Is Earth's constant companion a stray asteroid or a chunk of the moon? (opens in new tab)

Earth has a group of cosmic stalkers. Known as "co-orbitals," these small bits of rock have a 1:1 mean motion resonance with Earth. Basically, they take the exact same amount of time to orbit the sun as we do. Astronomers have long believed these objects wandered in from the main asteroid belt between Mars and Jupiter, but recent spectral analysis suggests they better match the space-weathered lunar silicates that make up the moon's surface. As such, there has been an ongoing debate about whe...