English: Aden Crater is one of Potrillo’s shield volcanoes, formed by a series of effusive eruptions that ended about 16,000 years ago. The lava seeped out over time, and the flows stacked on top of each other, creating a gently sloping cone. The crater became famous in the late 1920s after a fossilized ground sloth, later determined to be about 11,000 years old, was discovered in a lava tube along the crater rim. The presence of pits and lava tubes is the reason that the RIS4E team chose to work at Aden. Lava tubes on other planets could preserve unique rock types and environmental conditions, and perhaps even pristine samples that would be ideal for scientific study. In addition, lava tubes could be used to protect future astronauts, their food, and hardware from radiation and harsh environments. RIS4E was designed to address how to determine which holes in the ground are just pits, which might lead to safer environments, and which ones can be safely explored.