock thrown off by the strike.

LICIACube's pictures will be sent back in the next weeks and months.

Also watching the event are an array of telescopes, both on Earth and in space — including the recently operational James Webb — which might be able to see a brightening cloud of dust.

The mission has set the global astronomy community abuzz, with more than three dozen ground telescopes participating, including optical, radio and radar.

"There's a lot of them, and it's incredibly exciting to have lost count," said DART mission planetary astronomer Christina Thomas.

Finally, a full picture of what the system looks like will be revealed when a European Space Agency mission four years down the line, called Hera, arrives to survey Dimorphos' surface and measure its mass, which scientists can currently only guess at.

Very few of the billions of asteroids and comets in our solar system are considered potentially hazardous to our planet, and none are expected in the next hundred years or so.