MRO Overview: Sixteen Years in Mars Orbit

The Mars Reconnaissance Orbiter (MRO) entered Mars orbit on March 10, 2006, and as of September 2023 has been in its primary science orbit for 17 years. By the end of its current extended mission in September 2025, MRO observations will have covered a Mars decade (~19 Earth years). As a dual-purpose mission, MRO was launched to pursue a "Follow the Water" science theme and to provide key programmatic support elements for the next missions of NASA’s Mars Exploration Program. The spacecraft has operated 6 science instruments provided by five institutions and supported two additional science investigations which utilized the telemetry from spacecraft accelerometers and tracking. This payload has viewed the surface, atmosphere, and subsurface of Mars with greater spatial resolution and systematic coverage than ever before, revealing a dynamic planet which has changed dramatically over time and which continues to change even now. MRO and other missions have revealed a major transition from a wetter planet to the current cold, drier climate, but the diversity and nature of those water-related environments show that this transition was complex and not a simple "drying" out. Furthermore, those transitions were not confined only to ancient Mars, as MRO observations have shown that water related activity extended into later geologic times as well. MRO’s long record and high spatial resolution have shown that Mars continues to change today under the influence of atmospheric winds and the action of volatile frosts. Whether or not some phenomena, such as the enigmatic recurring slope lineae, are caused by transient development of liquid water is still debated, and the characterization of such phenomena continues to be a focus of observation by MRO. Meanwhile, the frequency and distribution of local and regional dust storms have emerged from the atmospheric data, although the precise triggers for planetary-scale dust events remain elusive. Their impact on modern Mars and on robotic exploration is evident, from changes in the global circulation and atmospheric structure to the enhanced loss of water to space to the eventual demise of solar-powered spacecraft on the Martian surface. Mars has also preserved in its subsurface the physical record of geologically more recent climate change. The finely layered interiors of the polar layered deposits and the detection of buried ice in mid-latitudes, sometimes exposed in icy scarps or in recent impact craters, point to multiple ice ages in recent geologic times. The difference in the structures of the polar caps remains a challenge to theory, and the south polar cap in particular exhibits unexpected features, such as enough buried CO2 ice that, if sublimed into the atmosphere, would double the present atmospheric mass. Also challenging are the patterns of defrosting of the south polar seasonal ice, producing its fan-like depositions of spider-shaped landforms. Finally, there is the ongoing pummeling of the Martian surface, with MRO observing over 2000 new impact craters and using both new and old craters to gain insight into ancient mineral formation and modern ice presence. Despite aging of the orbiter subsystems and payload, the ingenuity and expertise of the MRO teams has sustained spacecraft operations. MRO has the fuel and capability to continue operating for many more productive years of science observation and mission support, although declining budgets have curtailed some science activities, including termination of still useful investigations. Although much knowledge has been gained, there is still much more to learn about Mars using ongoing capabilities and what continued observation can tell us about the history and climate processes of the terrestrial planets, including our own.