"Using visible wavelengths of light, it is difficult to tell if an asteroid is big and dark, or bright and small, because both combinations reflect the same amount of light," said Carrie Nugent, a NEOWISE scientist at the Infrared Processing and Analysis Center at California Institute of Technology, in Pasadena. "But when you look at an asteroid in the infrared with NEOWISE, the amount of infrared light corresponds with how big the asteroid is, and with some thermal models on a computer, you can figure out how big the asteroids are."