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Enceladus and Europa, icy moons of Saturn and Jupiter, respectively, are believed to be habitable with liquid water oceans and therefore are of interest for future life detection missions and mission concepts. With the limited data from missions to these moons, many studies have sought to better constrain these conditions. With these constraints, researchers have, based on modeling and experimental studies, hypothesized a number of possible metabolisms that could exist on Europa and Enceladus if these worlds host life. The most often hypothesized metabolisms are methanogenesis for Enceladus and methane oxidation/sulfate reduction on Europa. Here, we outline, review, and compare the best estimated conditions of each moon's ocean. We then discuss the hypothetical metabolisms that have been suggested to be present on these moons, based on laboratory studies and Earth analogs. We also detail different detection methods that could be used to detect these hypothetical metabolic reactions and make recommendations for future research and considerations for future missions.

Abstract Astrobiology-related laptop-delivered 360-degree immersive Virtual Field Trips (VFTs) are increasingly used in higher education. However, the literature remains sparse on the experiences in approach to pedagogy and what works and what does not in attaining the intended outcomes. Part of the reason for that has been the limitation on the cost of making this educationally promising type of VFT in terms of time and money, but various initiatives are addressing these two limiting factors. Thus, the pedagogical aspects underpinning making this type of VFT remain largely unexplored. We experimented with the 360-degree VFTs for an astrobiological field site that attracts global researcher interest-the Pilbara Craton of Western Australia, where the world's best preserved and most convincing evidence of early life on Earth exists, from 3.48 billion years ago. Our challenge was to engage final-year undergraduate science students-with little to no geology background-with this field site without visiting it, because of the remote location, safety considerations, and cost. Another consideration was that the astrobiology course in which the VFT resides is fully online, so students not currently residing in Australia can enroll, adding to practical logistical problems for field work. We present our experiences over six years of data in which one pedagogical change stood out above all others-introducing a handwritten field notebook for a VFT-suggesting that it is a key pedagogical consideration for field-related VFTs.

Active hot springs are dynamic geobiologically active environments. Heat- and element-enriched fluids form hot spring sinter deposits that are inhabited by microbial and macroscopic eukaryotic communities, but it is unclear how variable heat, fluid circulation, and mineralization within hot spring systems affect the preservation of organic matter in sinters. We present geological, petrographic, and organic geochemical data from fossilized hot spring sinters (<13 Ka) from three distinct hot spring fields of Yellowstone National Park. The aims of this study were to examine the preservation of hydrocarbons and discern whether the hydrocarbons in these samples were derived from in situ communities or transported by hydrothermal fluids. Organic geochemistry reveals the presence of n -alkanes, methylalkanes, hopanes, and other terpanes, and the distribution of methylheptadecanes is compared to published observations of community composition in extant hot springs with similar geochemistry. Unexpectedly, hopanes have a thermally mature signal, and Raman spectroscopy confirms that the kerogen in some samples has nearly reached the oil window, despite never having been buried. Our results suggest that organic matter maturation occurred through below-surface processes in the hotter, deeper parts of the hydrothermal system and that this exogenous material was then transported and emplaced within the sinter.

The Perseverance rover (Mars 2020) is equipped with an instrumental and analytical payload capable of identifying a broad range of organic molecules in geological samples. To determine the efficacy of these analytical techniques in recognizing important ecological and environmental signals in the rock record, this study utilized analogous equipment, including gas chromatography/mass spectrometry, Raman spectroscopy, X-ray fluorescence (XRF), Fourier transform infrared spectroscopy, along with macroscopic and petrographic observations, to examine early-middle Cambrian microbialites from the Arrowie Basin, South Australia. Morphological and petrographic observations of these carbonate successions reveal evidence of hypersaline-restricted environments. Microbialites have undergone moderate diagenesis, as supported by XRF data that show mineral assemblages, including celestine and the illitization of smectite. Raman spectral data, carbon preference indices of ∼1, and the methylphenanthrene index place the samples in the prehnite/pumpellyite metamorphic facies. Pristane and phytane are the only biomarkers that were detected in the least thermally mature samples. This research demonstrates a multitechnique approach that can yield significant geological, depositional, paleobiological, and diagenetic information that has important implications for planning future astrobiological exploration.

Hot spring environments are commonly dominated by silica sinters that precipitate by the rapid cooling of silica-saturated fluids and the activity of microbial communities. However, the potential for preservation of organic traces of life in silica sinters back through time is not well understood. This is important for the exploration of early life on Earth and possibly Mars. Most previous studies have focused on physical preservation in samples <900 years old, with only a few focused on organic biomarkers. In this study, we investigate the organic geochemistry of hot spring samples from El Tatio, Chile and the Taupo Volcanic Zone, with ages varying from modern to ∼9.4 ka. Results show that all samples contain opaline silica and contain hydrocarbons that are indicative of a cyanobacterial origin. A ∼3 ka recrystallized, quartz-bearing sample also contains traces of cyanobacterial biomarkers. No aromatic compounds were detected in a ∼9.4 ka opal-A sample or in a modern sinter breccia sample. All other samples contain naphthalene, with one sample also containing other polyaromatic hydrocarbons. These aromatic hydrocarbons have a thermally mature distribution that is perhaps reflective of geothermal fluids migrating from deep, rather than surface, reservoirs. These data show that hot spring sinters can preserve biomolecules from the local microbial community, and that crystallinity rather than age may be the determining factor in their preservation. This research provides support for the exploration for biomolecules in opaline silica deposits on Mars.