A “potentially hazardous” asteroid has been identified using a new algorithm, which was designed to uncover near-Earth asteroids for the Vera C. Rubin Observatory’s upcoming 10-year survey of the night sky. The roughly 600-foot-long asteroid, designated 2022 SF289, was discovered during a test drive of the algorithm, using the ATLAS survey in Hawaiʻi.

Finding 2022 SF289, which poses no risk to Earth for the foreseeable future, confirms that the next-generation algorithm, known as HelioLinc3D, can identify near-Earth asteroids with fewer and more dispersed observations than today’s methods.

“By demonstrating the real-world effectiveness of the software that Rubin will use to look for thousands of yet-unknown potentially hazardous asteroids, the discovery of 2022 SF289 makes us all safer,” said Ari Heinze, the principal developer of HelioLinc3D. The former postdoctoral researcher at the University of Hawaiʻi Insтιтute for Astronomy (IfA) is now a researcher at the University of Washington.

Potentially hazardous asteroids

The solar system is home to tens of millions of rocky bodies ranging from small asteroids not larger than a few feet, to dwarf planets the size of our moon. Most of these bodies are distant, but a number orbit close to the Earth, and are known as near-Earth objects. The closest of these—those with a trajectory that takes them within about 5 million miles of Earth’s orbit, or about 20 times the distance from Earth to the moon—warrant special attention. Such “potentially hazardous asteroids,” or PHAs, are systematically searched for and monitored to ensure they won’t collide with Earth, a potentially devastating event.

Scientists search for PHAs using specialized telescope systems such as the NASA-funded ATLAS survey, run by a team at IfA. They do so by taking images of parts of the sky at least four times every night. A discovery is made when they notice a point of light moving unambiguously in a straight line over the image series. Scientists have discovered about 2,350 PHAs using this method, but estimate that at least as many more await discovery.

Joining the hunt

From its peak in the Chilean Andes, the Vera C. Rubin Observatory is set to join the hunt for these objects in early 2025. Funded primarily by the U.S. National Science Foundation and the U.S. Department of Energy, Rubin’s observations will dramatically increase the discovery rate of PHAs. Rubin will scan the sky with unprecedented speed using its 8.4-meter mirror and mᴀssive 3,200-megapixel camera, visiting spots on the sky twice per night rather than the four times needed by present telescopes. This novel observing “cadence,” required a new type of discovery algorithm to reliably spot space rocks.

Rubin’s solar system software team at the University of Washington’s Insтιтute for Data-intensive Research in Astrophysics and Cosmology has been working to develop such codes. Along with Smithsonian senior astrophysicist and Harvard University lecturer Matthew Holman, who in 2018 pioneered a new class of heliocentric asteroid search algorithms, Heinze and Siegfried Eggl, an ᴀssistant professor at the University of Illinois at Urbana-Champaign, developed HelioLinc3D: a code that could find asteroids in Rubin’s dataset. With Rubin still under construction, Heinze and Eggl wanted to test HelioLinc3D to see if it could discover a new asteroid in existing data, one with too few observations to be discovered by today’s conventional algorithms.

John Tonry and Larry Denneau, lead ATLAS astronomers, offered their data for a test. The Rubin team set HelioLinc3D to search through this data, and, on July 18, 2023, it spotted its first PHA: 2022 SF289, initially imaged by ATLAS on September 19, 2022, when it was 13 million miles from Earth.

Other surveys had also missed 2022 SF289, because it was pᴀssing in front of the rich starfields of the Milky Way. However, additional observations from Pan-STARRS and Catalina Sky Survey quickly confirmed the discovery.

For more information, see the University of Washington press release.