This Asteroid Discovered A Year Ago Turns Out To Be 2 In Orbit With Each Other

It's only been months since the near-Earth asteroid 2017 YE5 was discovered, but now it appears that it's not one, but two rocks.

The binary system consists of a pair of asteroids of nearly identical mass at around 3,000 feet in size. This is quite rare and only the fourth "equal mass" binary system that's ever been recorded. Most of the binary systems that have been witnessed consist of two objects of wildly different sizes.

A Unique Discovery

The near-Earth object was first spotted by the Morocco Oukaimeden Sky Survey on Dec. 21, 2017, according to release from NASA. Back then, very little observations have been made of what's believed to be a regular asteroid.

Several months later, 2017 YE5 brushed close to Earth, making its closest approach in the next 170 years. The relatively close proximity of the asteroid to within 3.7 million miles of Earth allowed scientists to observe it more closely.

Three of the Earth's largest radio telescopes independently confirm the 2017 YE5 as a binary system.

First to suggest the prospect is NASA's Goldstone Solar System Radar, which observed two distinct lobes. However, the angle of the rotating system made it difficult for scientists to see if the two objects were actually separated. Eventually, the rotation of the binary system exposed a gap between the duo, confirming that they are indeed two separate asteroids.

A few days after the Goldstone's initial observations, the Arecibo Observatory in Puerto Rico and the Green Bank Observatory in West Virginia, United States both independently confirmed it: 2017 YE5 is a binary system of two equally sized asteroids.

About 2017 YE5

Aside from its nature as a binary system, other new details about this near-Earth object has also been revealed from its close fly-by past Earth. Brian Warner, who's from the Center for Solar System Studies in Rancho Cucamonga, California, analyzed visible-light data from the system, determining that the two rocks orbit each other once every 20 to 24 hours.

Further observations reveal that the objects are bigger than what their optical brightness indicate, which makes it likely very dark-colored.

Surprisingly, even if this is one of the few equal mass binary systems ever seen by humans, the Goldstone images show that there's a stark difference between the two objects' radar reflectivity, which is not the case in other binary systems on record. These differences suggest that there are also differences in densities, compositions near the surface of the rocks, or surface roughness.

Binary systems are actually quite common in the solar system with 15 percent of all asteroids travel with a partner. In fact, it's so common that scientists have wondered why there are so few impact craters on Earth that are identified as a doublet. Gizmodo reveals that roughly 3 percent of all impact craters are actually binary systems.