How a group of amateur astronomers captured a NASA spacecraft crashing into an asteroid

Last year’s DART mission to explore whether a spacecraft could be used to divert an incoming asteroid has produced a collection of interesting research papers, including one that explores the crucial role of citizen scientists.

Last September, the world watched in delight as NASA deliberately crashed a spacecraft into an asteroid in a test of planetary defense. The idea of the DART mission was to see whether an impact from a spacecraft could change the trajectory of an incoming asteroid in case such a looming disaster ever threatened the Earth. 

The impact and its aftermath were observed by telescopes all across the planet and by several in space, including the Hubble and James Webb Space Telescopes, and preliminary data showed that the test had been successful in changing the orbit of this asteroid. Then scientists got to work analyzing all the data they had collected for more insights.

This week, five new papers in the journal Nature reveal more about what happened when the spacecraft impacted the asteroid and how effective this method would be at deflecting an asteroid that really threatened Earth. Although four of these papers are based on data from big professional telescopes, the fifth is unusual as it uses data from citizen scientists — amateur astronomers who worked together to observe the impact using small backyard telescopes.

Space telescopes like Hubble and JWST were able to see the effects of the impact in great detail, but they missed the impact itself by just a few minutes. That’s because these telescopes are highly sensitive and can observe very distant targets, but it’s hard to move them into the exact right position to catch a relatively close and very fast-moving object like an asteroid in our solar system.

So it was on ground-based telescopes to capture as much data as they could of the entire impact event. But it wasn’t easy to get a good viewing spot. “At the time of the impact, there weren’t a lot of places on Earth where you could observe Didymos, the asteroid,” Ariel Graykowski of the SETI Institute, lead author of the citizen science paper, tells The Verge. “There were only a few places in Africa which had good visibility.”

Having a network of telescopes across the world made it possible to get observations from these locations, such as Nairobi in Kenya and Réunion Island in the Indian Ocean. Graykowski works with the Unistellar telescope network to get data from both individual telescope users and science outreach groups like the Traveling Telescope project, which promotes science education around Kenya and which organized a special observation event in Nairobi for the DART impact.

“Because we have this network, we could see the impact,” Graykowski said, as the network captured both the initial brightening caused by the impact and the subsequent cloud of material, called ejecta, which was thrown up when the spacecraft struck the asteroid. “So the citizen science was a very necessary tool.”

The data collected by the network was able to measure the mass of the ejecta, or how much material was displaced by the impact. By combining that with data on the speed of the ejecta, scientists can calculate how much energy was transferred into the asteroid — and that shows how effective the “crash a spacecraft into an asteroid to knock it off course” method is for planetary defense. 

Another interesting oddity detected by the citizen science network was a change in color, with a mysterious reddening observed just as the impact happened. A similar effect had been seen in a previous asteroid impact mission called Deep Impact in 2005, which was thought to be due to optical effects of the cloud of dust being thrown up. 

“So that wasn’t just a fluke in the Deep Impact mission — we see it here too,” Graykowski said. Now the question is whether this reddening is in fact an optical effect or whether it could be due to the composition of the asteroid’s surface. “And that would be really cool if it was because that tells us about the material that makes up the asteroids, at least on their surfaces. And the asteroids are some of the oldest bodies in the solar system.”

One of the great advantages of a citizen science network is that it can be used for continuous, ongoing observations. Major telescopes are oversubscribed, meaning more researchers want time on them than can be accommodated, so it’s both hard to get observing time and extremely difficult to observe an event right as it happens. But with a network, there’s always someone watching. 

“The most exciting thing is when something falls apart in the sky or something explodes in the sky,” Graykowski said. “We want to know why that happened, and the best way to know is to capture it when it happens. So [the network] has been a really cool tool because we’ve caught things we never would have been able to capture before.”