NASA's chief scientist Ellen Stofan announced that she has left the space agency. The reason? She says she is leaving NASA for "new adventures." Ellen Stofan left NASA this month after serving as chief scientist since August 2013. Agency spokesman Dwayne Brown was not immediately able to provide an exact departure date, or plans to select a new chief scientist. Stofan's departure was noted by NASA publicly only in an interview the agency posted on its Tumblr social media account Dec. 21. In the interview, NASA said Stofan was "departing for new adventures," but was not more specific.