An Asteroid Is Swinging By Earth Today For Its Closest Visit In 400 Years

Earth is welcoming a rather hefty visitor to the neighborhood Wednesday — an asteroid that hasn't swung by these parts in roughly 400 years. About as big as the Rock of Gibraltar, asteroid 2014 JO25 is coming so close that its visit should be visible even to small telescopes.

But no need to panic, NASA says.

"Although there is absolutely no chance that the asteroid will collide with our planet, this will be a very close approach for an asteroid of this size," the space agency says in a statement.

At its closest approach, which should occur around midday ET Wednesday, the asteroid will be a little over a million miles away — or about 4.6 times the distance from Earth to the moon. Though NASA says that distance is comfortable enough to ensure there will be no collision, it is nevertheless classified as a "potentially hazardous asteroid" due to the way its orbit intersects Earth's.

First spotted in 2014 by astronomers at the Catalina Sky Survey — a collaboration between NASA's Near-Earth Objects Observation Program and the University of Arizona — JO25 looks a bit like a big barbell.

"The asteroid has a contact binary structure — two lobes connected by a neck-like region," explains Shantanu Naidu, a scientist from NASA's Jet Propulsion Laboratory. The agency says the larger of these lobes is a little more than a third of a mile wide.

But astronomers hope the visit will yield more information about its size, shape and surface features. Over the next several days, they will be probing it with deep space radar, a technique the Goldstone Solar System Radar in California's Mojave Desert has already used to cobble together 30 grainy — yet illuminating — images of the asteroid from multiple angles.

It will be another decade before an asteroid of JO25's size passes by Earth. As member station KQED notes, 1999 AN10 is expected to buzz by Earth in 2027 at a distance roughly equivalent to the space between Earth and the moon.

It'll be a much longer wait to see JO25 again, though. Astronomers say it won't return to these parts for another half a millennium.

So, amateur space-sleuths, don't miss your chance to catch it before it goes.

Either point your telescopes toward the constellation Coma Berenices, which KQED reports the asteroid will be passing through, or just let Slooh Community Observatory do it for you. The network of telescope feeds will be live-streaming the event starting at 7 p.m. ET Wednesday.

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