What Are Quasi-Moons?

A quasi-moon, also called a quasi-satellite, is a small celestial body that appears to orbit Earth but actually circles the Sun. These fascinating objects travel around the Sun in a path nearly identical to Earth's, creating the illusion that they are secondary moons. They remain near our planet for centuries, tracing complex loops in the sky.

Unlike our true Moon, quasi-moons are not gravitationally bound to Earth. Instead, they are in a 1:1 orbital resonance — meaning they complete one orbit around the Sun in roughly the same time as Earth. This unique relationship allows them to stay close, yet never be captured.

How Quasi-Moons Orbit

From Earth’s perspective, a quasi-moon seems to loop around our planet in a slow, graceful motion. However, in reality, it’s orbiting the Sun — not Earth. Its motion results from a delicate gravitational balance between the Sun and our planet, placing it in what’s known as a co-orbital configuration.

These objects can shift between different orbital states over time, such as becoming a horseshoe orbit companion before returning to a quasi-satellite state. Gravitational influences from other planets, particularly Jupiter and Venus, constantly nudge their orbits.

Types of Co-Orbital Objects

• Trojans – Objects orbiting near a planet’s Lagrange points (L4 or L5).
• Horseshoe Orbiters – Follow a horseshoe-shaped path relative to a planet.
• Quasi-Satellites – Appear to orbit a planet while actually orbiting the Sun.

Known Quasi-Moons of Earth