The first trans-Neptunian object (TNO) was discovered in 1992. Given the small size of TNOs and their considerable distance from the Sun, it was years before sizes were first measured for a few TNOs. For a variety of reasons (direct and indirect), TNOs are believed related to comets which are generally quite dark. The conventional wisdom has been a best estimate of 0.04 for the albedo of TNOs.
Accumulated measurements of size and albedo now suggest that, while some TNOs are indeed this dark, some are significantly brighter. Reported measurements are summarized below.
The above graph shows albedo vs. diameter for trans-Neptunian objects and centaurs for which diameters have been measured. Pluto and Charon are also included. Red points indicate TNOs, blue points indicate centaurs, and black points Pluto and Charon.
Most size determinations have been made by comparing thermal and visual observations. Some have been derived for binary TNOs by combining observed brightness, orbital dynamics, and reasonable assumed values of density. A few diameter measurements come from direct imaging or stellar occultations.
Approximate average albedos are as follows (with number of objects in parentheses):
The relevant diameter measurements are listed below. This includes 20 TNOs (of which 6 are binary), 5 centaurs, and Pluto and Charon (for these two, representative measurements are given). All other diameter estimates on the pages Trans-Neptunian objects and List of known trans-Neptunian objects assume an albedo of 0.09. This is a revision in 2005 from a previous model (the old model assumed albedos of 0.09 for Centaurs, 0.04 for TNOs less than 660 km in diameter, and an increasing albedo for larger TNOs based on a best fit to observations through early 2004).
Measured diameters:
| designation | #/name | type | H mag. | diameter (km) | albedo | method | source |
|---|---|---|---|---|---|---|---|
| Pluto | planet | [-1.0] | 2302±12 2320±23 2328±46 <2408 | 0.44-0.61 (B) 0.6 (V) -- -- | eclipses imaging eclipses occultation |
Tholen, Buie (1990) Albrecht et ali (1994) Young, Binzel (1994) Agner, Elliot (1996) | |
| Charon | satellite | [0.9] | 1186±26 >1203 1285±26 1242±41 1212±3 | 0.378±0.015 (B) -- 0.285±0.015 (V) -- -- | eclipses occultation imaging eclipses occultation |
Tholen, Buie (1990) Elliot, Young (1991) Albrecht et ali (1994) Young, Binzel (1994) Person et ali (2006 link) | |
| 1977 HZ | (2060) Chiron | centaur | 6.5 | 182±8 168±20 180±13 160±20 148±8 142±10 | 0.14±0.06/0.03 0.13±0.04/0.03 0.148±0.022 0.14±0.02 0.17±0.02 0.11±0.02 | thermal thermal occultation thermal thermal thermal |
Campins et ali (1994) Altenhoff, Stumpff (1995) Bus et ali (1996) Groussin, Peschke, Lamy (2000) Fernandez, Jewitt, Sheppard (2002) Groussin, Lamy, Jorda (2004) |
| 1992 AD | (5145) Pholus | centaur | 7.0 | 189±26 185±16 | 0.044±0.013 0.043±0.020 | thermal thermal |
Davies et ali (1993) Davies, Tholen, Ballantyne (1996) |
| 1995 GO | (8405) Asbolus | centaur | 9.0 | 66±4 78±8 | 0.12±0.03 0.095±0.015 | thermal thermal |
Fernandez, Jewitt, Sheppard (2002) Stansberry et ali (2005) |
