Deep-sea hydrothermal vents at mid-ocean ridges are prime analogs for early Earth habitats and potential extraterrestrial biospheres. In 2025, I sailed aboard the R/V Atlantis (AT50-42) to the Endeavor Hydrothermal Vent Field, where our team investigated nitrogen cycling and chemosynthetic microbial communities in vent fluids and sediments. These systems illustrate how life can thrive in the absence of sunlight, powered instead by geochemical energy — a paradigm with implications for the search for life on ocean worlds like Europa and Enceladus.