"This time it's not coming close enough (to Earth) to be any larger than a dot of light," said Paul Chodas, manager of NASA's Jet Propulsion Laboratory Center for Near Earth Object Studies.
The asteroid was previously estimated to be 2,000 feet in diameter. However, asteroids change shape over time, as they smash into other celestial objects and break apart.
What's more, the giant rock won't be at its closest until November 11, well after Halloween.
NASA says the asteroid is most likely a "dead" comet that once spewed debris across the solar system. In space talk, that means it has "shed its volatiles" that would produce the visible tail seen on some comets.
The asteroid was discovered October 10, 2015, by the University of Hawaii's Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) telescope in Haleakala, on the island of Maui.