Nasa's Dart mission successfully changes asteroid's orbit

A spacecraft that ploughed into a small, harmless asteroid millions of kilometres away succeeded in shifting its orbit, Nasa said on Tuesday in announcing the results of its save-the-world test.

The space agency attempted the first test of its kind two weeks ago to see if in the future a killer rock could be nudged out of Earth's way.

"This mission shows that Nasa is trying to be ready for whatever the universe throws at us," Nasa Administrator Bill Nelson said during a briefing at Nasa headquarters in Washington.

The Dart spacecraft carved a crater into the asteroid Dimorphos on September 26, hurling debris out into space and creating a cometlike trail of dust and rubble stretching several thousand kilometres. It took days of telescope observations from Chile and South Africa to determine how much the impact altered the path of the 160-metre asteroid around its companion, a much bigger space rock.

Before the impact, the moonlet took 11 hours and 55 minutes to circle its parent asteroid. Scientists had hoped to shave off 10 minutes but Nasa administrator Bill Nelson said the impact altered the asteroid's orbit by about 32 minutes.

"This mission shows that Nasa is trying to be ready for whatever the universe throws at us," Nelson said during a briefing at Nasa headquarters in Washington.

Neither asteroid posed a threat to Earth — and still don't as they continue their journey around the sun. That's why scientists picked the pair for the world's first attempt to alter the position of a celestial body.

A plume of dust and debris blasted from the surface of the asteroid Dimorphos by Nasa's DART spacecraft after it impacted on September 26. Photo / Nasa via AP

"We've been imagining this for years and to have it finally be real is really quite a thrill," said Nasa program scientist Tom Statler.

Launched last year, the vending machine-size Dart — short for Double Asteroid Redirection Test — was destroyed when it slammed into the asteroid 11 million kilometres away at 22,500km/h.

Johns Hopkins University's Applied Physics Laboratory in Maryland built the spacecraft and managed the US$325 million mission.

"This is a very exciting and promising result for planetary defense," said the lab's Nancy Chabot.