Every year, Earth's gravity briefly captures countless asteroids and fragments of the Moon itself in a delicate cosmic dance.
For centuries, we've known of only one natural satellite orbiting our planet—the Moon. Yet, astronomers have discovered Earth is constantly accompanied by temporary companions: minimoons and quasi-moons. These small asteroids, some as tiny as a car, become briefly entangled in Earth's gravitational field, orbiting our planet for months before sailing back into space.
The recent discovery of 2025 PN7, a quasi-moon that has traveled alongside Earth unseen for 60 years, highlights how much we still have to learn about our immediate cosmic neighborhood 1 5 . The study of these transitory companions is unlocking secrets about solar system formation and may pave the way for future asteroid mining.
Earth may host over six minimoons larger than 1 meter at any given time, constantly replenished as others depart 2 .
While often mentioned together, minimoons and quasi-moons represent different types of gravitational relationships with Earth:
These are asteroids temporarily captured by Earth's gravity, making them true temporary satellites that complete at least one full orbit around our planet. They typically remain for less than a year before escaping back into solar orbit 7 .
About 1% of minimoons eventually hit Earth, though most burn up harmlessly in the atmosphere 7 .
| Characteristic | Minimoons | Quasi-Moons |
|---|---|---|
| Orbital Relationship | Temporarily orbit Earth | Orbit the Sun while appearing to orbit Earth |
| Typical Duration | Several months to a year 5 | Decades to centuries 1 |
| Gravitational Binding | Gravitationally bound to Earth 7 | Not gravitationally bound to Earth 6 |
| Example | 2024 PT5 (orbited in 2024) 1 | 2025 PN7, Kamo'oalewa 1 |
Minimoon Orbit
Quasi-moon Apparent Orbit
A crucial 2025 study published in Icarus sought to determine whether material ejected from the Moon could explain the population of minimoons and other temporarily bound objects near Earth 2 . Researchers created sophisticated computer simulations modeling how fragments are ejected from the Moon's surface during asteroid impacts and how their orbits evolve over time.
Researchers modeled asteroid impacts on the lunar surface, calculating the size, speed, and trajectory distribution of ejected material. The simulation particularly focused on debris achieving escape velocity from the Moon .
Using gravitational physics models, the team tracked how these lunar fragments evolved over time under the gravitational influences of the Sun, Earth, and other solar system bodies .
The simulation identified which particles became temporarily bound to the Earth-Moon system, meeting the specific energy criteria for temporary capture 9 .
By scaling up these results based on known lunar impact rates, researchers estimated the steady-state population of lunar-derived minimoons .
The simulation yielded fascinating results that challenge previous assumptions:
of lunar ejecta that escapes the Moon's gravity becomes temporarily bound to the Earth-Moon system
of these bound objects meet the precise definition of minimoons
minimoons of lunar origin larger than 1 meter estimated in the Earth-Moon system at any time
| Object Type | Estimated Population | Diameter Range | Notes |
|---|---|---|---|
| All TBOs | 36 objects per year | >1 meter | Temporarily Bound Objects |
| Standard TBOs | 30 objects | 1-2 meters | Majority due to steep size distribution |
| Minimoons | 6.5 objects at any time | >1 meter | 18% of TBOs become minimoons |
These findings are scientifically important because they suggest we can study lunar geology without traveling to the Moon itself—fragments of the Moon periodically come to us 2 . Understanding this process also helps models of material exchange between planetary bodies and provides insights into impact dynamics on the Moon.
Studying these faint, fast-moving objects requires sophisticated technology and methodologies.
| Research Tool | Function | Example/Specification |
|---|---|---|
| Pan-STARRS Telescope | Discovers faint, fast-moving near-Earth objects | Located on HaleakalÄ volcano, Hawaii; discovered 2025 PN7 1 |
| Catalina Sky Survey | Detects and tracks near-Earth objects | Discovered first verified minimoon, 2006 RH120 9 |
| JPL Horizons System | Models solar system dynamics and orbits | Analyzed 2025 PN7's orbital evolution 4 |
| Spectrographs | Determines object composition by analyzing light | Suggested lunar origin of 2024 PT5 and Kamo'oalewa 2 |
| All-Sky Camera Networks | Detects fireballs from impacting minimoons | European Fireball Network 9 |
The study of minimoons and quasi-moons has evolved from theoretical speculation to an active field of research with remarkable potential. As detection technology improves, particularly with the upcoming Large Synoptic Survey Telescope, astronomers expect to discover many more of these transitory companions 9 .
What was once "well known"—that Earth has only one natural satellite—has been replaced by the understanding that our planet exists within a dynamic cloud of temporary companions, each with its own story to tell about the history and evolution of our solar system.
The next decade promises significant advances, with planned missions to quasi-moons and increasingly sophisticated tracking of these elusive objects. As Carlos de la Fuente Marcos notes, "The Solar System is full of surprises so we keep looking" 1 . In the subtle gravitational dances of minimoons and quasi-moons, we may find keys to understanding our cosmic neighborhood and advancing our capabilities as a spacefaring civilization.
This article is based on current astronomical research and may be updated as new discoveries emerge.