2017 YZ4: Newly-discovered Asteroid to Come Close to Earth Today

Katherine Hignett

Updated | On Christmas Day, astronomers at the Mount Lemmon Survey near Tucson, Arizona, discovered an asteroid fast approaching Earth. The newly-named 2017 YZ4 will skim past Earth today. 

Fast and furious

Hurtling through space at almost 21,500 miles per hour, the previously unknown rock will fly by closer than the moon. It is believed to measure between 22.6 and 49 feet in diameter according to observation news website, The Watchers.

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The asteroid's trajectory is marked in green. The orbit of the moon is drawn in grey. NASA

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Lindley Johnson, Planetary Defense Officer at NASA's Science Mission Directorate in Washington, D.C, tells Newsweek: “2017 YZ4 is the 52nd known asteroid to fly by Earth within one lunar distance this year and the first since two such asteroids flew past us on November 21. They varied from 1 to 80 meters (3 to 260 feet) in size.”

Unusually close flyby

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The asteroid will pass between the Earth and the moon Judy Schmidt/Jens Meyer/NASA/Flickr

But don’t head for your nearest underground shelter just yet. Even at its closest, the asteroid is incredibly unlikely to breach the Earth’s atmosphere. Astronomers predict its closest approach won’t get nearer than 0.00150 astronomical units—or about 139,433 miles, to the rest of us.

This is unusually close for a celestial boulder, which NASA considers a “near Earth asteroid.” This designation is reserved for any asteroid closer than six million miles to Earth.

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Johnson tells Newsweek, “As of December 25, there are 17,506 known Near-Earth Objects (NEOs), in orbits around the Sun that could come close to our planet; 17,400 are asteroids and 106 are comets.

“This year, we’ve discovered 1,996 Near Earth Asteroids so far. There were 1887 such objects discovered in 2016 and 1,566 in 2015."

Celestial objects pass by the Earth regularly. Few, however, strike orbit so close to home. NASA’s Jet Propulsion Laboratory compiles a list of upcoming near-Earth flybys which can help you make sure you build your underground fallout shelter on time. Or, of course, just get out your telescope.

There are many more asteroids like this waiting to be discovered, Johnson explains."Near Earth Asteroids are never 'new,'" he says. "They’ve been there for many millennia. We just haven’t discovered them all yet."

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Busy winter skies

This has been a big month for stargazers, with 2017’s only supermoon and the Geminid meteor shower. The Geminids brought us a “potentially hazardous” 3200 Phaethon asteroid, imaged in new detail by the newly-restored Arecibo Observatory Planetary Radar in Puerto Rico. The second-largest single-dish radio telescope in the world was damaged by Hurricane Maria earlier this year.


If astronomers are wrong about 2017 YZ4, and the asteroid is about it hit Earth, we only have a few hours to tunnel underground. The boulder will reach its closest approach at 10:56 ET (7:56 PCT)—give or take six minutes.

This article has been updated to include quotes from NASA's Lindley Johnson.

This article was first written by Newsweek

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