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66652 Borasisi

66652 Borasisi
Discovered by A. Trujillo, J. Luu and D. Jewitt
Discovery date September 8, 1999
MPC designation (66652) 1999 RZ253
Minor planet category trans-Neptunian object
Orbital characteristics[4]
Epoch June 18, 2009 (JD 2455000.5)
Aphelion 48.164 AU
Perihelion 39.982 AU
Semi-major axis 44.073 AU
Eccentricity 0.0928
Orbital period 292.60 a (106,871 d)
Mean anomaly 46.593°
Inclination 0.5629°
Longitude of ascending node 84.74°
Argument of perihelion 200.0°
Satellites Pabu
(137 km in diameter?)[3]
Physical characteristics
Dimensions 134–182 km[5]
Mass 3.433 ± 0.027×1018 kg[5]
Albedo 0.10–0.25, assuming density 0.5–2.0 g/cm3[5]
Absolute magnitude (H) 5.86

66652 Borasisi /ˌbɒrəˈssi/ is a binary classical Kuiper belt object. It was discovered in 1999 by Chad Trujillo, Jane X. Luu and David C. Jewitt[4] and identified as a binary in 2003 by K. Noll and colleagues[4] using the Hubble Telescope.


In 2003 it was discovered that 66652 Borasisi is a binary with the components of comparable size (about 120–180 km) orbiting the barycentre on a moderately elliptical orbit.[6] The total system mass is about 3.4 × 1018 kg.[5]

The companion (66652) Borasisi I, named Pabu /ˈpɑːb/ orbits its primary in 46.2888 ± 0.0018 days on an orbit with semi-major axis of 4528 ± 12 km and eccentricity 0.4700 ± 0.0018. The orbit is inclined with respect to the observer by about 54° meaning that is about 35° from the pole-on position.[5]


Borasisi is named after a fictional creation deity taken from the novel Cat's Cradle by Kurt Vonnegut.[7] In the book, Borasisi is the Sun and Pabu is the name of the Moon:[8]

Borasisi, the sun, held Pabu, the moon, in his arms and hoped that Pabu would bear him a fiery child. But poor Pabu gave birth to children that were cold, that did not burn... Then poor Pabu herself was cast away, and she went to live with her favorite child, which was Earth.


External links

  • Orbital simulation from JPL (Java)
  • Ephemeris
  • IAUC 8143

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