| 1997 CU26 | (10199) Chariklo | centaur | 6.4 | 302±30 273±19 236±12 225±25 | 0.045±0.010 0.055±0.008 0.07±0.01 0.10±0.02 | thermal thermal thermal thermal |
Jewitt, Kalas (1998) Altenhoff, Menten, Bertoldi (2001) Groussin, Lamy, Jorda (2004) Stansberry et ali (2005) |
| 1993 SC | (15789) | plutino | 6.9 | 328±58/66 398±108/171 | 0.022±0.013/0.006 0.035±0.016/0.013 (R) | thermal thermal |
Thomas et ali (2000) Grundy, Noll, Stephens (2005) |
| 1996 TL66 | (15874) | SDO | 5.4 | 632±84/98 <958 | 0.030±0.012/0.007 >0.018 (R) | thermal thermal |
Thomas et ali (2000) Grundy, Noll, Stephens (2005) |
| 1996 TP66 | (15875) | plutino | 6.8 | 350±50 | 0.03±0.01 | thermal | Stansberry et ali (2005) |
| 1996 TO66 | (19308) | cubewano | 4.5 | <897 <902 | >0.04 >0.033 (R) | thermal thermal |
Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) |
| 1998 WH24 | (19521) Chaos | cubewano | 4.9 | <742 <747 | >0.04 >0.058 (R) | thermal thermal |
Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) |
| 2000 WR106 | (20000) Varuna | cubewano | 3.7 | 900±129/145 1060±180/220 936±238/324 600±150 | 0.07±0.03/0.02 (R) 0.038±0.022/0.010 0.049±0.011/0.014 (R) 0.21±0.09 | thermal thermal thermal thermal |
Jewitt, Aussel, Evans (2001) Lellouch et ali (2002) Grundy, Noll, Stephens (2005) Stansberry et ali (2005) |
| 1995 SM55 | (24835) | cubewano | 4.8 | <701 <704 | >0.04 >0.067 (R) | thermal thermal |
Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) |
| 1998 SM165 | (26308) | cubewano, 1:2 res. (binary) | 5.8 | 238±54* | 0.14±0.06 (R) | dynamical | Grundy, Noll, Stephens (2005) |
| 2001 KX76 | (28978) Ixion | plutino | 3.2 | 1055±165 <804 <822 475±75 | 0.09 >0.15 >0.148 (R) 0.375±0.125 | thermal thermal thermal thermal |
Bertoldi et ali (2002 link)* Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) Stansberry et ali (2005) |
| 1999 TD10 | (29981) | SDO | 8.8 | 90±15 | 0.075±0.025 | thermal | Stansberry et ali (2005) |
| 1999 UG5 | (31824) Elatus | centaur | 10.1 | 47±2 | [0.07] | photometric | Peixinho et ali (2001) |
| 2001 PT13 | (32532) Thereus | centaur | 9.0 | 80±5 | 0.098±0.012 | thermal | Stansberry et ali (2005) |
| 2000 EB173 | (38628) Huya | plutino | 4.7 | <540 <548 480±50 | >0.08 >0.084 (R) 0.11±0.02 | thermal thermal thermal |
Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) Stansberry et ali (2005) |
| 2002 CR46 | (42355) | SDO | 7.2 | 155±15 | 0.10±0.02 | thermal | Stansberry et ali (2005) |
| 1999 TC36 | (47171) | plutino (binary) | 4.9 | 675±100# 609±93/47# 301±68* 375±50# 405±65/55# | 0.035 0.05±0.01 0.22±0.01 (R) 0.15±0.04 0.079±0.031/0.024 | thermal thermal dynamical thermal thermal |
Bertoldi et ali (2002 link)* Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) Stansberry et ali (2005) Stansberry et ali (2006) |
| 2002 LM60 | (50000) Quaoar | cubewano | 2.6 | 1200±200 1260±190 1260±190 | 0.12 0.092±0.036/0.023 (R) 0.10±0.03 (R) | thermal imaging imaging |
Bertoldi et ali (2002 link)* Brown, Trujillo (2004) Grundy, Noll, Stephens (2005) |
| 1998 SG35 | (52872) Okyrhoe | centaur | 11.3 | 45±5 | 0.030±0.005 | thermal | Stansberry et ali (2005) |
| 2000 QC243 | (54598) Bienor | centaur | 7.6 | 175±25 | 0.055±0.015 | thermal | Stansberry et ali (2005) |
