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2016 WF9 is an asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group.[3][4] The asteroid is somewhat dark, and possibly an extinct comet, but without the comet-like dust and gas cloud.[2] It was detected on 27 November 2016 by NEOWISE, the asteroid-and-comet-hunting portion of the Wide-Field Infrared Survey Explorer (WISE) mission.[2] According to NEOWISE, “2016 WF9 could have cometary origins. This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface.”[5] 2016 WF9 is about 0.5–1.0 km (0.3–0.6 mi) across so is "relatively large" for a near-Earth object.[2]

2016 WF9
PIA21259 - Celestial Object 2016 WF9, a NEOWISE Discovery (Artist Concept).jpg
2016 WF9 (artist rendition)
Discovery [1][2]
Discovered by NEOWISE project
Discovery site NEOWISE
Discovery date 27 November 2016
Apollo · NEO · PHA[3]
Orbital characteristics[3]

Epoch 2457800.5 (2017-Feb-16.0) TDB[3]

Reference: JPL 11 (heliocentric ecliptic J2000)[3]
Uncertainty parameter 5
Observation arc 111 days
Aphelion 4.759 AU[3]
Perihelion 0.9817 AU[3]
2.870 AU[3]
Eccentricity 0.6580[3]
4.86 yr (1776 days)[3]
3.004 deg[3]
Inclination 14.99 deg[3]
125.4 deg[3]
342.4 deg[3]
Earth MOID 0.014 AU
Jupiter MOID 0.52 AU[3]
Jupiter Tisserand parameter 2.893 (comet-like)
Physical characteristics
Dimensions 0.5–1.0 km (0.3–0.6 mi)[2]
<0.05 (dark)


2017 approachEdit

2016 WF9 passed Earth on 25 February 2017 at a distance of 0.3407 AU (50,970,000 km; 31,670,000 mi) and is not considered a threat for the foreseeable future.[2][3] The 2017 approach did not bring it particularly close to Earth.[2] In December 1944 it passed about 0.19 AU (28,000,000 km; 18,000,000 mi) from Earth and in February 2149 it will pass about 0.06 AU (9,000,000 km; 5,600,000 mi) from Earth.[3]


When 2016 WF9 was first announced and had a short insignificant 3 day observation arc, it was estimated to have a 7.6 year orbital period.[1] The preliminary orbit was also listed on the JPL Sentry Risk Table, but none of the virtual impact dates were before 2029.[6] As the observation arc became longer and the orbital parameters better constrained, it was removed from the Sentry Risk Table on 20 December 2016.[7] With a 111-day observation arc, it is now known that it has a 4.86 year orbital period and currently stays inside the orbit of Jupiter.[3]

A simulation of 2016 WF9's dynamics over a period of 100 million days (~274,000 years) found that it had roughly a 60% chance of originating from the outer solar system as a long-period comet.[8]

Orbit of 2016 WF9 on 25 February 2017, closest approach to Earth.[3]

See alsoEdit


  1. ^ a b "MPEC 2016-W125: 2016 WF9". IAU Minor Planet Center. 2016-11-30. Retrieved 2017-02-02.  (K16W09F)
  2. ^ a b c d e f g Agle, DC; Cantillo, Laurie; Brown, Dwayne (29 December 2016). "NASA's NEOWISE Mission Spies One Comet, Maybe Two". NASA. Retrieved 29 December 2016. 
  3. ^ a b c d e f g h i j k l m n o p q r s t Park, Ryan S.; Chamberlin, Alan B. (30 December 2016). "JPL Small-Body Database Browser (2016 WF9)". JPL. Retrieved 30 December 2016. 
  4. ^ a b MPC
  5. ^ Williams, Matt (30 December 2016). "NASA’S NEOWISE Missions Spots New Comets". Universe Today. Retrieved 31 December 2016. 
  6. ^ "Tracking News". hohmanntransfer. 2016-12-01. Retrieved 2017-02-02. 
  7. ^ "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Retrieved 2017-02-02. 
  8. ^ Odasso, Alessandro (9 January 2017). "2016 WF9 - a simulation based on Jan 5th orbital params". Retrieved 9 January 2017. 

External linksEdit