Matthew Holman, a senior astrophysicist at the Smithsonian Astrophysical Observatory, was sifting through data from the Vera C. Rubin Observatory in Chile when something odd caught his eye. Running a custom-made computer program, he and his colleague Kevin Napier had already spotted more than 2,000 little bright dots in the telescope data, corresponding to newly discovered small objects in the distant solar system. But this one was different: It seemed to be big.

Holman managed his expectations. After all, astronomers in the business of finding distant objects are used to disappointment. “We all have ‘found Mars’ … in terms of a false positive,” Holman tells Smithsonian magazine. They find a bright object that seems really big, then, with a closer look, learn that it’s nothing very remarkable after all. “We’re all really cautious when you see something that looks like it’s large.”