[1] We introduce a new technique derived from the classical Stokes parameters for analysis of polarimetric radar astronomical data. This decomposition is based on m (the degree of polarization) and chi (the Poincaré ellipticity parameter). Analysis of the crater Byrgius A demonstrates how m-chi can more easily differentiate materials within ejecta deposits and their relative thicknesses. We use Goldschmidt crater to demonstrate how m-chi can differentiate coherent deposits of water ice. Goldschmidt crater floor is found to be consistent with single bounce Bragg scattering suggesting the absence of water ice and further corroborating adsorbed H to mineral grains or an H 2 O frost as plausible explanations for a H 2 O/OH detection by near-infrared instruments.

Enceladus’s long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around Saturn or Enceladus) and from the moon’s surface. In preparation for the National Academies of Sciences, Engineering and Medicine 2023–2032 Planetary Science and Astrobiology Decadal Survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at Enceladus: Is the subsurface ocean inhabited? Why, or why not? Trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. The team found that Orbilander, a mission concept that would first orbit and then land on Enceladus, represented the best balance. Orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. The Orbilander mission concept demonstrates that scientifically compelling but resource-conscious Flagship-class missions can be executed in the next decade to search for life at Enceladus.

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The theory of plate tectonics describes how a planet's lithosphere is divided into a global network of multiple rigid blocks (plates) that move relative to each other, accommodating deformation primarily in narrow zones around the edges of the plates. Earth is the only planetary body known to operate under a plate tectonic system. Other terrestrial planets lack fully developed, present day plate tectonics, though Venus may demonstrate localized subduction-like behavior (Davaille et al., 2017) and Mars may have experienced plate tectonic-like behavior in its early history (e.g., Nimmo & Stevenson, 2000). Analyses of plate-like motions on Jupiter's moon Europa have provided insight into the formation and evolution of specific feature types and provided a means of testing processes and assumptions based on terrestrial plate tectonics (Schenk & McKinnon, 1989). The sequential reconstruction of Europa's surface in northern Falga Regio by Kattenhorn and Prockter (2014) raised the possibility of a full plate tectonic system operating on Europa. If true, Europa would be the only known world besides Earth to have plate tectonics. This result is of interest for studies of comparative planetology, and raises questions