The asteroid NASA smacked around last week now has a tail almost as long as the Earth is wide.

The Double Asteroid Redirection Test (DART) spacecraft successfully slammed into Dimorphos, a moon asteroid orbiting the larger Didymos, on September 26. It was a test to see whether deflecting an incoming asteroid could one day save humanity from going the way of the dinosaurs.

Two days after the collision, astronomers pointed the Southern Astrophysical Research (SOAR) Telescope in Chile at the binary system, capturing a “vast plume of dust and debris”, the US National Science Foundation said this week.

“It is amazing how clearly we were able to capture the structure and extent of the aftermath in the days following the impact,” said Teddy Kareta of Lowell Observatory in Arizona.

It’s about 10,000km long – and could cover Russia from end to end. Dimorphus itself is about 170m across.

“Now begins the next phase of work for the DART team as they analyze their data and observations by our team and other observers around the world who shared in studying this exciting event,” added Matthew Knight of the US Naval Academy. 

“We plan to use SOAR to monitor the ejecta in the coming weeks and months.”

It’s not clear yet whether the deflection worked to move Dimorphos and Didymos’ orbit. Neither pose a threat to Earth – at least, they didn’t before the collision. Presumably that’s still the case…

Either way, we’ll hopefully know soon. If it’s only a subtle change, we might have to wait until 2024, when European spacecraft Hera will retrace its steps

Any change to its path is expected to be small, but will build up over time.

“If you were going to do this for planetary defence, you would do it five, 10, 15, 20 years in advance in order for this technique to work,”  Nancy Chabot of Johns Hopkins University’s Applied Physics Laboratory said in September.