Abstract Fans, landforms that record the storage and transport of sediment from uplands to depositional basins, are found on Saturn’s moon Titan, a body of significantly different process rates and material compositions from Earth. Images obtained by the Cassini spacecraft’s synthetic aperture radar reveal morphologies, roughness, textural patterns and other properties consistent with fan analogues on Earth also viewed by synthetic aperture radar. The observed fan characteristics on Titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometres, exposing topographic variations and influences on fan formation. There is evidence for a range of particle sizes across proximal to distal fan regions, from c. 2 cm or more to fine-grained, which can provide details on sedimentary processes. Some features are best described as alluvial fans, which implies their proximity to high-relief source areas, while others are more likely to be fluvial fans, drawing from larger catchment areas and frequently characterized by more prolonged runoff events. The presence of fans corroborates the vast liquid storage capacity of the atmosphere and the resultant episodic behaviour. Fans join the growing list of landforms on Titan derived from atmospheric and fluvial processes similar to those on Earth, strengthening comparisons between these two planetary bodies.

Discoveries in geobiology have dramatically shaped our understanding of the nature, distribution, and evolutionary potential of terrestrial life, paving the way for new exploration strategies to search for life elsewhere in the Solar System. Genomic studies, applied over a broad range of geological environments, have revealed that the vast proportion of species on Earth are microbial. Studies of the fossil record indicate that this has been the case for >75% of our planet's history. Microbial life has been shown to occupy a stunning array of environmental extremes, seemingly only limited by the distribution of liquid water and its chemical activity, nutrient availability, suitable energy sources, radiation, etc. Advances in geomicrobiology have revealed important contributions of microbial processes to many global biogeochemical cycles, and in the evolution of Earth's atmospheric and surface composition. The discovery of a subsurface biosphere, fueled by inorganic chemical energy and able to tolerate extremes in temperature and salinity, has been especially important in opening up new horizons for the astrobiological exploration of Mars, as well as icy satellites of the outer Solar System. Although the environment of life's origin remains uncertain, molecular studies suggest that the last common ancestor of life probably lived in hydrothermal environments where it utilized simple compounds of carbon, hydrogen, and sulfur as sources of chemical energy. This general view is consistent with what we know about late Hadean to early Archean environments on the Earth, as well as model-based interpretations of late, giant impacts that could have exterminated early mesophilic (and possibly photosynthetic) surface life forms, leaving behind only deep subsurface chemotrophic thermophilic microbial communities to re-populate the biosphere. These and related discoveries have contributed extensively to the view that life could be much more broadly distributed, within the Solar System and beyond, than once thought. We now believe it possible that life may have become established in surface environments on Mars during the first half billion years of the planet's history, when liquid water was widespread there. Furthermore, a subsurface hydrosphere on Mars (suggested by both models and geomorphic evidence) may have provided a continuously habitable zone for life over most of Martian history and could still support an active, deep biosphere on Mars today. Exploration of the outer Solar System supports the presence of saline brines (perhaps oceans) beneath the icy crusts of Europa, Callisto, and possibly Ganymede, along with plausible energy sources for life based on chemical disequilibria between oxidized and reduced compounds. It also appears that interior zones of liquid water may also exist on Enceladus, a moon of Saturn, while hydrocarbon oceans of liquid methane discovered on Titan may provide alternative solvents for novel life forms completely unlike anything found on Earth. Ongoing efforts to systematically explore potentially habitable environments elsewhere in our Solar System have helped catalyze the development of astrobiology, an emerging interdisciplinary science that seeks to understand the origin, evolution, distribution, and future of life in the cosmos. Geobiology, which studies interactions of biological and physical-chemical systems and how they have evolved over the history of Earth, is a central focus of astrobiology, providing fertile ground for the growth of conceptual models and new technological tools needed to implement the search for extraterrestrial life elsewhere in the Solar System.

Abstract This publcation is a comprehensive and integrated review of energy and mineral resources in the Solar System, including materials that can both sustain future manned expeditions and colonies in space and support Earth's energy and critical material challenges in the 21st century and beyond. All long-range programs for human exploration and settlement of the solar system recognize the vital role that extraterrestrial energy and mineral resources must play in support of human habitation of near Earth Space and the Moon, Mars, and the Asteroids. Produced in colaboration with the AAPG Energy Minerals Division and the AAPG Astrogeology Committee, this Memoir reflects AAPG's vision of advancing the science and technology of energy, minerals, and hydrocarbon resources into the future and supporting exploration and development of the ultimate frontier, beyond Earth's atmosphere.

The Big Island of Hawai‘i presents ample opportunities for young planetary volcanologists to gain firsthand field experience in the analysis of analogs to landforms seen on Mercury, Venus, the Moon, Mars, and Io. In this contribution, we focus on a subset of the specific features that are included in the planetary volcanology field workshops described in the previous chapter in this volume. In particular, we discuss how remote-sensing data and field localities in Hawai‘i can help a planetary geologist to gain expertise in the analysis of lava flows and lava flow fields, to understand the best sensor for a specific application, to recognize the ways in which different data sets can be used synergistically for remote interpretations of lava flows, and to gain a deeper appreciation for the spatial scale of features that might be imaged in the planetary context.

Central pit craters are common on ice-rich bodies, such as Mars, Ganymede, and Callisto. Mars and Ganymede represent the two end members regarding target characteristics (mixed ice and soil for Mars vs. almost pure ice for Ganymede). Comparisons of central pit craters on these two bodies can provide insights into the environmental conditions under which these craters form and provide constraints on the proposed formation models. This analysis includes 1604 central pit craters on Mars and 471 central pit craters on Ganymede. Martian central pit craters are divided into floor pits and summit pits, whereas all central pit craters on Ganymede are floor pits. Central pit craters form in similar-diameter ranges on both Mars and Ganymede when gravity differences are considered, and both bodies show no regional variations in pit crater distribution within the ±60° latitude zone. Martian floor pits are larger relative to their parent crater than summit pits, but the Ganymede pit/crater diameter ratio is larger than for either central pit type on Mars. Central pits have formed over the entire history of both bodies, and there is no indication that excavation depths have varied over time. Lack of crater floor updoming in Martian floor pit craters indicates that low concentrations of ice (estimated at ~20%) still allow production of central pits. The results of this study argue against central peak collapse as the formation mechanism for central pit craters. Excavation into a subsurface liquid layer cannot be ruled out but is difficult to support based on the distributions and consistencies in excavation depth on both bodies. These results support the model of vaporization and gas escape for central pit formation on both Mars and Ganymede.