Dirk Schulze-Makuch is a professor at the Technical University Berlin, Germany, and an adjunct professor at Arizona State University and Washington State University. He is interested in all aspects of astrobiology, but particularly whether other planets and moons inside and outside our Solar System could serve as a potential habitat for life. He received the Friedrich-Wilhelm Bessel Award from the Humboldt Foundation for extraordinary achievements in theoretical biology  in 2010.  He is best known for his publications on extraterrestrial life, which span nearly 200 scientific articles and several books such as Cosmic Biology: How Life Could Evolve on other Worlds (2011),  Megacatastrophes! Nine Strange Ways the World Could End (2012),  The Extraterrestrial Encyclopedia (2016) and The Cosmic Zoo: Complex Life on Many Worlds (2017), as well as earlier editions of Life in the Universe: Expectations and Constraints (2004and 2008). Louis Irwin is a professor emeritus of biological sciences at the University of Texas at El Paso. He has published close to 100 research papers, reviews, encyclopedia entries, and chapters on neuroscience, astrobiology, and evolution.   He is particularly interested in evolutionary trajectories under different conditions, including those that lead to intelligent and technologically capable forms of life. He has written a neuroscience memoir (Scotophobin, 2006), and co-authored books on evolution (The Evolutionary Imperative, 2016), and astrobiology (Life in the Universe: Expectations and Constraints, 2004 and 2008) and Cosmic Biology: How Life Could Evolve on other Worlds (2011).