Abstract

The epic era of our solar system reconnaissance by fearless space probes propelled onto stark hyperbolic trajectories into the unknown has nearly ended with a sparkling evidence and an unforeseen hypothesis: The cryospheres are some of the most common planetary environments in the solar system, and would cryospheres be ideal places to answer whether life is fortuitous or opportunistic?

Icy Worlds, dwarf planets and moons, are dozens. Europa, Ganymede, Enceladus, Titan, Dione, Pluto is a non-exhaustive subset where a liquid water body below the ice crust has been indirectly detected or is reasonably considered. Europa is particular. As some, hypotheses on its structure and activity tend to converge towards the coexistence of conditions that would allow earth-like life to exist. But Europa also likely had a stable planetary and orbital architecture at a billion year scale, a timescale that was sufficient to the emergence of life on early Earth, giving plenty of time for a Europan biosphere to appear and evolve in a relatively peaceful shelter if opportunism is one of its fundamental character.

Although promising, Europa's habitability is still a major hypothesis that needs further testing. To propel science investigations on that matter, the NASA's Europa Clipper mission is scheduled for launch in the early 2020's with a scientific payload of 9 instruments. Among them, the Radar for Europa Assessment and Sounding: Ocean-to-Near Surface (REASON) is a radar sounder led by UTIG at UT Austin. REASON is a multifaceted instrument designed to characterize the distribution of shallow englacial waters, to search for an ice-ocean interface, to investigate vertical material exchange from the ocean to the exosphere, to constrain the amplitude of gravitational tides, and to characterize the surface to support a potential landed mission. REASON's capacity to provide compelling information for the assessment of a habitable environment is demonstrated by the investigation of analog places in the Earth cryosphere.