Distribution of the reflectance ratios of T types as a function of semi-major axes. The ratios of the reflectances measured at 0.8 µm and 0.5 µm (R_0.8/R_0.5) and at 3.2 µm and 2.9 µm (R_3.2/R_2.9) are shown in panels a and b, respectively. Circles with thick black edges denote asteroids whose diameter is greater than 80 km, and circles without edges mark smaller ones (<50 km). Stars represent five T types in near-Earth orbits: (85490) 1997 SE5, (138911) 2001 AE2, (162998) 2001 SK162, 2001 UU92, and 2001 YE1. The horizontal line in panel a denotes the R_0.8 /R_0.5 of the mean reflectance of D types (DeMeo et al. 2009; Fig. 1).