Imagine tiny bits of the Moon, blasted off its surface, not floating aimlessly but actually being captured by Earth’s gravity for a while. New research suggests this isn’t just possible, but likely happens all the time, with potentially several “lunar minimoons” circling our planet temporarily, though they are challenging to spot due to their small size and speed.
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What Exactly is a Minimoon?
A minimoon is essentially a space rock that gets caught by Earth’s gravity and orbits our planet temporarily before usually escaping back into an orbit around the sun. While there’s no official definition from groups like the International Astronomical Union, scientists often consider an object a minimoon if it’s temporarily bound to Earth, completes at least one orbit, and comes closer than about four times the Earth-moon distance during its journey.
Think of Earth and the sun in a cosmic dance. Sometimes, smaller objects join this dance, and if they get close enough to Earth, our gravity might pull them into a temporary spin around us before the sun’s pull or other forces send them on their way again. Minimoons can theoretically come from anywhere in the solar system, but a 2018 study previously suggested most might originate from the asteroid belt between Mars and Jupiter.
Closeup view of several irregularly shaped grey space rocks.
The Surprise: Minimoons from the Moon?
Recent discoveries have thrown a fascinating new possibility into the mix: what if some minimoons aren’t from far-off asteroids, but from our very own Moon? When objects collide with the Moon, they send showers of lunar material flying into space. While most falls back or is caught by the sun’s gravity, a small fraction could potentially get nudged into Earth’s orbit.
The discovery of two specific objects supports this idea. In 2016, telescopes spotted Kamo’oalewa (or 469219 Kamo’oalewa), a near-Earth object orbiting the sun in sync with Earth. Later analysis suggested Kamo’oalewa was likely a piece of the Moon ejected millions of years ago, possibly from the impact that formed the Giordano Bruno crater. More recently, in 2023, astronomers found another temporary satellite, 2024 PT5, which also appears to have a lunar origin, looking more like Moon rock than a typical asteroid.
How Many Lunar Minimoons Are Out There?
These two discoveries prompted researchers like Robert Jedicke at the University of Hawaii to simulate how lunar debris behaves after impacts. Published in the journal Icarus, their simulations suggest that a significant portion of material blasted from the Moon could be temporarily captured by Earth. About a fifth of these captured fragments might then qualify as minimoons.
Based on these simulations, the study nominally predicts that around 6.5 lunar-born satellites could be orbiting Earth at any given time. It’s “kind of like a square dance, where partners change regularly and sometimes leave the dance floor for a while,” Jedicke told Space.com, explaining the temporary nature. A typical lunar minimoon might dance around Earth for about nine months before moving on.
However, Jedicke stresses that this predicted number has “ginormous” uncertainty, meaning it could be much higher or lower. This is because scientists don’t precisely know factors like the exact size and speed distribution of material ejected during lunar impacts. If the number were truly that high, current telescopes might have spotted more by now. This uncertainty is part of the scientific process; finding more of these objects in the future will help refine the predictions and teach us more about how craters form on the Moon.
Artistic illustration showing Earth orbiting with its large Moon and a much smaller, temporary minimoon nearby.
Why Are They So Hard to Find?
Despite the predictions, spotting these temporary lunar visitors is a significant challenge. Most fragments are estimated to be quite small, only about 3 to 7 feet (1 to 2 meters) in diameter – roughly the size of a car or SUV.
Detecting such small objects in the vastness of space requires them to be relatively close to be bright enough. But when they are close, they appear to zip quickly across the sky from our perspective on Earth. Telescopes performing massive sky surveys use computers to look for moving objects, but fast-moving minimoons might appear as streaks, or “trails,” on images rather than distinct dots. These trails are much harder for computer algorithms to identify compared to slow-moving spots.
Even so, successful detections like 2020 CD3 (another temporary satellite observed briefly) show that current surveys can spot them, even if only occasionally. Once an object is identified, tracking it becomes easier as astronomers know exactly where to look.
Why These Cosmic Visitors Matter
Beyond the sheer coolness of having tiny pieces of the Moon orbiting us, studying lunar minimoons could offer valuable insights. Scientifically, understanding how debris is launched from the Moon during impacts helps us better estimate the risks and effects of asteroid impacts on Earth. It also provides clues about the history and evolution of the entire solar system.
These brief visitors also hold potential practical value. Since they are already orbiting Earth, they would require far less fuel to reach than objects in the main asteroid belt. This makes them intriguing targets for future commercial ventures interested in extracting resources like water or minerals from space rocks.
As telescopes and detection methods improve, we may find ourselves tracking more of these temporary lunar satellites, unlocking new secrets about our nearest cosmic neighbor and the space rocks that travel through our corner of the solar system.
