3200 Phaethon

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3200 Phaethon
Radar image of 3200 Phaethon taken by Arecibo, December 17, 2017
Discovered by Simon Green and
John K. Davies / IRAS
Discovery date October 11, 1983
MPC designation (3200) Phaethon
Named after
1983 TB
Orbital characteristics[1]
Epoch 2017-Sep-04 (JD 2458000.5)
Uncertainty parameter 0
Observation arc 12,464 days (34.12 yr)
Aphelion 2.4025 AU (359 million km)
Perihelion 0.13991 AU (20.9 million km)
1.2712 AU (190 million km)
Eccentricity 0.88994
523.5 days (1.433 yr)
19.9 km/s (45,000 mph)
0° 41m 15.646s / day
Inclination 22.253°
Earth MOID 0.01945 AU (2.91 million km)
Venus MOID 0.0425 AU (6.36 million km)[2]
Jupiter MOID 2.7361 AU (409 million km)
TJupiter 4.511
Physical characteristics
Dimensions 5.8 km (3.6 mi)[3]
3.604 hours (0.1502 d)[1]
B-type asteroid
10.7 (2017-Dec-14)

3200 Phaethon (/ˈf.əθɒn/ FAY-ə-thon, sometimes incorrectly spelled Phaeton), provisional designation 1983 TB, is an Apollo asteroid with an orbit that brings it closer to the Sun than any other named asteroid (though there are numerous unnamed asteroids with smaller perihelia, such as (137924) 2000 BD19).[4] For this reason, it was named after the Greek myth of Phaëthon, son of the sun god Helios. It is 5.8 km (3.6 mi) in diameter[3] and is the parent body of the Geminids meteor shower of mid-December. With an observation arc of 30+ years, it has a very well determined orbit.[1] The 2017 Earth approach distance was known with an accuracy of ±40 km.[1]


Phaethon was the first asteroid to be discovered using images from a spacecraft. Simon F. Green and John K. Davies discovered it in images from October 11, 1983, while searching Infrared Astronomical Satellite (IRAS) data for moving objects. It was formally announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal, who reported it to be asteroidal in appearance. Its provisional designation was 1983 TB, and it later received the numerical designation and name 3200 Phaethon in 1985.

Orbital characteristics[edit]

The elliptical orbit of 3200 Phaethon crosses the orbits of Mars, Earth, Venus and Mercury

Phaethon is categorized as an Apollo asteroid, as its orbital semi-major axis is greater than that of the Earth's at 1.27 AU (190 million km; 118 million mi). It is also suspected to be a member of the Pallas family of asteroids.[5]

Its most remarkable distinction is that it approaches the Sun closer than any other named asteroid: its perihelion is only 0.14 AU (20.9 million km; 13.0 million mi) — less than half of Mercury's perihelial distance. It is a Mercury-, Venus-, Earth-, and Mars-crosser as a result of its high orbital eccentricity. The surface temperature at perihelion could reach around 1,025 K (750 °C; 1,390 °F).

Phaethon is a possible candidate for detecting general relativistic and/or solar oblateness effects in its orbital motion due to the frequent close approaches to the Sun.[6]

Potentially hazardous asteroid[edit]

Phaethon is categorized as a potentially hazardous asteroid (PHA),[1][7] but that does not mean there is a near-term threat of an impact. It is a potentially hazardous asteroid merely as a result of its size (absolute magnitude H ≤ 22) and Earth minimum orbit intersection distance (Earth MOID ≤ 0.05 AU).[8] The Earth minimum orbit intersection distance (E-MOID) is 0.01945 AU (2,910,000 km; 1,808,000 mi), which is defined by the shortest distance between the orbit of Phaethon and the orbit of Earth.[1] With a 30+ year observation arc, the orbit of Phaethon is very well understood with very small uncertainties.[1] Close approaches of Phaethon are well constrained for the next 400 years.[6]

Physical characteristics[edit]

Phaethon is an asteroid with fairly unusual characteristics in that its orbit more closely resembles that of a comet than an asteroid; it has been referred to as a "rock comet".[9] In recent studies performed by NASA's STEREO spacecraft, dust tails have been observed,[10] and in 2010, Phaethon was detected ejecting dust.[11] It is possible that the Sun's heat is causing fractures similar to mudcracks in a dry lake bed.[11]

Phaethon's composition fits the notion of its cometary origin; it is classified as a B-type asteroid because it is composed of dark material. Since its discovery, several other objects were found exhibiting mixed cometary and asteroidal features, such as 133P/Elst–Pizarro.

Meteor shower[edit]

Shortly after its discovery, Fred Whipple observed that the "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras".[12] In other words, Phaethon is the long-sought parent body of the Geminids meteor shower of mid-December.

