(47171) 1999 TC36 - Physical Characteristics

Physical Characteristics

(47171) 1999 TC₃₆ is a triple system consisting of a central primary, which is itself a binary, and a small moon (component B). The combined observations by the infrared Spitzer Space Telescope, Herschel Space Telescope and the Hubble Space Telescope (HST) make it possible to estimate the sizes of the components and consequently provide the range of possible values for the objects’ bulk density. The single-body diameter (effective system size) of 1999 TC₃₆ is currently estimated at 393.1+25.2
−26.8 km.

The very low estimated density of 0.3–0.8 g/cm3 obtained in 2006 (when the system was thought to be a binary) would require an unusually high porosity of 50–75%, assuming an equal mixture of rock and ice. The direct measurement of visible fluxes of all three components of the system in 2009 by the HST has resulted in an improved average density of 0.532+0.317
−211 g/cm3 confirming the earlier conclusion that the object is probably a rubble pile. The density was revised up to 0.64+0.15
−0.11 g/cm3 in 2012 when new information from the Herschel became available. For a bulk density in the range 1–2 g/cm3 the porosity is in the range 36–68%, again confirming that the object is a ruble pile.

1999 TC₃₆ has a very red spectral slope in visible light and a flat spectrum in near infrared. There is also a weak absorption feature near the wavelength of 2 μm, probably caused by water-ice. The best model reproducing the near infrared spectrum includes tholins, crystalline water ice, and serpentine as surface materials. These results are for the integrated spectrum of all three components of the system.