Mars Exploration Rover Project Manager, NASA Jet Propulsion Laboratory
John Callas returns to tell us why, after six years, an end to Spirit's roving does not mean the end of her work on the red planet. Emily Lakdawalla looks to the other side of Mars where Opportunity is rolling up to a baby crater. Bill Nye the Planetary Guy is head over heels for the highest ever skydive. Bruce Betts and Mat Kaplan explain why 'we're number four!' in this week's edition of What's Up, including a new space trivia contest.