(47171) 1999 TC36

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(47171) 1999 TC36
1999 TC36 seen as a binary using the Hubble in 2001
Discovered by E. P. Rubenstein,
L.-G. Strolger
Discovery date October 1, 1999
MPC designation (47171) 1999 TC36
Trans-Neptunian object
Orbital characteristics
Epoch 4 November 2013 (JD 2456600.5)
Aphelion 48.544 AU
Perihelion 30.555 AU
39.550 AU
Eccentricity 0.22742
248.73 a (90848 d)
4.67 km/s
Inclination 8.40991°
Known satellites S/2001 (47171) 1:
(0.746±0.06)×1018 kg[4]
Physical characteristics

Assuming equal albedos



[3](effective system diameter)
Mass (12.75±0.06)×1018 kg (A1+A2+B)[4]
(14.20±0.05)×1018 kg (A1+A2)[4]
Mean density
0.039–0.020 m/s2
0.117–0.096 km/s
Albedo 0.079+0.013
Temperature ≈45–44 K
Spectral type
B−V= 1.00±0.13
V−R= 0.70±0.03[3]

(47171) 1999 TC36 (also written: (47171) 1999 TC36) is a system comprising three trans-Neptunian objects (TNOs). It was discovered in 1999,[6] by Eric P. Rubenstein and Louis-Gregory Strolger during an observing run at Kitt Peak National Observatory (KPNO). Dr. Rubenstein was searching images taken by Dr. Strolger as part of the Low-Z Supernova Search program. It is classified as a plutino with a 2:3 mean-motion resonance with Neptune,[1] and, currently only being 30.5 AU from the Sun,[5] is among the brighter TNOs. It reached perihelion in July 2015.

Physical characteristics[edit]

(47171) 1999 TC36 is a triple system consisting of a central primary, which is itself a binary, and a small moon (component B).[4] The combined observations by the infrared Spitzer Space Telescope,[7] Herschel Space Telescope[3] and the Hubble Space Telescope (HST) make it possible to estimate the sizes of the components and consequently provide the range of possible values for the objects’ bulk density.[4] The single-body diameter (effective system size) of 1999 TC36 is currently estimated at 393.1+25.2

The very low estimated density of 0.3–0.8 g/cm3 obtained in 2006 (when the system was thought to be a binary) would require an unusually high porosity of 50–75%, assuming an equal mixture of rock and ice.[7] The direct measurement of visible fluxes of all three components of the system in 2009 by the HST has resulted in an improved average density of 0.532+0.317
confirming the earlier conclusion that the object is probably a rubble pile.[4] The density was revised up to 0.64+0.15
in 2012 when new information from the Herschel became available. For a bulk density in the range 1–2 g/cm3 the porosity is in the range 36–68%, again confirming that the object is a rubble pile.[3]

1999 TC36 has a very red spectral slope in visible light[8] and a flat spectrum in near infrared. There is also a weak absorption feature near the wavelength of 2 μm, probably caused by water ice. The best model reproducing the near infrared spectrum includes tholins, crystalline water ice, and serpentine as surface materials. These results are for the integrated spectrum of all three components of the system.[9]


The moon, discovered from 8 December 2001 observations by C. A. Trujillo and M. E. Brown using the Hubble Space Telescope and announced on 10 January 2002,[10] has an estimated diameter of 132+8
[3] and a semi-major axis of 7411±12 km, orbiting its primary in 50.302±0.001 d.[4] The moon is estimated to only have a mass of about 0.75×1018 kg.[4]

In 2009, analysis of Hubble images revealed that the primary is itself composed of two similar-sized components.[4] This central pair has a semi-major axis of around 867 km and a period of about 1.9 days.[4] Assuming equal albedos of about 0.079, the primary components are approximately A1=272+17
and A2=251+16
in diameter.[3] The component B orbits the barycenter of the A1+A2 system. The system mass estimated from the motion of the component B is (12.75±0.06)×1018 kg.[4] The orbital motion of the A1 and A2 components gives somewhat a higher estimated mass of (14.20±0.05)×1018 kg. The discrepancy is probably related to unaccounted gravitational interactions of the components in a complex triple system.[4]


