Lambda Paz (also known as Pentarus IIIB) was a moon of Pentarus III. Classified as "barely" class M, its surface was mostly desert with an average temperature of 55° Celsius. It had a very strong magnetic field that could disrupt tricorder and orbital scans.
Picard and Crusher, along with shuttle captain Dirgo, sought shelter in a nearby cave that contained an artificial fountain of water. However, the water was protected by a force field and a sentry that first injured Picard, and then killed Dirgo when they attempted to access the water. Crusher eventually found a way to deactivate the fountain's defenses using a modified tricorder, sustaining Picard's life long enough for them to be rescued by the USS Enterprise-D. (TNG: "Final Mission")