8 Questions Astrobiology: Are We Alone in the Universe? A quiz aligned with the interactive "Stories of Life" learning experiences on #Infiniscope, an SMD project powered by NASA. NASA_Infiniscope, 01/18/2019 answers Play True or False: There is only one planet known for certain to have life. True False Approximately, how many extrasolar planets (outside our solar system) have been discovered? 4 40 400 4,000 What defines a planet as habitable? rocky surface an atmosphere ability to sustain liquid water around a yellow star … and 5 more awesome questions! Check them out by clicking “Play”.