A discovery by the astronomers at the Pan-STARRS observatory in Maui, Hawaii, shows that the Earth has a “second moon,” or a quasi-moon. A quasi-moon isn’t really a moon at all however, it’s just a small asteroid that has decided to tag along with Earth for a while.

The Pan-STARRS observatory is a facility located on the summit of Haleakalā, it is a 1.8-meter telescope that operates as part of the Haleakalā High Altitude Observatories site. The astronomers at Pan-STARRS announced the discovery of the asteroid – named 2025 PN7 – in August of this year, but when looking back at old images they can see that 2025 PN7 has been around since 1957, almost 70 years.

The reason scientists and astronomers alike haven’t found the quasi-moon 2025 PN7 until now is because it is very small and is difficult to spot with older telescopes. It can only be detected when it passes relatively close to Earth, and these visibility windows are rare. 

It has an estimated diameter of only 62 to 98 feet (19 to 30 meters), roughly the size of a city bus, which in space, doesn’t reflect a whole lot of light, which adds to the complications of spotting it.

A fun fact about quasi-moons is that they actually orbit the sun, not the Earth but the orbital path it has closely resembles the one that Earth follows, however it is not gravitationally bound to our planet like a true moon. 

This explains why 2025 PN7 is a quasi-moon and not a mini-moon that orbits Earth – like 2024 PT5. Quasi-moons also tend to stick around a little longer than mini-moons, and 2025 PN7 is on track to stay with us until 2083.

From our perspective, 2025 PN7 actually appears to move in a looping, or figure-eight path, which made it challenging to track and identify as a stable, more long-term companion in space until a few months ago.

To quiet some concerns, asteroid 2025 PN7 is not dangerous at all, and there is no scientific evidence it will threaten the Earth in any way. It’s actually a good thing – it allows scientists to observe and test asteroid samples without having to travel to the asteroid belt.

Scientists estimate that there are at least six other quasi moons currently sharing Earth’s orbital zone. These objects are temporary by nature: over decades or centuries their orbits evolve, and they may transition out of quasi satellite motion into other arrangements (such as “horseshoe” or “trojan” orbits).

Most excitingly, quasi moons are relatively accessible targets for scientific exploration, and because they originate from the broader asteroid population, they can give us insight into solar system formation, the near Earth object environment, and potential future mission planning!