Thomas Zurbuchen said other top goals for science and the agency include understanding and protecting life on Earth and probing fundamental aspects of the universe like dark matter and dark energy.
Scientists have found that "super" solar flares could have warmed the ancient planet and jump-started life.
Mineralogist Robert Hazen and other scientists probe connections between living organisms and rocks in "Life's Rocky Start," which premieres tonight on PBS stations around the United States.
The Curiosity rover, one of NASA's flagship missions, analyzes Martian geology, geochemistry, climatology, and radiation to assess whether Mars could have supported microbial life.
Scientists assess the present and past habitability of Mars from organic compounds detected at Gale Crater.