Earth's new space neighbour is a temporary mini-moon

The Washington Post

The object is about the size of a car and was spotted by the NASA-funded Catalina Sky Survey

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Earth has acquired a second “mini-moon” about the size of a car, according to astronomers who spotted the object circling our planet.

The mass – roughly 1.9 to 3.5 metres in diameter – was observed by researchers Kacper Wierzchos and Teddy Pruyne at the NASA-funded Catalina Sky Survey that focuses on the search for near-Earth objects, in particular on any potentially hazardous asteroid that may pose a threat of impact, in Arizona on the night of February 15.
“BIG NEWS. Earth has a new temporarily captured object/Possible mini-moon called 2020 CD3, likely to be a C-type asteroid,” Wierzchos tweeted.

The astronomer said it was a “big deal” as “this is just the second asteroid known to orbit Earth (after 2006 RH120, which was also discovered by the Catalina Sky Survey).” Its route suggests it entered Earth’s orbit three years ago, he said.

The only other asteroid known to orbit Earth, 2006 RH120, rotated the planet from September 2006 to June 2007.

Lesson plan: Incoming asteroids! 

The Smithsonian Astrophysical Observatory’s Minor Planet Centre, which collects data on minor planets and asteroids, in an announcement said “no link to a known artificial object has been found,” implying it was likely an asteroid captured by Earth’s gravity. “Orbit integrations indicate that this object is temporarily bound to the Earth.”

Earth’s new neighbour is not in a stable orbit around the planet and is unlikely to be around for very long. “It is heading away from the Earth-moon system as we speak,” Grigori Fedorets, research fellow at Queen’s University Belfast in Northern Ireland, told New Scientist magazine, and escaped last month.

Asteroid? Meteor? Comet? Here's how to tell the difference

A meteor is what happens when a meteoroid – a small piece of an asteroid – burns up upon entering Earth’s atmosphere, creating a streak of light in the sky.

Sometimes one asteroid can smash into another. This can cause small pieces of the asteroid to break off. Those pieces are called meteoroids. Meteoroids can also come from comets.

Graphic: Doris Wai/SCMP

If a meteoroid comes close enough to Earth and enters Earth’s atmosphere, it vaporises and turns into a meteor: a streak of light in the sky. Because of their appearance, these streaks of light are sometimes called "shooting stars." But meteors are not actually stars.

Comets orbit the Sun, like asteroids. But they are made of ice and dust not rock. As a comet’s orbit takes it toward the Sun, the ice and dust begin to vaporise. That vaporised ice and dust become the comet’s tail. You can see a comet even when it is very far from Earth. However, when you see a meteor, it’s in our atmosphere.