Fig. S8: Geomorphological analysis of gullies on the central peak of Lyot Crater, Mars

THEMIS temperature values on the central peak (red line and red frequency bars). Black dots are TES high temperature and pressure values. The yellow box represents the range of temperatures and pressures recorded in Lyot. CO<sub>2</sub> and H<sub>2</sub>O phase lines show that present-day THEMIS temperatures enable water to remain in the solid state (although liquid is the next potential phase before vapour), and for carbon dioxide to remain in the vapour state, and so we would not expect to see solid frost on the peak of Lyot. THEMIS data, however, are lacking during the night in winter; slightly lower temperatures than those we observe today would allow for temporary solid-state frost on the surface. Data correspond with main text Figure 18a plot.