(Proposal ID) S13B-134

(PI) Terai, Tsuyoshi

(Proposal Title)
Photometric Diagnosis of Water Ice Abundance on Trans-Neptunian Objects

(Abstract)
Near-infrared spectroscopy for trans-neptunian objects (TNOs) shows that 1000 
km-scale objects are covered by water ice, while objects with diameter less 
than 500 km appear to have ice-poor surfaces. In the transitional size range 
from 500 to 900 km in diameter, most objects have small fractions of water ice 
on the surfaces, though significant water ice absorptions are detected in a 
few objects. The depth of absorptions of water ice at 1.5 and 2.0 micron 
implies the presence of fresh ice on the surface that is likely to have been 
provided from the interior due to cryovolcanic activity. More detailed studies 
of the relationship between surface water ice abundance and object size as 
well as surface colors provide insights into the internal structure, thermal 
evolution, and formation region of TNOs. We propose a near-infrared narrow-
band photometry for intermediate-size TNOs using MOIRCS. The Ks-NB2071 color 
allows to measure the intensity of 2.0-micron absorption of water ice more 
precisely and efficiently than spectroscopy.