Close approaches[edit]

Phaethon approached to 0.120895 AU (18,085,600 km; 11,237,900 mi) of Earth on December 10, 2007,[1] and was detected by radar at Arecibo.[6] When Phaethon came to perihelion in July 2009, it was found to be brighter than expected.[13][14] During its approach, the STEREO-A spacecraft detected an unexpected brightening, roughly by a factor of two.[9]

2010 approach[edit]

Phaethon imaged on December 25, 2010, with the 37-cm f/14 Rigel telescope at Winer Observatory by Marco Langbroek

2017 approach[edit]

On December 16, 2017, at 23:00 UT, Phaethon passed 0.06893173 AU (10,312,040 km; 6,407,605 mi) from Earth (27 lunar distances).[1] The Earth approach distance was known with a 3-sigma accuracy of ±40 km.[1][a] This was the best opportunity to date for radar observations by Goldstone and Arecibo, with a resolution of 75 meters/pixel (246 feet/pixel).[6]

The asteroid was bright enough to see in small telescopes, peaking at magnitude 10.8 between December 13–15 while dimming slightly to magnitude 11 on December 16 at closest approach.[15] Arecibo made observations of Phaethon from December 15-19.[3] It will not make an Earth approach closer than the 2017 passage until December 14, 2093, when it will pass 0.01981 AU (2,964,000 km; 1,841,000 mi) from Earth.[1][16]

Path of 3200 Phaethon in the sky during December 2017
Time lapse taken through a telescope in Riga, Latvia (December 10, 2017)
Phaethon at maximum angular velocity, December 15, 2017, 18:47:13–19:24:50 UTC


  1. ^ In 2014, JPL 374 (solution date 2014-Sep-12) showed a 2017 Earth approach distance with an accuracy of ±80 km. Math: (MAX−MIN) * AU / 2


  1. ^ a b c d e f g h i j k l m n "3200 Phaethon (1983 TB)". JPL Small-Body Database. Jet Propulsion Laboratory. Archived from the original on December 13, 2017. Retrieved December 13, 2017. 
  2. ^ "(3200) Phaethon Orbit". Minor Planet Center. Retrieved November 28, 2017. 
  3. ^ a b c Agle, D. C.; Brown, Dwayne; Farukhi, Suraiya (December 22, 2017). "Arecibo Radar Returns with Asteroid Phaethon Images". NASA. Retrieved January 8, 2018. 
  4. ^ "JPL Small-Body Database Search Engine — Constraints: asteroids and q < 0.141 (au)". JPL Small-Body Database. Jet Propulsion Laboratory. Retrieved September 5, 2011.  Take notice of the orbit condition number (the lower the number, the lower the orbit's uncertainty).
  5. ^ Jaggard, Victoria (October 12, 2010). "Exploding Clays Drive Geminids Sky Show?". National Geographic. Retrieved August 10, 2017. 
  6. ^ a b c d Benner, Lance A. M. (2017). "Goldstone Radar Observations Planning: Asteroid 3200 Phaethon". NASA/JPL Asteroid Radar Research. Retrieved November 26, 2017. 
  7. ^ Phillips, Tony (December 3, 2007). "Asteroid Shower". Science@NASA. NASA. Retrieved April 4, 2017. 
  8. ^ "NEO Groups". Near Earth Object Program. NASA. Archived from the original on November 2, 2016. 
  9. ^ a b Jewitt, David; Li, Jing (2010). "Activity in Geminid Parent (3200) Phaethon". The Astronomical Journal. 140 (5): 1519. arXiv:1009.2710Freely accessible. Bibcode:2010AJ....140.1519J. doi:10.1088/0004-6256/140/5/1519. 
  10. ^ Jewitt, David; Li, Jing; Agarwal, Jessica (2013). "The Dust Tail of Asteroid (3200) Phaethon". The Astrophysical Journal Letters. 771 (2). L36. arXiv:1306.3741Freely accessible. Bibcode:2013ApJ...771L..36J. doi:10.1088/2041-8205/771/2/L36. 
  11. ^ a b Sutherland, Paul (September 10, 2013). "Why an asteroid is crumbling into meteor dust". Skymania.com. Retrieved September 10, 2013. 
  12. ^ Whipple, F. L. (October 25, 1983). Marsden, B. G., ed. "1983 TB and the Geminid Meteors". IAU Circular. 3881. 1. Bibcode:1983IAUC.3881....1W. 
  13. ^ Shanklin, Jonathan (2009). "Comet Section: 2009 News". British Astronomical Association. Retrieved September 20, 2009. 
  14. ^ Battams, K.; Watson, A. (June 2009). "(3200) Phaethon". IAU Circular. 9054. 3. Bibcode:2009IAUC.9054....3B. 
  15. ^ "(3200) Phaethon: Ephemerides for December 2017". NEODyS-2. University of Pisa Department of Mathematics. Retrieved November 26, 2017. 
  16. ^ "(3200) Phaethon: Close Approaches". NEODyS-2. University of Pisa Department of Mathematics. Retrieved May 18, 2009. 

External links[edit]