Abstract:
Fluvial landforms of the Martian southern hemisphere indicate once flowing water on the surface of Mars. Consequently, planetary scientists often describe this early period on Mars as 'warm and wet' and the current period as 'cold and dry'. However, despite its crucial role in biological and geological processes, information about water on Mars is still controversial. We (Usui and my collaborators at Tokyo Tech, NASA's Johnson Space Center and Carnegie Institute of Washington) have reported on geochemical studies that help resolve this controversy that surrounds the origin, abundance, and history of water on Mars (Usui et al. 2012, 2015, Kurokawa et al. 2014, in press). The team revealed the micro-distribution of hydrogen isotopes recorded in Martian meteorites; hydrogen is the major component of water and it isotopes (H and Deuterium) are good indicators to trace the history of water. We reported convincing evidence: (1) the Martian mantle has retained a primordial hydrogen isotope composition similar to water on Earth but distinct from the water in the present Martian atmosphere (D/H = ~5-6 times Earth's ocean water), (2) subsurface water-ice (D/H = ~2-3 times Earth's ocean water) should currently exist, and (3) the buried cryosphere accounts for a large part of the initial water budget of Mars. In my talk, I will also discuss how international collaboration on future Mars robotic missions will explore unknown subsurface environments and potential habitability questions.