66652 Borasisi, or as a binary (66652) Borasisi-Pabu,^[7] is a binary classical Kuiper belt object. It was discovered in September 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 Space Telescope.

In 2003 it was discovered that 66652 Borasisi is a binary with the components of comparable size (about 100–130 km) orbiting the barycentre on a moderately elliptical orbit.^[6][8] The total system mass is about 3.4 × 10¹⁸ kg.^[7]

The companion (66652) Borasisi I, named Pabu, 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.^[7]

The surface of both components of the Borasisi–Pabu system is very red.^[6]

Borasisi is named after a fictional creation deity taken from the novel Cat's Cradle by Kurt Vonnegut.^[9] In the book, Borasisi is the Sun and Pabu is the name of the Moon:^[10]

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.

Around 2005, Borasisi was considered as a target for the proposed New Horizons 2 after a Triton/Neptune flyby.^[11]