Opposition slope for Set 1 with respect to the mean phase angle. We adopted Criterion 3 (e.g., no i and e limitation). The wavelengths of the bands become longer counterclockwise from the top left. Gray dots present S_OE for each pixel, and open circles with vertical error bars show the median values and the standard deviations of each pixel in the 0.°05 bin of the phase angle. We fit the median values at smaller and larger phase angles with lines (see the Sect. 3).