Times Earth Actually Had A Second Moon

Unlike many of the other planets in our solar system, Earth only has one moon. Or, at least, that's true most of the time. Sometimes, our planet attracts another satellite or mini-moon but usually just for a short period of time. And, as far as researchers have confirmed, it has happened multiple times with at least four asteroids.

The first mini-moon attracted by Earth was Asteroid 2022 NX1, which is 5 to 15 meters in size. Researchers have determined that it orbited our planet for 98 days from October 1980 to January 1981, but just 19 days after leaving, it returned and stayed for 29 days. At the time, it was the first near-Earth object to experience multiple captures in a single close-encounter event. In 2022, the asteroid made another return to Earth's gravitational pull, this time only for a single capture of 21 days. In between 2022 NX1's visits, researchers discovered 1991 VG was briefly captured by Earth's gravity during a fly-by that spanned from November 1991 to April 1992. The asteroid came into telescope view again in May 2017, and observations revealed that, this time around, the 10-meter object wasn't considered a mini-moon because it followed a very similar orbit as Earth around the Sun.

However, Asteroid 2006 RH120 was a mini-moon of Earth for much longer — more than a year. From late May 2006 to late July 2007, the 5-meter asteroid orbited our planet three times. Asteroid 2020 CD3 was also captured by Earth's gravity for an extended period. When researchers identified the 1-meter object in February 2020, they estimated that it had been orbiting the planet for about a year before it was flung back into space in early March 2020.

Unfortunately, scientists are still trying to understand fully the variations at play regarding the temporary capture of asteroids by Earth's gravity. They do know, though, that the orbits of space objects change over time, mainly because of gravitational perturbations, which are disturbances in the motion of objects because of other objects' gravitational forces.

One example of this is how comets orbit the Sun. Another is Asteroid 2024 PT5, which some researchers initially predicted would be captured by Earth's gravitational pull in September 2024. However, NASA's observation of the object found that its orbital trajectory around the Sun is too far away from our planet for that to happen. If it ever gets closer to Earth because of gravitational perturbations, there's a possibility that the planet's gravity will draw it in.

Similarly, the Moon affects Earth's seasons because its own gravitational force counteracts the planet's wobble on its axis, creating a relatively stable climate. However, the secondary satellites that temporarily orbit our planet don't have any considerable effect because their small size means that they have weak gravitational pull and because they're still too far away for that pull to have any noticeable effect.