There exist two main hypotheses on how the triple system of 1999 TC36 formed. The first one is a giant collision and subsequent reaccretion in the disc. The second one is gravitational capture of a third object by a preexisting binary. The similar sizes of A1 and A2 components favor the latter hypothesis.[4]


1999 TC36 was suggested as a target for New Horizons 2, a proposed twin of its namesake that would fly by Jupiter, Uranus, and up to four KBOs.[11]


  1. ^ a b "MPEC 2009-V05 :Distant Minor Planets (2009 NOV. 15.0 TT)". IAU Minor Planet Center. 2009-11-03. Retrieved 2009-12-10. 
  2. ^ Marc W. Buie (2005-08-31). "Orbit Fit and Astrometric record for 47171". SwRI (Space Science Department). Retrieved 2008-07-24. 
  3. ^ a b c d e f g h i j k Mommert, Michael; Harris, A. W.; Kiss, C.; Pál, A.; Santos-Sanz, P.; Stansberry, J.; Delsanti, A.; Vilenius, E.; Müller, T. G.; Peixinho, N.; Lellouch, E.; Szalai, N.; Henry, F.; Duffard, R.; Fornasier, S.; Hartogh, P.; Mueller, M.; Ortiz, J. L.; Protopapa, S.; Rengel, M.; Thirouin, A. (May 2012). "TNOs are cool: A survey of the trans-Neptunian region—V. Physical characterization of 18 Plutinos using Herschel-PACS observations". Astronomy & Astrophysics 541: A93. arXiv:1202.3657. Bibcode:2012A&A...541A..93M. doi:10.1051/0004-6361/201118562. 
  4. ^ a b c d e f g h i j k l m Benecchi, S.D; Noll, K. S.; Grundy, W. M.; Levison, H. F. (2010). "(47171) 1999 TC36, A Transneptunian Triple". Icarus 207 (2): 978–991. arXiv:0912.2074. Bibcode:2010Icar..207..978B. doi:10.1016/j.icarus.2009.12.017. 
  5. ^ a b "AstDys (47171) 1999TC36 Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-12-07. 
  6. ^ "MPEC 1999-Y19 :Distant Minor Planets (1999 DEC. 21.8 UT)". IAU Minor Planet Center. 1999-12-21. Retrieved 2015-05-08. 
  7. ^ a b J. Stansberry; W. Grundy; J-L. Margot; D. Cruikshank; J. Emery; G. Rieke; D. Trilling (2006). "The Albedo, Size, and Density of Binary Kuiper Belt Object (47171) 1999 TC36". The Astrophysical Journal 643 (1): 556–566. arXiv:astro-ph/0602316. Bibcode:2006ApJ...643..556S. doi:10.1086/502674. 
  8. ^ Doressoundiram, A.; Peixinho, N.; Moullet, A.; Fornasier, S.; Barucci, M. A.; Beuzit, J. -L.; Veillet, C. (2007). "The Meudon Multicolor Survey (2MS) of Centaurs and Trans-Neptunian Objects: From Visible to Infrared Colors". The Astronomical Journal 134 (6): 2186. Bibcode:2007AJ....134.2186D. doi:10.1086/522783. 
  9. ^ Protopapa, S.; Alvarez-Candal, A.; et al. (2009). "ESO large program about transneptunian objects: surface variations on (47171) 1999 TC36". Astronomy and Astrophysics 501 (1): 375–380. Bibcode:2009A&A...501..375P. doi:10.1051/0004-6361/200810572. 
  10. ^ "IAU Circular No. 7787". International Astronomical Union. Retrieved 2008-12-06. 
  11. ^ Stern, Alan; et al. "New Horizons 2" (pdf). NASA (Outer Planets Assessment Group). Retrieved 13 May 2012.  parent

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