| 2002 AW197 | (55565) | cubewano | 3.3 | 886±115/131 700±50 | 0.101±0.038/0.022 0.17±0.03 | thermal thermal |
Margot et ali (2002) Cruikshank et ali (2005) |
| 2002 TX300 | (55636) | cubewano | 3.3 | <906 <709 | >0.085 >0.19 (R) | thermal thermal |
Ortiz et ali (2004) Grundy, Noll, Stephens (2005) |
| 1997 CQ29 | (58534) | cubewano (binary) | 6.6 | 80* 77±18* | 0.37 (R) 0.39±0.17 (R) | dynamical dynamical |
Noll et ali (2004) Grundy, Noll, Stephens (2005) |
| 2000 EC98 | (60558) Echeclus | centaur | 9.5 | 70±15 | 0.125±0.045 | thermal | Stansberry et ali (2005) |
| 1999 RZ253 | (66652) | cubewano (binary) | 5.9 | 166* 170±39* | 0.12±0.01 (B) 0.29±0.12 (R) | dynamical dynamical |
Noll et ali (2004) Grundy, Noll, Stephens (2005) |
| 2002 TC302 | (84522) | SDO, 2:5 resonance | 3.9 | <1195 <1211 | >0.04 >0.051 (R) | thermal thermal |
Altenhoff, Bertoldi, Menten (2004) Grundy, Noll, Stephens (2005) |
| 2001 QT297 | (88611) | cubewano (binary) | 5.5 | 88±10* 168±38* [290#] | 0.115±0.025 0.10±0.04 0.13 | dynamical dynamical dynamical |
Osip, Kern, Elliot (2003) Grundy, Noll, Stephens (2005) Kern, Elliot (2006) |
| 2003 VB12 | (90377) Sedna | Oort cloud object | 1.6 | 1700 <1800 | >0.20 0.046 (R) | thermal/ imaging |
Brown, Trujillo, Rabinowitz (2004) Grundy, Noll, Stephens (2005) |
| 1998 WW31 and S/2000 (1998 WW31) 1 | cubewano (binary) | 6.1 | 129±19/9* 152±35* | 0.071±0.015/0.017 0.060±0.026 | dynamical dynamical |
Veillet et ali (2002) Grundy, Noll, Stephens (2005) | |
| 2001 QC298 | cubewano (binary) | 6.1 | 244±55* | 0.025±0.011 (R) | dynamical | Grundy, Noll, Stephens (2005) | |
| 2003 EL61 | other TNO (triple) | 0.1 | 1380±56 | 0.663±0.063 | lightcurve/ dynamical |
Rabinowitz et ali (2005) | |
| 2003 QY90 | cubewano (binary) | 6.3 | [201#] | 0.13±0.09 | dynamical | Kern, Elliot (2006) | |
| 2003 UB313 | SDO (binary) | -1.2 | <3310 3000±400 2400±100 | >0.44 0.60±0.15 0.86±0.07 | thermal thermal imaging |
Brown et ali (2006) Bertoldi et ali (2006) Brown et ali (2006) | |
Notes: For binary TNOs, diameter figures with * are for primary only; diameter figures with # are effective combined diameter for both components. Some reported albedos are for red (R), blue (B), or visible/yellow (V) filters; if unspecified, albedo is geometric visual albedo (or is unspecified by source). Some figures by Grundy, Noll, Stephens (2005) are reanalyses of previous results. Figures in brackets are my estimates based on tabulated data. For sources with *, data is from preliminary unpublished results and may have been superceded.
Methods include: eclipses (analysis of mutual eclipses and occultations of primary and secondary), imaging (direct imaging of disk), occultation (stellar occultation), thermal (thermal infrared or radiometric combined with visual photometry), photometric (derived from modeled spectral photometry), dynamical (fit based on observed brightness, dynamics of primary and secondary, and assumed density), and lightcurve/dynamical (fit based on observed lightcurve, derived rotational properties, and dynamics of primary and secondary).
For more information see: