What is a quasi-moon?
A quasi-moon is a space object that shares Earth’s path around the Sun but does not orbit Earth as our Moon does. Instead, it follows a similar journey to Earth, appearing to drift alongside us year after year. These companions are held mainly by the Sun’s gravity rather than Earth’s, and they are sighted only when their quiet ballet brushes the edge of our planetary neighborhood.
How quasi-moons differ from true satellites
Unlike the Moon, which is firmly bound to Earth and completes a full orbit each month, a quasi-moon is not gravitationally captured by Earth. It travels around the Sun in a way that keeps it near Earth for extended periods, but its actual orbital path is much larger and more nuanced. This distinction means quasi-moons are better thought of as travelling partners rather than conventional satellites, drifting in and out of Earth’s vicinity over long timescales.
The recent discovery: 2023 FW13
A recent find has brought attention to Earth’s silent companions: 2023 FW13, a small asteroid estimated to be between 15 and 20 metres wide. Astronomers confirmed that this object has moved in sync with Earth since at least the 1960s. By combining observations from powerful telescopes in Hawaii and Arizona, researchers traced its path back for more than six decades. 2023 FW13 is dark and faint, which is why it remained hidden from earlier sky surveys until modern instruments grew sensitive enough to detect it.
How 2023 FW13 orbits Earth
The orbit of 2023 FW13 is not a simple, circular loop around our planet. Instead, it follows a horseshoe-shaped path relative to Earth, swinging ahead of us and then trailing behind as both move around the Sun together. At times it drifts as far as about 14 million kilometres from Earth—roughly 40 times the distance to the Moon—yet it remains gravitationally linked to our planet for extended intervals. This delicate dance explains why such objects can co-exist with Earth for long periods without being captured as conventional satellites.
Why quasi-moons matter to science
Quasi-moons like 2023 FW13 offer scientists a natural laboratory to test gravitational theories. Their orbits help researchers refine models of how small bodies move under the influence of the Sun and planets, improving our understanding of solar system dynamics. They also provide clues about the origin of near-Earth asteroids and how some small bodies can enter and linger in Earth’s neighborhood for decades or even centuries. In the broader field of planetary defense, tracking such objects enhances our ability to detect potentially hazardous rocks early and predict their future trajectories with greater accuracy.
Kamoʻoalewa and the growing family of quasi-moons
Beyond 2023 FW13, a handful of quasi-moons have been identified near Earth, with Kamoʻoalewa often cited as one of the best-known examples. Each discovery reveals that Earth’s cosmic surroundings are more dynamic than once thought. Most quasi-moons remain near Earth for only limited periods before their orbits drift, but some, like 2023 FW13, appear to stay in our vicinity much longer, prompting ongoing monitoring and study.
What comes next for researchers
Astronomers plan continued tracking of 2023 FW13 and similar objects to map how their orbits evolve as time passes. By keeping close watch on these bodies, scientists hope to uncover their origins, assess how many such companions exist, and sharpen techniques for spotting faint rocks that share Earth’s path. Quasi-moons remind us that Earth’s space environment is a living, ever-changing place where even small wanderers can reveal big truths about gravity, history, and the architecture of the solar system.
These silent companions help keep the story of Earth’s cosmic encounters alive, guiding future explorations and deepening our appreciation for the intricate gravitational choreography that surrounds our planet.
