Images taken by THEMIS show what is possibly an opening to a Martian underground cave. [A] is a combined visual and infrared shot of the cave entrance during the day. [B] is an afternoon infrared image. [C] is an early morning infrared image. Credit: GE Cushing, TN Titus, JJ Wynne, USGS, USGS, Northern Arizona University, and PR Christensen of Arizona State University
