Astronomy:2010 WC9

2010 WC₉

Orbit of 2010 WC9 with positions before 2018 flyby
Discovery
Discovered by	Catalina Sky Srvy.
Discovery site	Catalina Stn. (first observed only)
Discovery date	30 November 2010
Designations
MPC designation	2010 WC9
Alternative designations	ZJ99C60
Minor planet category	NEO Apollo
Orbital characteristics
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	7.45 yr (2,721 d)
|{{{apsis}}}|helion}}	1.3797 AU
|{{{apsis}}}|helion}}	0.7784 AU
Semi-major axis	1.0791 AU
Eccentricity	0.2786
Orbital period	1.12 yr (409 d)
Mean anomaly	251.06°
Mean motion	0° 52m 45.48s / day
Inclination	17.994°
Longitude of ascending node	54.655°
|{{{apsis}}}|helion}}	273.53°
Earth MOID	0.00138 AU (0.5454 LD)
Venus MOID	0.158 AU (23,600,000 km)
Physical characteristics
Mean diameter	60–130 m 60 m (est. at 0.20) 130 m (est. at 0.04)
Rotation period	8–20 minutes
Absolute magnitude (H)	23.5

2010 WC₉, unofficially designated ZJ99C60, is a sub-kilometer near-Earth asteroid of the Apollo group, approximately 100 meters (330 feet) in diameter. First observed for eleven days by the Catalina Sky Survey in 2010, the asteroid was recovered in May 2018 during its sub-lunar close encounter with Earth.

First observation and recovery

2010 WC₉ was first observed by astronomers with the Catalina Sky Survey on 30 November 2010 with a 1-day observation arc and was observed through 10 December 2010. By 10 December 2010, the asteroid was more than 24 million kilometers from Earth at apparent magnitude 21.8 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. The 10-day observation arc showed the asteroid would pass about 0.026 astronomical unit|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. It was removed from the Sentry Risk Table on 10 May 2018 and is not an impact threat for the next 100 years or more. The asteroid now has a secure 7-year observation arc.

Orbit and classification

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 0.78–1.4 AU once every 13 months (409 days; semi-major axis of 1.08 AU). Its orbit has an eccentricity of 0.28 and an inclination of 18° with respect to the ecliptic.

Using an epoch of 23 March 2018, the object had a minimum orbital intersection distance with Earth of 206,000 km (0.00138 AU), or 0.55 lunar distances (LD).

2018 approach

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. It was expected to reach apparent magnitude +11 at closest approach, 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).

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

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

Physical characteristics

Diameter

As the asteroid has not been directly resolved by telescope, its diameter can only be estimated based on the distance and brightness. Based on a generic magnitude-to-diameter conversion, it is estimated to measure between 60 and 130 meters in diameter, for an absolute magnitude of 23.5, and an assumed albedo of 0.04–0.20.

Numbering and naming

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

See also

• List of asteroid close approaches to Earth in 2018

External links

• "Lost" asteroid to pass closely May 15 Eddie Irizarry, 12 May 2018
• Asteroid 2010 WC9 to flyby Earth at 0.53 LD on 15 May
• List Of Apollo Minor Planets (by designation), Minor Planet Center
• 2010 WC9 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemeris · Obs prediction · Orbital info · MOID · Proper elements · Obs info · Close · Physical info · NEOCC
• 2010 WC9 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical Properties · Summary
• 2010 WC9 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters