Astronomers have observed a small object orbiting Earth, which they have dubbed a “mini-moon” or the planet’s “second moon”. It is actually an asteroid, about the size of a car; its diameter is about 1.9-3.5 m. And unlike our permanent Moon, the mini-moon is temporary; it will eventually break free of Earth’s orbit and go off on its own way.
Dubbed 2020 CD3, the mini-moon was discovered by Kacper Wierzchos and Teddy Pruyne of the NASA-funded Catalina Sky Survey (CSS) in Arizona on the night of February 15. The Minor Planet Center of the International Astronomical Union acknowledged the discovery: “Orbit integrations indicate that this object is temporarily bound to the Earth… Further observations and dynamical studies are strongly encouraged.”
When an asteroid’s orbit crosses Earth’s orbit, it can sometimes be captured into the latter orbit. This is what happened with 2020 CD3. It is now orbiting at a distance farther from Earth. Such an asteroid is called a Temporarily Captured Object (TCO). The orbit of such objects is unstable. They have to contend with the gravitational influence of our permanent Moon as well as that of the Sun. Once caught in Earth’s orbit, such objects usually remain for a few years before they break free and go into independent orbit around the Sun.
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According to the researchers, 2020 CD3 was captured into Earth’s orbit over three years ago. For CSS, it is only the second such discovery. It previously discovered 2006 RH120, which orbited Earth for some time that year, before it escaped in 2007.
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