The Earth Has a Second Moon — for Now
Earth’s gravity has pulled an asteroid off course and into orbit around the planet, turning 2020 CD3 — the space rock’s official name — into a second moon. About the size of a small car, the asteroid completes a circuit around Earth every 47 days, an orbit quite a bit longer than the 27-day pass of our OG moon.
2020 CD3’s orbit, in fact, is erratic — resembling more a knotted rope than the smooth elliptical path of our steadier moon.
“This isn’t an object that is stably orbiting the Earth like the moon is,” Eric Christensen, an astronomer with the Catalina Sky Survey, the NASA-funded, University of Arizona program that discovered the object, told The Atlantic. “This is a fairly tenuous connection to the Earth. It’s getting tugged on by the moon and tugged on by the Earth.”
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The new, mini-moon was discovered on Feb. 15, by Kacper Wierzchos and Theodore Pruyne, researchers at the Sky Survey, which is run by the University’s Lunar and Planetary Laboratory in Tuscon, Arizona. But experts believe it may have been orbiting the Earth for the past three years undetected.
Unfortunately, it may already be time to say good-bye — this new, mini-moon isn’t here to stay. Experts say it’s a temporary acquisition and the most recent observations suggest the mini-moon will escape Earth’s gravity within a few weeks. Still, “it’s a big deal as out of ~ 1 million known asteroids, this is just the second asteroid known to orbit Earth,” tweeted Wierzchos, one of the discoverers. A similarly temporary object was tugged into the orbit of Earth in 2006, and discovered by Christensen, but continued on its space journey after less than a year.
But more mini-moons are likely in Earth’s future — they may in fact already be there, just undetected. As our powers of space observation improve, it’s likely these temporary moons “will be discovered in the coming years, allowing for improved definition and characterization of this strange class of near-Earth objects,” according to a statement on the Sky Survey’s website.
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