Claimed moons of Earth

Claimed moons of Earth are ideas or reports that there might be other natural satellites besides the Moon. Some people have wondered if Earth has more than one moon. While Earth definitely has only one large, long-term moon, the idea of extra moons has been around for hundreds of years. Over time, people have made many claims about smaller moons. Some were based on real observations, while others turned out to be mistakes or even hoaxes. Today, scientists use powerful tools like telescopes and satellites to search the skies, but no permanent second moon has ever been found. However, astronomers have discovered some strange space objects near Earth that make things more interesting. These include quasi-satellites, Earth trojans, and temporarily captured objects. While they are not true moons, they sometimes orbit near Earth or move in ways that make them seem moon-like.

The idea that Earth might have a second moon is not new. In fact, it goes back to the 1800s and even earlier. In 1846, a French astronomer named Frédéric Petit said he saw a second, smaller moon orbiting Earth very quickly. But other scientists could not see it, and later reviews showed his claim was probably a mistake. In the 1900s, this idea kept popping up, sometimes in fake stories or made-up science. Some people said they had seen or taken pictures of a second moon, but these reports were either proven false or did not have enough evidence to be trusted. A lot of the excitement came from how interested people were in space exploration.

Today, scientists do not really expect to find a second big moon orbiting Earth. Instead, they study small objects near Earth that sometimes act a bit like moons.

Quasi-satellites, which are objects that go around the Sun, not Earth, but they stay close to Earth for a long time. From Earth’s point of view, their paths look like they are looping around us. One of the best-known quasi-satellites is called 469219 Kamoʻoalewa, found in 2016. It might even be a piece of our Moon that was knocked off by an ancient impact. Another object, 3753 Cruithne, found in 1986, also behaves like a quasi-satellite. It follows a horseshoe-shaped path in space, sharing Earth’s orbit around the Sun, but it never comes close enough to be called a real moon.

Earth Trojans are a bit different. These are asteroids that stay at special places in Earth’s orbit called Lagrange points, spots where gravity is balanced. One example is 2010 TK7, which stays 60 degrees ahead of Earth in its path around the Sun. Even though these objects are not true moons, they move in step with Earth and might stay that way for a long time.

Sometimes, small space rocks like asteroids or meteoroids get caught by Earth’s gravity and start to orbit our planet for a short time. Scientists call these minimoons or temporarily captured objects (TCOs). These space visitors usually stay for only a few months or years before they either fly off into space again or burn up in Earth’s atmosphere. Only a few minimoons have ever been spotted and confirmed:

• 2006 RH₁₂₀ was captured by Earth’s gravity in 2006 and stayed for about a year before escaping back into space.
• 2020 CD₃ was caught around 2018 and orbited Earth until early 2020. It was about the size of a small car.
• 2024 PT₅ became Earth’s third confirmed minimoon in 2024.

These little moons are usually very small, only a few meters wide, about the size of a car or small house. Because they are so tiny and move in unpredictable ways, they are hard to spot with telescopes. Even though they are small, studying them is very useful. They help scientists better understand how objects move in space (called orbital mechanics) and give clues about the number and behavior of asteroids near Earth. Someday, we might even send missions to these minimoons to study them up close.

Scientists have different ways of deciding what counts as a real "moon." A traditional moon is something that orbits a planet, like Earth’s Moon, and stays in that orbit for a very long time, millions or even billions of years. But some objects, like quasi-satellites or minimoons, are a little different. Quasi-satellites orbit the Sun, not Earth, but they stay near Earth for long periods. Minimoons are only temporarily caught by Earth’s gravity and do not stick around for long. The line between what counts as a moon and what does not is still being studied. Scientists are still learning and debating how best to classify them.

Studying these unusual moons, like minimoons and quasi-satellites, is not just for fun. These small objects can actually help scientists learn a lot. Since they are close to Earth and have low gravity, they are great targets for space missions. Sending a spacecraft to one of them would be easier than going to faraway places. They also help scientists understand how Earth’s gravity affects nearby space rocks, which can tell us more about how the Earth-Moon system formed. Some of these objects might even have pieces of Earth or the Moon that were knocked off long ago. That means they could hold clues about Earth’s early history.