The first known interstellar object to visit our solar system — named ‘Oumuamua — was detected in October 2017 by Hawaii’s Pan-STARRS 1 telescope. But it was too faint for NASA’s Spitzer Space Telescope to detect when it looked more than two months after the object’s closest approach to Earth in early September. That ‘non-detection’ puts a new limit on how large the strange object can be, astronomers now report.