Distribution of spectral slope variation at 2.4 μm in our data set. Pink: nondetection for surface heterogeneity (66 objects). Gray: optimistic candidates (52 objects). Yellow: conservative candidates (12 objects). Since optimistic candidates and noncandidates for surface heterogeneity are not determined using reflectance differences at 2.4 μm, the value of 1 on the abscissa is intentionally left out.