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(307261) 2002 MS4 is a large classical Kuiper belt object,[2] the second-largest known object in the Solar System without a name, after (225088) 2007 OR10. It was discovered in 2002 by Chad Trujillo and Michael Brown. It is currently 47.2 AU from the Sun[7] and will come to perihelion in 2123.[4]

(307261) 2002 MS4
2002MS4 Hubble.png
2002 MS4 imaged by the Hubble Space Telescope
Discovered byChad Trujillo,
Michael E. Brown
Discovery date18 June 2002
MPC designation2002 MS4
Cubewano (MPC)[2]
ScatExt (DES)[3]
Orbital characteristics[4]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc20569 days (56.31 yr)
Earliest precovery dateApril 8, 1954
Aphelion47.740 AU (7.1418 Tm)
Perihelion35.694 AU (5.3397 Tm)
41.717 AU (6.2408 Tm)
269.45 yr (98415.8 d)
4.58 km/s
0° 0m 13.168s / day
Earth MOID34.7228 AU (5.19446 Tm)
Jupiter MOID30.7148 AU (4.59487 Tm)
Physical characteristics
Dimensions934±47 km[5]
Temperature≈ 43 K
V−R=0.38 [6]
3.5±0.4 (R-band)[5]

The Spitzer Space Telescope estimated it to have a diameter of 726±123 km.[8] The Herschel team estimates it to be 934±47 km, which would make it one of the 10 largest TNOs currently known[5] and large enough to be considered a dwarf planet under the 2006 draft proposal of the IAU.[9] Based on its size, Brown lists it as nearly certain to be a dwarf planet.[10]

Orbit of 2002 MS4 is similar but more inclined than 50000 Quaoar. Positions on 1/1/2018 are shown.

However, its low albedo suggests the opposite: dark, mid-sized bodies such as this, less than about 1000 km in diameter and with albedos less than about 0.2, have likely never been resurfaced and thus have probably not differentiated, making them highly unlikely to be dwarf planets.[11]

(307261) 2002 MS4 has been observed 55 times, with precovery images back to April 8, 1954.[4]


  1. ^ "MPEC 2002-W27 : 2002 MS4, 2002 QX47, 2002 VR128". IAU Minor Planet Center. 2002-11-21. Retrieved 2009-08-26.
  2. ^ a b "MPEC 2009-P26 :Distant Minor Planets (2009 AUG. 17.0 TT)". IAU Minor Planet Center. 2009-08-07. Retrieved 2009-08-31.
  3. ^ Marc W. Buie (2008-05-03). "Orbit Fit and Astrometric record for 02MS4". SwRI (Space Science Department). Archived from the original on 4 June 2011. Retrieved 2009-08-31.
  4. ^ a b c d "JPL Small-Body Database Browser: 307261 (2002 MS4)" (2009-09-19 last obs.). Jet Propulsion Laboratory. Retrieved 7 April 2016.
  5. ^ a b c d Vilenius, E.; Kiss, C.; Mommert, M.; et al. (2012). ""TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects". Astronomy & Astrophysics. 541: A94. arXiv:1204.0697. Bibcode:2012A&A...541A..94V. doi:10.1051/0004-6361/201118743.
  6. ^ Tegler, Stephen C. (2006-01-26). "Kuiper Belt Object Magnitudes and Surface Colors". Archived from the original on November 16, 2007. Retrieved 2006-11-05.
  7. ^ a b "AstDyS 2002MS4 Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 2009-09-04. Retrieved 2009-08-27.
  8. ^ Stansberry, Grundy, Brown, Spencer, Trilling, Cruikshank, Luc Margot Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope (2007) Preprint arXiv
  9. ^ Gingerich, Owen (2006-08-16). "The Path to Defining Planets" (PDF). Harvard-Smithsonian Center for Astrophysics and IAU EC Planet Definition Committee chair. p. 4. Retrieved 2007-03-13.
  10. ^ Michael E. Brown. "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Archived from the original on 2011-10-18. Retrieved 2011-08-25.
  11. ^ W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)', Icarus (forthcoming, available online 30 March 2019) DOI: 10.1016/j.icarus.2018.12.037,

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