Encyclopedia of the Solar System 2nd ed

610 Encyclopedia of the Solar System

TABLE 2 KBO Magnitudes, Albedos, and Diameters^1

Name Number Prov Des V^2 H^3 v p^4 v D^5

Triton 13.5 − 1. 2 75 2707

Eris 136199 2003 UB 313 18.7 − 1. 1 > 70 < 2600

Pluto 134340 14.0 − 0. 7 61 2290

136472 2005 FY 9 17.0 0.1 70–90 1250–1650

Charon 15.9 37 1242

136108 2003 EL 61 17.5 0.4 55–75 1000–1600

Sedna 90377 2003 VB 12 21.1 1.20 >8.5 < 1800

Orcus 90482 2004 DW 19.3 2.3 27 1000

Quaoar 50000 2002 LM 60 19.2 2.7 12 1300

55637 2002 UX 25 19.9 3.6 10 900

55565 2002 AW 197 20.2 3.6 12 734

90568 2004 GV 9 19.8 3.7 15 700

Varuna 20000 2000WR 106 20.1 3.9 14 586

Ixion 28978 2001 KX 76 19.9 4.0 19 480

Huya 38628 2000 EB 173 19.5 5.1 6.6 500

47171 1999 TC 36 19.6 5.4 7.9 405

15874 1996 TL 66 20.9 5.5 >1.8 < 958

15789 1993 SC 22.4 7.3 3.5 398

15875 1996 TP 66 21.1 7.4 1.1 406

29981 1999 TD 10 21.1 9.1 5.3 88

(^1) Courtesy John Stansberry.
(^2) V-band magnitude.
(^3) Absolute magnitude in V-band.
(^4) Visual Albedo in units of percentage from Spitzer Space Telescope and ISO observations.
(^5) Diameter in km from Spitzer Space Telescope and ISO observations
FIGURE 5 (a) The rotation of a non-spherical KBO or Centaur
object results in a periodic variation of the object’s projected area
on the plane of the sky and hence a periodic variation in its
brightness. (b) Brightness vs. time (lightcurve) for the rotation of
a non-spherical object. During one rotation of the object, it goes
through two maxima (points A and C) and two minima (points B
and D) in brightness. (Courtesy of Ron Redsteer and NAU Bilby
Research Center)
8.1 Period of Rotation
If we can determine the form of the periodic brightness vari-
ation (lightcurve) for a KBO or Centaur, they can determine
its period of rotation. Figure 6 shows a plot of V magnitude
vs. time in hours for the Centaur Pholus. At the time of ob-
servation in 2003, Pholus was∼18 AU from the Sun, nearly
the same distance as Uranus. We see that the two maxima
are of nearly equal brightness, but one minimum (at∼5 hr)
is∼0.03 magnitude (3%) fainter than the other minimum
(at 0 hr). The pattern of two maxima and two minima re-
peats every 9.980±0.002 hr, Pholus’ period of rotation on
its axis.
Determining the period of rotation for a KBO or Cen-
taur takes a significant amount of telescope time. In the
case of Pholus, each of the 99 points in Figure 6 represents
a brightness measurement from a 300 sec CCD image. Be-
cause of their faintness, measurements of KBO and Cen-
taurlightcurvesrequire telescopes with moderately large
apertures, typically with diameters≥2 m. A large amount
of time on moderate-size telescopes is difficult to obtain,
so periods of rotations are available for only a handful of
objects (Table 3). Groups led by William Romanishin of the