Saturday, May 25, 2019

Huge Asteroid Passes By Earth

Radar images of 1999 KW4 taken at Goldstone. Credit: NASA

An asteroid, estimated to be over one kilometer wide, missed our planet on Saturday, May 25 at around 23:05 UTC. The space rock, designated 1999 KW4 (or 66391) passed the Earth at a safe distance of around 13.5 lunar distances (LD), what corresponds to 5.18 million kilometers.

1999 KW4 is a binary Aten-type potentially hazardous asteroid (PHA) discovered May 20, 1999 by the Lincoln Near Earth Asteroid Research (LINEAR) project. LINEAR is an MIT Lincoln Laboratory program funded by the United States Air Force and NASA, dedicated for the systematic detection and tracking of near-Earth objects (NEOs).

According to observations, 1999 KW4 has an estimated diameter of approximately 1.32 kilometers. It orbits the sun at a mean distance of about 0.64 AU, every 188 days. The object rotates around its own axis every 2.76 hours.

Arecibo radar observations have revealed that 1999 KW4 has a minor-planet moon orbiting it. The object, which received designation S/2001 (66391) 1, has a diameter of about 360 meters, and orbits the asteroid every 16 hours at a mean-distance of approximately 2.6 kilometers.

On Saturday, 1999 KW4 flew by Earth with a relative velocity of 21.5 km/s. Next close approach of this asteroid to our planet is expected next year, on May 26, when it will pass at a distance of around 63 LD (24.2 million kilometers).

On May 26, there were about 1,983 PHAs detected and none of them is on a collision course with our planet. PHAs are asteroids larger than 100 meters that can come closer to Earth than 19.5 LD (7.5 million kilometers).

To date, astronomers have discovered more than 20,200 NEOs. Only this month 117 such objects were detected.

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