Newly discovered asteroid is much more freak than expected astronomers

When is an asteroid not an asteroid? When it's a binary pair. It turns out that an asteroid discovered at the end of last year is actually two objects related to gravitation orbiting one of the other. But this particular duo, christened 2017 YE5, belongs to an exceptionally rare class of objects close to Earth

The YE5 2017 object was spotted for the first time by astronomers at the Observatory Oukaïmeden in Morocco last December, but virtually nothing about it, beyond his presence, was known. In June, the object made the closest approach to Earth for the next 170 years, allowing scientists to take a closer look. What was initially evaluated as a single asteroid turned out to be two objects orbiting one another: a double asteroid.

Normally it looks like it's not a big problem; about 15 percent of all known asteroids larger than 200 meters in diameter are binaries. But 2017 YE5 is special because it is a binary "equal mass", in which the two objects are about the same mass. The vast majority of binaries involve an uneven pair, in which one asteroid is significantly larger than the other. Astronomers have documented tens of thousands of asteroids in the solar system, but this is only the fourth known binary of equal mass. The latest observations now offer the most detailed images ever taken of this exceptionally rare phenomenon.

The YE5 2017 arrived at less than 6 million kilometers of land on June 21, about 16 times the distance from Earth to the Moon. Using bistatic radar – a technique in which the transmitter and receiver are placed in separate locations – astronomers from NASA's California Solar System Goldstone Radar (GSSR) in California scanned the object, discovering that They had a pair of asteroids on their hands. These observations were later confirmed by astronomers from the Green Bank Observatory (GBO) in West Virginia.

Observations have shown that both asteroids are in orbit every 20 to 24 hours approximately. In addition, the asteroids were larger than expected; these rocks are very dark, about as dark as coal, making visual observations difficult. The radar scans revealed their true greatness; each asteroid is about 3,000 feet (900 meters) long. That said, their radar reflectivity patterns were extremely different, suggesting that these objects, although similar in size and mass, have different densities and / or compositions near the surface. A duo, yes, but identical twins, not so much.

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As noted, binary asteroids are a relatively common feature of the solar system. Interestingly, we sometimes see their signature on Earth in the form of "doublet" impact craters, in which the binary pair managed to stay together by entering the atmosphere of our planet and striking the surface . It is estimated that about 3% of all impact craters on Earth are these doublets. Unfortunately, this also means that if we detect an asteroid on an incoming trajectory, there is a 15% chance that it will have a partner.

[NASA]