2020 CD3: Earth’s Latest Mini-Moon

Some planets have dozens of moons. Jupiter, for example, has 79 moons. Others have no moons, like Mercury and Venus. Most people believe Earth has only one moon: the one on which Neil Armstrong took one small step for man, but one giant leap for mankind. For a year, however, they have been mistaken. Kacper Wierzchos and Teddy Pruyne, astronomers at the Mount Lemmon Observatory in Tucson, Arizona, discovered on February 15, 2020 a tiny asteroid captured by Earth’s gravity: a mini-moon. Its name is 2020 CD3. Estimated to be only six to 12 feet in diameter (the size of a car), scientists believe the mini-moon entered Earth’s orbit sometime between 2016 and 2018. It orbited Earth until March 2020. and it began traveling to the Sun.

2020 CD3 has a relatively low speed, which is likely why Earth’s gravity was able to capture it. Unlike the Moon’s orbit, which is elliptical, 2020 CD3’s orbit around Earth was a long, twisted path, with several loops and turns, like a knot that’s impossible to untie. It adopted this chaotic orbit under the influence of not only by Earth’s gravity but also that of the Moon and Sun. These multiple gravitational forces are also what caused 2020 CD3’s escape from Earth’s orbit and into the Sun’s. Though it’s unclear when this officially occurred, scientists estimate that it was around March 7, 2020. This constant dance between the gravitational forces of Earth, the Sun, and the Moon will continue, however, and 2020 CD3 will not be gone from Earth forever. It is expected to pass again in August 2038, or in another 25 to 50 years, according to Eric Christensen, the director of the Catalina Sky Survey. The Catalina Sky Survey is the NASA-funded project through which 2020 CD3 was discovered.

The future of 2020 CD3 once it returns near Earth is unclear. It’s possible that 2020 CD3 will not be pulled into Earth’s orbit again. But if it does orbit again, scientists do not know when it would leave. Scientists also acknowledge the possibility of its collision with Earth if it enters another geocentric orbit. Its recent orbit was so chaotic that it neared Earth several times, so a collision would not be impossible. Unfortunately, there is virtually no straightforward way to precisely predict 2020 CD3’s future path due to the combination of the gravitational forces of Earth, the Moon, and the Sun.

Some scientists even predict that the Earth constantly has mini-moons, but they are too small to detect—even smaller than 2020 CD3. Grigori Fedorets, an astronomer at Queen’s University Belfast, predicts that with more advanced technology, astronomers could discover a new mini-moon every few months. Whether or not Earth has more mini-moons, the discovery of 2020 CB3 proved that though the Moon may be Earth’s only natural satellite, it is certainly not its only satellite.

Minimoons might also be useful for space exploration: they could be destinations for human exploration as a way to visit an asteroid without needing to travel farther than the Moon. They could also be used for low-budget robotic space probes. Lastly, they can also be used as logical places to run early experiments—it would be faster than a mission into the asteroid belt. As Dr. Robert Jedicke, who is based at the University of Hawaii, said, “I hope that humans will someday venture in the solar system to explore the planets, asteroids, and comet—and I see mini-moons as the first stepping stones on that voyage.”

2020 CD3 is not the first of Earth’s mini-moon to be discovered. French astronomer Frederic Petit noticed a second moon circling 11 kilometers above the Earth’s surface in 1846. This discovery seemed implausible: the boundary between Earth and space is set at 80 kilometers by the Karman line, and such an orbit would decay almost immediately due to atmospheric drag. Nevertheless, it got media attention. Jules Verne incorporated the idea of mini-moons into his novel “From the Earth to the Moon.” The concept has been continuously discovered and focused on; the German astronomer Georg Waltemath noticed a mini-moon in 1898. Clyde Tombaugh, who discovered Pluto, spent four years in the 1950s looking for mini-moons.

Since then, there have been reports of debris patches with the same orbit as the Moon—but either 60 degrees ahead or behind it; these zones are called Lagrange Points. A Hungarian research team believes these dust clouds exist but don’t qualify as moons. Then, in 2006, Eric Christensen discovered a 2006 RH120 in orbit around the Earth. Though it was small and seemed like it might be an old piece of NASA’s Apollo hardware, it officially became the earth’s second moon.

If scientists can spot more mini-moons, they will be able to study space rocks much more efficiently. Mini-moons can provide insights on space rocks without having to research the asteroid belt hundreds of millions of kilometers away from Earth. If scientists can predict a mini-moon’s orbit despite its chaotic nature and locate it to collect samples, the wonders of outer space could be discovered closer to home.