You’ve looked up at the night sky a thousand times and seen that big, glowing rock we call the Moon. It’s consistent. It’s reliable. But lately, you might have seen headlines claiming Earth has a second moon, or a "mini-moon," or even a "quasi-moon." It sounds like science fiction, or maybe just a clickbait scheme.
So, does Earth have two moons?
The short answer is: sort of, sometimes, but not really in the way you’re thinking. We don't have a permanent, massive companion like Luna. However, our planet is surprisingly good at "kidnapping" passing asteroids and forcing them into a temporary dance around us. These are the mini-moons, and they’re way more common than most people realize.
The Case of the Temporary Mini-Moons
Most of the time, it's just us and the big guy. But every few years, a small asteroid wandering through the solar system gets a little too close. Earth’s gravity snags it. These objects are usually tiny—maybe the size of a car or a small house—and they don’t stay for long.
Take 2020 CD3, for example. Astronomers at the Catalina Sky Survey spotted this little rock in early 2020. After crunching the numbers, they realized it hadn't just arrived; it had actually been orbiting Earth for about three years already. It was a silent, invisible second moon that nobody noticed until it was almost ready to leave.
These aren't stable orbits. The tug-of-war between the Sun, the Earth, and our actual Moon eventually flings these visitors back out into deep space. They’re like cosmic houseguests who crash on your couch for a weekend and then vanish. They are technically moons while they are bound to us, but they lack the staying power to make it into the textbooks as a permanent fixture.
What About the "Ancient" Second Moon?
There is a fascinating theory in planetary science called the Big Splash or the Giant Impact Hypothesis. It suggests that billions of years ago, Earth really did have two moons—and they were both huge.
Dr. Erik Asphaug and other researchers have modeled a scenario where a smaller "companion moon" once orbited alongside the Moon we see today. Eventually, they collided. But it wasn't a fast, explosive crash. It was a "slow-motion" splat. This theory explains why the far side of the Moon is so much thicker and more mountainous than the side facing us. The second moon basically pancaked itself onto the surface of the first one.
So, if you’re asking if we ever had two moons, the answer might be a definitive yes. We just ended up with one giant one because they couldn't stay out of each other's way.
Meet 469219 Kamoʻoalewa: The Quasi-Moon
Then there’s the weird stuff. Specifically, the "quasi-moons."
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Kamoʻoalewa is a fascinating chunk of rock. It doesn't technically orbit the Earth in a traditional circle. Instead, it orbits the Sun, but it does so in a way that keeps it constantly dancing around our planet. From our perspective, it looks like it’s following us.
What makes Kamoʻoalewa special is its composition. In 2021, a study led by Ben Sharkey at the University of Arizona found that this rock looks exactly like... the Moon. Not like a typical asteroid, but like the actual lunar surface. This has led to the wild, yet scientifically grounded, theory that Kamoʻoalewa is actually a fragment of our Moon that was blasted off by an ancient impact. It’s a literal piece of "Moon Jr." following its parent around the Sun.
Why We Don't See Them
If you're wondering why you can't just walk outside with a pair of binoculars and see these other moons, it's a matter of scale.
- Size: Most mini-moons are between 1 and 10 meters wide.
- Distance: They are often much further away than the main Moon.
- Albedo: They are dark rocks that don't reflect much sunlight.
Searching for a mini-moon is like trying to find a specific grain of dark sand in a giant, pitch-black ballroom using only a dim flashlight. We only find them because of high-powered surveys like the Pan-STARRS or the upcoming Vera C. Rubin Observatory, which will likely find dozens of these things every year once it’s fully operational.
The Trojan Asteroids
Earth also has "Trojans." These are asteroids that hang out in stable gravitational pockets called Lagrange points (specifically L4 and L5). They lead or follow Earth in its orbit around the Sun.
For a long time, we only knew of one: 2010 TK7. Then, in 2022, a second one called 2020 XL5 was confirmed. These aren't moons because they don't orbit the Earth itself; they orbit the Sun with us. But they are part of our immediate cosmic neighborhood, trapped in a permanent gravitational embrace with our planet.
Why This Matters for the Future
This isn't just a fun fact for trivia night. These temporary moons are actually high-value targets for space agency missions.
Think about the logistics. If we want to mine an asteroid or learn how to deflect a "planet-killer," we usually have to travel months or years into deep space. But a mini-moon? It brings the asteroid to us. It’s essentially a free sample delivered to our doorstep. NASA and private companies like AstroForge are intensely interested in these objects because they represent the easiest possible targets for resource extraction and scientific study.
Testing hardware on a mini-moon is a lot cheaper than sending a probe to the asteroid belt. It’s the ultimate training ground for deep-space exploration.
The Verdict
So, does Earth have two moons?
If you mean "Does Earth have two permanent, large, natural satellites?" then no. The Moon is a lonely king.
But if you mean "Is Earth currently accompanied by other natural objects in its orbit?" the answer is almost always yes. We are constantly capturing and releasing tiny rocks. We have quasi-satellites that follow us like shadows. We have Trojans that share our path.
Space is crowded. We just happen to have one companion that’s loud enough to get all the attention.
How to Track Earth's "Other" Moons
If you want to keep up with the latest discoveries of mini-moons and quasi-satellites, you don't need a PhD, but you do need to know where to look.
- Follow the Minor Planet Center (MPC): This is the official clearinghouse for all small body discoveries in the solar system. When a new potential mini-moon is found, it’s listed here first.
- Check the Catalina Sky Survey: Based in Arizona, this team is responsible for finding a huge chunk of the near-Earth objects we know about. Their "Recent Discoveries" page is a goldmine for space nerds.
- Watch for the Vera C. Rubin Observatory updates: Once this telescope in Chile goes live (targeted for mid-2025/2026), our catalog of mini-moons is expected to explode. It will be performing a 10-year survey of the sky that will catch objects we never even dreamed were there.
- Use Orbit Visualizers: Websites like Project Pluto or various NASA JPL tools allow you to plug in the designation of an object (like 2020 CD3) and see exactly how it's moving relative to Earth.
Stop thinking of Earth as a solitary traveler. We’re more like a magnet, constantly picking up and dropping off little bits of solar system debris as we hurtle through the void.