Gigantic asteroids have smashed into the Earth before—RIP dinosaurs—and if we’re not watching out for all those errant space rocks, they could crash into our world again, with devastating consequences. That’s why Ed Lu and Danica Remy of the Asteroid Institute started a new project to track as many of them as possible.
Lu, a former NASA astronaut and executive director of the institute, led a team that developed a novel algorithm called THOR, which harnesses massive computing power to compare points of light seen in different images of the night sky, then matches them to piece together an individual asteroid’s path through the solar system. They’ve already discovered 104 asteroids with the system, according to an announcement they released on Tuesday.
While NASA, the European Space Agency, and other organizations have their own ongoing asteroid searches, all of them face the challenge of parsing telescope images with thousands or even 100,000 asteroids in them. Some of those telescopes don’t or can’t take multiple images of the same region on the same night, which makes it hard to tell if the same asteroid is appearing in multiple photos taken at different times. But THOR can make the connection between them.
“What’s magical about THOR is, it realizes that out of all those asteroids, this one in a certain image, and this one in another image four nights later, and this one seven nights later are all the same object and can be put together as the trajectory of a real asteroid,” Lu says. This makes it possible to track the object’s path as it moves, and to determine if it’s on a trajectory bound for Earth. Such a formidable task wouldn’t have been possible with older, slower computers, he adds. “This is showing the importance of computation in going forward in astronomy. What’s driving this is that computation is becoming so powerful and so cheap and ubiquitous.”
Astronomers typically spy asteroids with something called a “tracklet,” a vector measured from multiple images, typically taken within an hour. These often involve an observing pattern with six or more images, which researchers can use to reconstruct the asteroid’s route. But if the data is incomplete—say, because a cloudy night obstructs the telescope’s view—then that asteroid will remain unconfirmed, or at least untrackable. But that’s where THOR, which stands for Tracklet-less Heliocentric Orbit Recovery, comes in, making it possible to ascertain the path of an asteroid that would have otherwise been missed.
While NASA benefits from telescopes and surveys dedicated to spotting potentially hazardous asteroids, other data sets abound. And THOR can use almost any of them. “THOR makes any astronomical data set a data set where you can search for asteroids. That’s one of the coolest things about the algorithm,” says Joachim Moeyens, cocreator of THOR, and an Asteroid Institute fellow and graduate student at the University of Washington. For this initial demonstration, Moeyens, Lu, and their colleagues searched billions of images taken between 2012 and 2019 from telescopes managed by the National Optical Astronomy Observatory, many by a sensitive camera mounted on the Blanco 4-meter telescope in the Chilean Andes.