Just over two years http://www.ucheducationcentre.org/starscape-time-slots/ starscape time slots  "Crafting the science and exploration goals is a crucial milestone in preparing for our next major Mars mission," said John Grunsfeld, NASA's associate administrator for science. "The objectives determined by NASA, with the input from this team, will become the basis later this year for soliciting proposals to provide instruments to be part of the science payload on this exciting step in Mars exploration."