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We provide the first solar system wide compendium of speleogenic processes and products. An examination of 15 solar system bodies revealed that six cave‐forming processes occur beyond Earth including volcanic (cryo and magmatic), fracturing (tectonic and impact melt), dissolution, sublimation, suffusion, and landslides. Although no caves (i.e., confirmed entrances with associated linear passages) have been confirmed, 3,545 SAPs (subsurface access points) have been identified on 11 planetary bodies and the potential for speleogenic processes (and thus SAPs) was observed on an additional four planetary bodies. The bulk of our knowledge on extraterrestrial SAPs is based on global databases for the Moon and Mars, which are bodies for which high‐resolution imagery and other data are available. To further characterize most of the features beyond the Moon and Mars, acquisition (preferably global coverage) and subsequent analysis of high‐resolution imagery will be required. The next few decades hold considerable promise for further identifying and characterizing caves across the solar system. Plain Language Summary: Until the last two decades, the potential for caves beyond Earth was principally theoretical. Today, databases of subsurface access points (SAPs) exist for the Moon and Mars. Across the solar system, 3,545 SAPs have been identified on 11 planetary bodies with speleogenic processes identified on another four bodies. Six cave‐forming processes beyond Earth have been identified; these include volcanic (cryo and magmatic), fracturing (tectonic and impact melt), dissolution, sublimation, suffusion, and landslides. As more orbiter and fly by platforms with high‐resolution instrumentation probe the solar system, our knowledge regarding caves beyond Earth will become more robust—culminating with the robotic and perhaps human exploration of caves on the Moon and Mars. Key Points: Six speleogenic processes have been identified across the solar systemTwo speleogenic processes were documented—which are driven by different fluids than on Earth—cryovolcanism and methane‐based dissolutionAt least 3,545 subsurface access points have been identified on 11 planetary bodies with speleogenic processes observed on an additional four bodies [ABSTRACT FROM AUTHOR]

• Eris' eccentric orbit results in 2 atmospheric regimes: a global atm near perihelion and a local atm near aphelion. • A coupled thermal-transport numerical model to simulate thermal and volatile evolution in the LCSA regime is presented. • Volatile transport by local, collisional, sublimation atms (LCSA), even at solar distances of 100 AU, can be significant. • Uniform collapse of a global, nitrogen atmosphere likely cannot explain Eris' anomalous albedo in the present epoch. • Changes of Eris' albedo or color from nitrogen transport may be observable. Kuiper belt object (KBO) Eris is exceptionally bright with a greater visible geometric albedo than any other known KBO. Its infrared reflectance spectrum is dominated by methane, which should form tholins that darken the surface on timescales much shorter than the age of the Solar System. Thus one or more ongoing processes probably maintain its brightness. Eris is predicted to have a primarily nitrogen atmosphere that is in vapor pressure equilibrium with nitrogen-ice and is collisional (not ballistic). Eris's eccentric orbit is expected to result in two atmospheric regimes: (1) a period near perihelion when the atmosphere is global (analogous to the atmospheres of Mars, Triton, and Pluto) and (2) a period near aphelion when only a local atmosphere exists near the warmest region (analogous to the atmosphere of Io). A numerical model developed to simulate Eris's thermal and volatile evolution in the local atmosphere regime is presented. The model conserves energy, mass, and momentum while maintaining vapor pressure equilibrium. It is adaptable to other local, collisional, sublimation atmospheres, which in addition to Io and Eris, may occur on several volatile-bearing KBOs. The model was applied for a limiting case where Eris is fixed at aphelion and has an initial nitrogen-ice mass everywhere equal to the precipitable column of nitrogen in Pluto's atmosphere during the New Horizons encounter (the resultant mass if the Pluto atmosphere collapsed uniformly onto the surface). The model results indicate that (1) transport of nitrogen in the local, collisional, sublimation atmosphere regime is significant, (2) changes of Eris's albedo or color from nitrogen transport may be observable, and (3) uniform collapse of a global, nitrogen atmosphere likely cannot explain Eris's anomalous albedo in the present epoch. Seasonal volatile transport remains a plausible hypothesis to explain Eris's anomalous albedo and geologic processes that renew Pluto's brightest surfaces, such as convection and glaciation, may also be operating on Eris. [ABSTRACT FROM AUTHOR]

Saturn’s moon Enceladus offers a unique opportunity in the search for life and habitable environments beyond Earth, a key theme of the National Research Council’s 2013–2022 Decadal Survey. A plume of water vapor and ice spews from Enceladus’s south polar region. Cassini data suggest that this plume, sourced by a liquid reservoir beneath the moon’s icy crust, contain organics, salts, and water–rock interaction derivatives. Thus, the ingredients for life as we know it – liquid water, chemistry, and energy sources – are available in Enceladus’s subsurface ocean. We have only to sample the plumes to investigate this hidden ocean environment. We present a New Frontiers class, solar-powered Enceladus orbiter that would take advantage of this opportunity, Testing the Habitability of Enceladus’s Ocean (THEO). Developed by the 2015 Jet Propulsion Laboratory Planetary Science Summer School student participants under the guidance of TeamX, this mission concept includes remote sensing and in situ analyses with a mass spectrometer, a sub-mm radiometer–spectrometer, a camera, and two magnetometers. These instruments were selected to address four key questions for ascertaining the habitability of Enceladus’s ocean within the context of the moon’s geological activity: (1) how are the plumes and ocean connected? (2) are the abiotic conditions of the ocean suitable for habitability? (3) how stable is the ocean environment? (4) is there evidence of biological processes? By taking advantage of the opportunity Enceladus’s plumes offer, THEO represents a viable, solar-powered option for exploring a potentially habitable ocean world of the outer solar system. [ABSTRACT FROM AUTHOR]