Observations of the trans-Neptunian objects 1993 SC and 1996 TL₆₆ with the Infrared Space Observatory

Observations at 90 μm of the trans-Neptunian objects (TNOs), 1993 SC and 1996 TL₆₆, using the Infrared Space Observatory (ISO) are reported. Five individual observations of 1993 SC were acquired giving a 2.7 σ detection (a confidence level of 99.6%). The signal level of 11.46 ± 4.24 mJy has been modeled using a standard thermal model (STM) and gives an effective radius of 164⁺²⁹_-33 km and a geometric albedo of 0.022^+0.013_-0.006. Estimated radii and albedos using the fast rotator approximation and the thermophysical model are also presented. Two individual observations of 1996 TL₆₆ are also reported. A clear signal of 39.77 ± 11.62 mJy at 90 μm was recorded. However, the position of the signal on the detector does not correspond to the position expected. A detailed investigation has not revealed a satisfactory explanation. Assuming that ISO was mispointed and that the origin of the signal is 1996 TL₆₆, application of the STM gives an effective radius of 316⁺⁴²_-49 km and a geometric albedo of 0.030^+0.012_-0.007. This is in good agreement with expectations based on the assumption that the surfaces of TNOs are similar to those of cometary nuclei. The results for 1996 TL₆₆ and 1993 SC indicate that TNOs are large, spherical, and very dark objects. A main-belt asteroid, 1997 SU₁₅, was also detected giving an effective radius of 1.13 ± 0.04 km and a geometric albedo of 0.25 ± 0.02. An estimate of the relative dependence of the zodiacal light background in the ecliptic on elongation angle at 90 μm was also determined.