2010 WC9

2010 WC₉ was first observed by astronomers with the Catalina Sky Survey on 30 November 2010 with a 1-day observation arc^[6] and was observed through 10 December 2010.^[7] By 10 December 2010, the asteroid was more than 24 million kilometers from Earth^[6] at apparent magnitude 21.8^[1] and was becoming too faint to be practical to track.

The preliminary 10-day observation arc generated a line of variation roughly 15 million km long for May 2018 that did not intersect Earth's orbit and thus was not a 2018 impact threat.^[8] The 10-day observation arc showed the asteroid would pass about 0.026 AU (3,900,000 km; 2,400,000 mi) from Earth around late 14 May 2018. The asteroid was recovered on 8 May 2018 when it was 8 million kilometers from Earth and given the temporary NEOCP designation ZJ99C60.^[2] It was removed from the Sentry Risk Table on 10 May 2018^[9] and is not an impact threat for the next 100 years or more. The asteroid now has a secure 7-year observation arc.^[4]

2010 WC₉ is an Apollo asteroid, the largest dynamical group of near-Earth objects with nearly 10,000 known members. It orbits the Sun at a distance of 0.77–1.37 AU once every 13 months (404 days; semi-major axis of 1.07 AU). Its orbit has an eccentricity of 0.28 and an inclination of 18° with respect to the ecliptic.^[4]

Using an epoch of 21 November 2025, the object had a minimum orbital intersection distance with Earth of 1,300 km (0.00000867 AU), or 0.00338 lunar distances (LD).^[4]

On 15 May 2018, 22:05 UT, the asteroid approached Earth at just over 0.5 LD, the closest approach of this asteroid in nearly 300 years.^[3] It was expected to reach apparent magnitude +11 at closest approach,^[10] bright enough to be seen in a small telescope if you have a custom ephemeris for your location. At closest approach, it was best seen from the Southern hemisphere such as South Africa and southern South America. The asteroid passed Earth going 12.81 km/s (28,700 mph).^[4]

This was the third closest approach ever observed by an asteroid with absolute magnitude (H) brighter than 24.^[11]

Flyby in 2018: geocentric trajectory in the sky (top) and flyby from north to south, shown with hourly motion (bottom)

Animation of 2010 WC9's orbit

Around the Sun

Around the Earth

  2010 WC9 ·   Sun ·   Earth ·   Moon

As of 2018, this minor planet has neither been numbered nor named by the Minor Planet Center.^[1]

• List of asteroid close approaches to Earth in 2018