Trio of observatories reveal rare double asteroid
Observations by three of the world’s largest radio telescopes have revealed that a near-Earth asteroid discovered in 2017 is actually two objects, each about 3,000 feet (900 meters) in size, orbiting each other. The two bodies are nearly equal in mass and not touching each other.
Near-Earth asteroid 2017 YE5 was discovered on Dec. 21, 2017 by the Morocco Oukaimeden Sky Survey (MOSS), but no details were known about the asteroid’s physical characteristics until last month. 2017 YE5 is only the fourth “equal mass” binary near-Earth asteroid ever discovered. The most recent observations provide the most detailed images of this type of binary asteroid ever obtained.
On June 21, the asteroid made its closest approach to Earth for at least the next 170 years, coming to within 3.7 million miles (6 million kilometers) of Earth, or approximately 16 times the distance between the Earth and the Moon. NASA’s Goldstone Solar System Radar (GSSR) in California made observations on June 21 and 22 that provided the fist indications that asteroid 2017 YE5 could be a binary system. The observations showed two distinct lobes, but astronomers could not determine if the two bodies were connected or separated.
On June 24, astronomers at the Arecibo Observatory in Puerto Rico collaborated with their colleagues at the Green Bank Observatory (GBO) in West Virgina to use their observatories in a bi-static radar configuration (Arecibo transmitted the radar signal and Green Bank received the return signal). Working together, they were able to confirm that 2017 YE5 consists of two separate bodies. Both Goldstone and Arecibo had independently confirmed the asteroid’s binary nature by June 26.
The new observations show that the two bodies revolve around each other once every 20 to 24 hours. Radar images show that the two objects are larger than suggested by their optical brightness, indicating that they do not reflect as much sunlight as a typical rocky asteroid. Images taken by Goldstone on June 21 show a striking difference in radar reflectivity between the two objects, suggesting that they may have different densities, near-surface compositions, or different surface roughnesses.
The discovery of YE5’s binary nature provides researchers with an important opportunity to increase understanding of different types of binary asteroids and to study the formation mechanisms of binaries and contact binaries. The combined radar and optical observations of YE5 may allow researchers to estimate the densities of the two objects, giving researchers a better understanding of their composition, internal structure and how they formed.
Video courtesy of NASA/JPL-Caltech
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.