Mutual orbits and masses of six transneptunian binaries

Abstract We present Hubble Space Telescope observations of six binary transneptunian systems: 2000 QL 251 , 2003 TJ 58 , 2001 XR 254 , 1999 OJ 4 , (134860) 2000 OJ 67 , and 2004 PB 108 . The mutual orbits of these systems are found to have periods ranging from 22 to 137 days, semimajor axes ranging from 2360 to 10500 km, and eccentricities ranging from 0.09 to 0.55. These orbital parameters enable estimation of system masses ranging from 0.2 to 9.7 × 10 18 kg . For reasonable assumptions of bulk density (0.5 to 2.0 g cm −3 ), the masses can be combined with visible photometry to constrain sizes and albedos. The resulting albedos are consistent with an emerging picture of the dynamically “Cold” Classical sub-population having relatively high albedos, compared with comparably-sized objects on more dynamically excited orbits.