At a Glance

When astronomers discovered object 2017 YE5 in December 217, they believed it was a simple NEO, or near-Earth object. Using three of the world's largest telescopes, astronomers soonrealized the "asteroid" was a binary system made of up two 3,000-foot bodies.

An asteroid discovered orbiting the sun last year had a surprise waiting for scientists to uncover: It'sactually two asteroids lockedin a binary orbit.

Aoccurs when two astronomical objects are close enough that their gravitational attraction causes them to orbit each other. Earth and its moon are an example of this.

When astronomers discovered object 2017 YE5 in December, they believed it was a simple NEO, or near-Earth object.

When it made its closest flyby, passing just 3.7 million milesfrom Earth on June 21, scientists at the Arecibo Observatory in Puerto Rico and the Green Bank Observatory in West Virginia teamed up to get a betterlook at the object and , according to a NASA press release.

Using three of the world's largest telescopes, the team soonrealized the "asteroid" was a binary system made of up two bodies that are roughly 3,000 feet wide eachthat revolvearound each other once every 20 to 24 hours.

Roughly 15 percent of asteroids larger than 650 feet are binary systems, so they are not uncommon. Typically, they are comprised of a large body revolving around a much smaller satellite.

Binaries of equal mass like 2017 YE5 are much rarer, NASA notes.

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The scientists also discovered the bodies were larger than previously thought becausethey are not very reflective, suggesting they are charcoal in color.

A final curious feature was also noted. The two bodies reflect radar signals differently, suggesting differences in their densities,surface composition, surface roughnessor a combination of these characteristics.

One theory is that they were two separate bodies that got pulled into orbit at some point when they neared each other in space.

The binary asteroid and its uniquefeatures havepiqued the curiosity of the astronomers, who say the discovery "provides scientists with an important opportunity to improve understanding of different types of binaries and to study the formation mechanisms between binaries and contact binaries, which may be related."