A Nasa spacecraft has smashed into an asteroid at 23,000kph, in a spectacular first test of deflection technology that could in future change the path of an incoming space rock to prevent a cataclysmic collision with Earth.
As the 600kg Dart projectile closed in on its target, Dimorphos, early on Tuesday UK time, its camera sent back a spectacular series of images — one per second — until individual rocks, boulders and smooth ground became visible on the surface of the peanut-shaped asteroid.
Then came the moment of impact, right on target, and the picture feed died. Scientists and engineers at mission headquarters at Johns Hopkins University Applied Physics Laboratory in the US erupted in the cheers and applause, hugs and handshakes that traditionally greet a successful space mission.
“We are now embarking on a new era for humankind — an era in which we potentially have the ability to protect ourselves from a hazardous asteroid impact,” said Lori Glaze, Nasa planetary science director, immediately after impact.
“Now is when the science really starts,” Glaze added. “Now that we have impacted, we’re going to see how effective we’ve been [at deflecting the asteroid].”
The collision was observed by LiciaCube, a small satellite made in Italy which had accompanied Dart on its journey to Dimorphos 11mn km from Earth. It separated from its parent spacecraft 15 days ago and flew past the asteroid a few minutes after the impact, at a safe distance of 55km.
LiciaCube will take longer to transmit its images back on Earth for scientific analysis. They are expected to show not only the impact site but also the resulting cloud of dust and gas, giving Dimorphos a temporary tail like a miniature comet.
But terrestrial telescopes will carry out the main job of assessing the effects of the collision over the next few weeks. The asteroid, which is about 160 metres in diameter, is too far from Earth for them to glean images in detail but they will be able to see the initial dust plume and later assess how much the impact has shifted its path through space.
Nasa chose this target because it is part of an unusual double asteroid. Dimorphos moves like a moonlet around a larger partner called Didymos — and a deflection in this local orbit is far easier to detect than a change of orbit around the sun would be.
Dimorphos takes about 11 hours to travel around Didymos. Advance calculations suggest that the impact will cut this time by 10 to 15 minutes.
The actual decrease in its orbital time will provide key information about the asteroid’s texture — hard or soft, consolidated or crumbly.
There is zero chance that the impact could push the asteroid on to a path that threatens Earth, astronomers say.
In 2024 the European Space Agency will launch a probe called Hera to carry out a detailed post-impact survey of the binary asteroid system in 2026.
The Dart mission is the first attempt by humanity to alter the trajectory of a natural object in space. “We’ve all seen it on movies like Armageddon, but the real-life stakes are high,” said Bill Nelson, Nasa administrator.
Surveys of space have convinced astronomers that there is no risk over the next few centuries of Earth encountering anything as big as the 10km-wide asteroid that hit 66mn years ago and put an end to the dinosaurs. But there are thousands of smaller “near-Earth objects” that are still uncharted — and capable of devastating vast regions of the planet.
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