Lunar Launchpads: How the Moon Might Be Creating Earth’s Orbiting Companions

In their recent study, R. Sfair and collaborators explore a fascinating possibility: that some of Earth’s strange orbital companions—called “co-orbital bodies”—might have been launched into space from the Moon itself. These bodies don’t orbit Earth like the Moon does; instead, they follow their own paths around the Sun while staying near Earth, in what scientists call “co-orbital motion.” One particularly interesting example, named Kamo’oalewa, shares a unique chemical fingerprint with lunar rocks, hinting it might be a fragment of the Moon.

Types of Co-Orbital Paths

The authors begin by explaining what co-orbital motion means. In celestial mechanics, several types of co-orbital paths exist—like horseshoe orbits, tadpole orbits, and quasi-satellite orbits. Quasi-satellites are especially intriguing because, while they loop around Earth from our perspective, they’re actually orbiting the Sun, not Earth. Until now, most researchers thought these objects came from the asteroid belt. But the Moon might be a hidden source, particularly during ancient impacts that hurled debris into space.

Simulating Lunar Ejecta

To test this idea, the team ran computer simulations of lunar debris launched into space. They modeled 54,000 tiny “test particles” ejected from all over the Moon at different speeds, ranging from just enough to escape lunar gravity to much faster. These particles then traveled through a digital Solar System that included the Sun, Earth, and Moon. The authors checked which particles ended up in co-orbital paths using a precise, automatic method that could tell the difference between various orbit types.

What the Simulations Showed

The simulations showed that about 6.7% of lunar fragments eventually moved in co-orbital paths with Earth, and nearly 2% became quasi-satellites—suggesting that this behavior isn’t just a fluke. Interestingly, the most successful particles were launched at 1.2 times the Moon’s escape velocity. These had the best chance of becoming long-lived companions, sometimes lasting thousands of years in stable orbits. Particles launched slower or much faster were less likely to stay near Earth.

Where on the Moon Do They Come From?

A major insight from the study was that where the debris comes from on the Moon matters. Particles ejected from near the equator, especially on the trailing side of the Moon (the side that faces away from its orbit), were more likely to become stable co-orbitals. This finding matches well with earlier theories and suggests that impacts near this region could explain how fragments like Kamo’oalewa got their start.

Two Pathways Into Co-Orbital Motion

The authors also noticed two kinds of behavior: “prompt” entries into co-orbital motion (soon after ejection) and “delayed” entries (hundreds of years later). This suggests that even long after an impact, lunar material can still find its way into Earth-like orbits due to the complex gravitational dance between Earth, the Moon, and the Sun. These delayed entries could keep Earth's co-orbital population replenished over time, even though major lunar impacts are rare.

Why This Study Matters

In their final remarks, the researchers point out that their findings support the lunar origin theory for objects like Kamo’oalewa and a newer discovery, 2024 PT5. While not every co-orbital object comes from the Moon, the simulations show that the Moon is a more likely source than previously thought. By identifying key factors like ejection velocity and launch location, the study adds important details to our understanding of how Earth's orbital neighborhood might be shaped by its own satellite.

Source: Sfair