Rare Double Asteroid Detected Near Earth In June

An exotic asteroid that swung by us last month reveals it has a twin of identical size.

Artist's concept of binary asteroid 2017 YE5.
NASA/JPL-Caltech

An exotic asteroid that swung by us last month reveals it has a twin of identical size.

First discovered last December, near-Earth asteroid 2017 YE5 was initially believed to have a binary structure, composed of two lobes joint by a narrowing middle — much like the famous comet C7P, which took Twitter by storm in April, the Inquisitr reported at the time.

But it seems the curious asteroid was actually hiding a twin, and that the two lobes were, in fact, two separate space rocks circling each other in a tight orbit.

The announcement came yesterday from NASA, which observed this exotic pair with its Goldstone Solar System Radar (GSSR) in California and uncovered that asteroid 2017 YE5 is even more special than we imagined.

One of the surprising things about 2017 YE5 is that the two space rocks that make up this binary asteroid (as it’s called) are the same size, each measuring about 3,000 feet (900 meters) across.

This is extremely rare in binary asteroids, as most pairs usually have one larger asteroid and a satellite that orbits it. Only three other similar cases have been discovered so far, which classifies 2017 YE5 as a veritable curio.

But even more fascinating is that the twin asteroids known as 2017 YE5 may not even be related. It’s entirely possible that these equal-mass asteroids were originally two separate objects that got sucked into a common orbit when they came across each other while traveling through the solar system.

How do we know all this? Well, when 2017 YE5 was first spotted, we had no clue about its physical properties. But the chance to study the asteroid in more detail arose in late June when the space rock popped by for a close visit.

On June 21, 2017, YE5 made its closest approach to Earth, coming within 3.7 million miles (6 million kilometers) of our planet. That’s roughly 16 times the distance from here to the moon, NASA points out.

While the asteroid goes around the sun on an elliptical path every 4.74 years — it takes it 1,730 days to complete a full orbit, notes Science Alert — and is bound to swing back really soon, it will be another 170 years before it comes as close to Earth as it did last month.

This June visit afforded astronomers an unexpected opportunity to take a better look at 2017 YE5. The first to confirm its true identity was the GSSR, which scrutinized the asteroid on June 21 and 22.

Two days later, the Arecibo Observatory in Puerto Rico and the Green Bank Observatory (GBO) in West Virginia teamed up to examine 2017 YE5 through a technique called bistatic radar, in which Arecibo beamed a radar signal to the asteroid and the GBO picked up the return signal.

Observations from the three giant radio telescopes revealed that the twin asteroids orbit one another every 20 to 24 hours and that they’re actually bigger than the initial brightness observations suggested. This means that 2017 YE5 reflects less light than your typical rocky asteroid and “is likely as dark as charcoal,” states NASA.

Another peculiar thing about the twin asteroids is that they reflect the radar signal from the telescope in different ways. This indicates that the space rocks are not identical twins, as Space.com puts it, and probably have different densities, surface textures, or even compositions.

If this is true, then the space rocks may have originated from different places and were brought together to form a binary asteroid.