The Science Case for a Titan Flagship-class Orbiter with Probes

International audienceTitan is one of the most exciting and varied destinations in our solar system. Titan's surface includes seas, lakes, dunes, desiccated river valleys and floodplains, while its atmosphere is replete with multiple layers of haze, clouds and rain, all of which are both reminiscent of Earth and utterly alien in equal measure. A mission to Titan provides a rare opportunity to study terrestrial processes in a completely different regime, and thereby learn about our home planet as we also learn about the wider solar system. Our most direct current view of Titan is from the joint NASA-ESA Cassini-Huygens mission that orbited Saturn from 2004 to 2017, which gave us the first detailed look at its largest moon. Through 127 targeted flybys by the Cassini orbiter, and in situ investigation of the lower atmosphere and surface by the Huygens probe, this long-mysterious world finally emerged from the realm of speculation into an equally enthralling place of scientific investigation.However, the mission raised many more questions about Titan that will require further missions to fully answer. To complement the Dragonfly rotorcraft lander targeted to explore Titan's low latitudes, we propose a combined orbiter and lander mission that would target high-latitude liquid surface environments and map Titan in a holistic way from orbit. An instrumented orbiter would carry 1-2 entry probes to land on Titan's polar seas, giving the first ground-truth data from the only non-terrestrial seas in the solar system, and a truly detailed global picture of Titan's evolving atmosphere and surface.Such a mission strongly addresses NASA's high-level strategic objective in planetary science: to "ascertain the content, origin, and evolution of the solar system and the potential for life elsewhere" (2014 NASA Science Plan), as well as focused goals including: "explore and observe the objects in the solar system to understand how they formed and evolve," and "advance the understanding of how the chemical and physical processes in our solar system operate, interact and evolve." An international collaboration to provide instruments, spacecraft elements or systems similar to the Cassini-Huygens team would share costs, risks and scientific rewards globally