The remote sensing possibilities of orbiters together with their global mapping possibilities allow them to search for an inventory of characteristics of a life habitat on Mars, they permit also a systematic search for the gases that could be indicative of life episodes as well as favourable radiation environments. The current missions are reviewed versus their capability for this objective and ideas are proposed for a specific astrobiology Mars orbiter. Orbiters combine global mapping with the satisfaction of contamination requirements. The recent mapping of dark dune spots and underground ice deposits as well as previous unverified enhancements in atmospheric composition shows possible ways to use orbiters in life detection.