Extended Data Fig. 4: VIRTIS water-ice analysis plots.
From: The Philae lander reveals low-strength primitive ice inside cometary boulders
a, b, Average radiance factor of the skull-top boulder location (blue curve) and of the nearby dark terrain (red curve) before (a) and after (b) normalization at 550 nm. c, Theoretical abundance of water ice as a function of the spectral slope in the visible (VIS) spectral channel44. Black dots and dashed lines indicate a water-ice-rich region observed by VIRTIS to calibrate the theoretical curves. The black line represents a solely areal mixing case and the red line a solely intimate mixing case. The blue and green lines represent a merge of both, with different mixing ratios of 1 and 10, respectively. The x-axis values correspond to slope values scaled to the dark terrain unit viewing conditions (Fig. 3b, panel b1, red box) for observation V1_00424522185.QUB.
