Earth is about to briefly capture a bus-sized asteroid.buradaki/Getty ImagesEarth is getting a second moon, a mini-moon asteroid called 2024 PT5, on September 29.This asteroid from the Arjuna asteroid belt will follow a horseshoe path around Earth for 57 days.Astrophotographers may capture images, but it's too faint for most amateur telescopes to see.Earth is about to pluck a second moon from an asteroid belt — but we only get this mini-moon for 57 days.It's an asteroid about the size of a school bus, at 35 feet long, and it has a typical, un-snazzy asteroid name: 2024 PT5.Earth is poised to pick up this hitchhiker from the nearby Arjuna asteroid belt on September 29.According to a paper published in the Research Notes of the American Astronomical Society this month, the 2024 PT5 asteroid will then be in the grasp of Earth's gravity, following a horseshoe-like path around our planet until November 25, when it will return to an orbit around the sun.NASA's profile of 2024 PT5.NASA Eyes on Asteroids"You may say that if a true satellite is like a customer buying goods inside a store, objects like 2024 PT5 are window shoppers," Carlos de la Fuente Marcos, the paper's lead author, told Space.com.The asteroid poses no threat to Earth.You'll probably only see the mini-moon in photosThis mini-moon is nothing like our real moon.