Supporting material for Science paper press release

Authors: Shane Byrne and Andrew Ingersoll

Fig. 1. High resolution view of a typical depression in the polar CO2 ice ('Swiss-cheese depression'). All the salient features of the Swiss cheese features are visible here, including steep walls, flat floors, indications of some collapse around the walls and a slight asymmetry in the north-south direction. Just below and to the right is a slight depression which may be the progenitor of a future Swiss-cheese feature. The 'elephant hide' appearance of the surrounding terrain is commonly observed near these features. In this and subsequent figures arrows denote the direction to the sun (*) and north (N). Sub-frame of MOC narrow angle image M09/00609, taken at 87o S, 353o E, Ls 237o.

Fig. 2. Many Swiss cheese features destroying the upper 8m thick layer. All the features displayed here have a consistent orientation, with their asymmetric 'cusps' pointing toward the pole. This is a strong indication that insolation has played a dominant role in their formation. The consistency in size indicates these features started forming close in time to each other compared with their overall lifetimes. Sub-frame of MOC narrow angle image M07/04167, taken at 86.8o S, 355o E, Ls 211o.

Fig. 3. Layers visible in the walls of the Swiss-cheese. In some places only two main layers can be seen (A), other locations show up to 15 closely spaced layers (B). A) Sub-frame of MOC narrow angle image M12/00161, taken at 86.8o S, 12o E, Ls 294o. B) Sub-frame of MOC narrow angle image M12/01995, taken at 86.9o S, 17o E, Ls 305o.

Fig. 4. Example of Swiss-cheese observed by THEMIS in the top panel (I01162002) near the cap center at 86.5o S, 75o W, Ls 345o. The temperature ranges from ~150 (blue) to ~160 Kelvin (red). The MOC narrow angle image in the bottom panel (E05/02715) shows that the warm areas correspond to the floors of the depressions near the walls. These warm areas cannot be CO2 ice.

THEMIS infrared data is available at Arizona State University
MOC narrow angle image data is available at Malin Space Science Systems