The criteria for a habitable world initially was based on Earth and centered around liquid water on the surface, warmed by a Sun-like star. The moons of the outer Solar System, principally Europa and Enceladus, have demonstrated that liquid water can exist below the surface warmed by tidal forces from a giant planet. Titan demonstrates that surface liquids other than water - liquid methane/ethane - may be common on other worlds. In this presentation, McKay will discuss the expanding criteria for a habitable world. Taking into consideration the numerous extrasolar planets so far discovered and the prospect of discovering extrasolar moons, McKay believes it is timely to reconsider the possibilities for habitability in the Solar System and on extrasolar planets and moons, and how scientists determine the attributes and search methods for detecting habitable worlds and evidence of life. Brief Bio - Chris is a research scientist with the NASA Ames Research Center. His research focuses on planetary science and the origin of life. He is also actively involved in planning for future Mars missions including human exploration. Chris been involved in research in Mars-like environments on Earth, traveling to the Antarctic dry valleys, Siberia, the Canadian Arctic, the Atacama, Namib, & Sahara deserts to study life in these Mars-like environments. He was a co-investigator on the Huygens probe to Saturn’s moon Titan in 2005, the Mars Phoenix lander mission in 2008, and the Mars Science Laboratory mission, launched in 2012.