Outer space is often described as vast emptiness stretching into infinity, but that’s not a definition that speaks to the lived experience of most planetary defense experts. As of September 2024, NASA estimates that there are 35,453 near-Earth asteroids, almost 25,000 of which are larger than 140 meters.
According to the space agency’s Asteroid Terrestrial-impact Last Alert System (ATLAS), a network of four 0.5-meter telescopes in Hawaii, Chile, and South Africa, the Earth will have a close run-in with one of these near-Earth chunks of rock. Due to its horseshoe-like trajectory, which will semi-orbit the planet from September 29 to November 5, the Earth will play host to a brand new mini-moon for those two months. The details of this cosmic rendezvous were published earlier this month in the journal Research Notes of the American Astronomical Society.
This new mini-moon, honored with a name only an astrophysicist could love—2024 PT5—is truly a pipsqueak. Measuring just 33 meters long, the moon isn’t even as long as a typical airliner. In fact, these moons can be so small that previous detections of potential mini-moons in the past have turned out to just be returning space debris. In 2015, for example, a ground-based observatory identified a new natural satellite orbiting Earth, only to discover 13 hours later that it was actually the ESA space observatory Gaia.