From 3753 Cruithne to 2024 Discoveries: a History of Earth's Temporary Moons

Breaking down the facts behind From 3753 Cruithne to 2024 Discoveries: a History of Earth's Temporary Moons—uncover what experts are saying.

Beyond horseshoe orbits and chaotic temporary captures, the Earth-Sun system features five gravitational balance zones known as Lagrange points. In these locations, the gravitational pull of two large bodies matches the centrifugal force needed for an object to move alongside them.

Points L1, L2, and L3 sit along the line connecting Earth and the Sun, requiring active station-keeping for artificial satellites like the James Webb Space Telescope. Points L4 and L5 form equilateral triangles with Earth and the Sun, positioned 60 degrees ahead and 60 degrees behind our planet along its orbital plane. These regions function as cosmic gravity pockets capable of trapping celestial bodies indefinitely.

Astronomers call asteroids residing in these equilibrium points Trojans. While Jupiter hosts thousands of Trojan asteroids, Earth holds far fewer. Hunting for Earth Trojans requires pointing optical instruments toward the twilight sky near the Sun, a geometry fraught with glare.

Despite those observation hurdles, astronomers using the Wide-field Infrared Survey Explorer (WISE) telescope discovered Earth's first confirmed Trojan, 2010 TK7, measuring roughly 300 meters across. In December 2020, observers found a second, significantly larger companion: 2020 XL5, a kilometer-wide carbonaceous asteroid. Calculations indicate 2020 XL5 will remain stable at the L4 point for at least four thousand years before gravitational perturbations nudge it away.