(342842) 2008 YB3

, provisional designation:, is a sizable centaur and retrograde damocloid from the outer Solar System, approximately 67 km in diameter. It was discovered on 18 December 2008, by astronomers with the Siding Spring Survey at the Siding Spring Observatory in Australia. The minor planet was numbered in 2012 and has since not been named.

Orbit and classification
 orbits the Sun at a distance of 6.5–16.7 AU once every 39 years and 5 months (14,399 days; semi-major axis of 11.58 AU). Its orbit has an eccentricity of 0.44 and an inclination of 105° with respect to the ecliptic. The body's observation arc begins with its official discovery observation at Siding Spring in December 2008.

Retrograde centaur and damocloid
 is a member of the centaurs, a population of inward-moving bodies transiting from the Kuiper belt to the group of Jupiter-family comets. Orbiting mainly between Jupiter and Neptune, they typically have a semi-major axis of 5.5 to 30.1 AU. Centaurs are cometary-like bodies with an eccentric orbit. Their short dynamical lifetime is due to the perturbing forces exerted on them by the outer planets of the Solar System.

The object is on a retrograde orbit as it has an inclination of more than 90°. There are only about a hundred known retrograde minor planets out of nearly 800,000 observed bodies, and, together with and 2011 MM4, it is among the largest such objects. The object also meets the orbital definition for being a damocloid. This is a small group of cometary-like objects without a coma or tail and a Tisserand's parameter with respect to Jupiter of less than 2 besides a retrograde orbit.

Numbering and naming
This minor planet was numbered by the Minor Planet Center on 29 October 2012, receiving the number in the minor planet catalog  (M.P.C. 80959). , it has not been named. According to the established naming conventions, it will be named after one of the many centaurs from Greek mythology, which are creatures with the upper body of a human and the lower body and legs of a horse.

Physical characteristics
 has an intermediate BR color, in between the BB ("grey-blue") and RR ("very red") color classes. Sheppard's obtained color indices: B–I (1.750), B–R (1.260), R–I (0.490) and V–R (0.460) agree with most other centaurs. The resulting B–V index is 0.8 (subtracting V–R from B–R).

Diameter and albedo
According to the survey of centaurs and scattered-disc objects carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer,  measures 67.1 km in diameter and its surface has an albedo of 0.062, which makes it too small to be considered as a dwarf-planet candidate.

Rotation period
, no rotational lightcurve of has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.