Chemolithoautotrophic bacteria flourish at dark water-ice interfaces of an emerged Arctic cold seep.

Below their ice shells, icy moons may offer a source of chemical energy that could support microbial life in the absence of light. In the Arctic, past and present glacial retreat leads to isostatic uplift of sediments through which cold and methane-saturated groundwater travels. This fluid reaches the surface and freezes as hill-shaped icings during winter, producing dark ice-water interfaces above water ponds containing chemical energy sources.

Investigating the stability of aromatic carboxylic acids in hydrated magnesium sulfate under UV irradiation to assist detection of organics on Mars.

The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument onboard the Mars 2020 Perseverance rover detected so far some of the most intense fluorescence signals in association with sulfates analyzing abraded patches of rocks at Jezero crater, Mars. To assess the plausibility of an organic origin of these signals, it is key to understand if organics can survive exposure to ambient Martian UV after exposure by the Perseverance abrasion tool and prior to analysis by SHERLOC. In this work, we investigated the stability of organo-sulfate assemblages under Martian-like UV irradiation and we observed that the spectroscopic features of phthalic and mellitic acid embedded into hydrated magnesium sulfate do not change for UV exposures corresponding to at least 48 Martian sols and, thus, should still be detectable in fluorescence when the SHERLOC analysis takes place, thanks to the photoprotective properties of magnesium sulfate.

Spectral evidence for irradiated halite on Mars.

The proposed chloride salt-bearing deposits on Mars have an enigmatic composition due to the absence of distinct spectral absorptions for the unique mineral at all wavelengths investigated. We report on analyses of remote visible-wavelength spectroscopic observations that exhibit properties indicative of the mineral halite (NaCl) when irradiated. Visible spectra of halite are generally featureless, but when irradiated by high-energy particles they develop readily-identifiable spectral alterations in the form of color centers.

Investigating Europa's Habitability with the Europa Clipper.

The habitability of Europa is a property within a system, which is driven by a multitude of physical and chemical processes and is defined by many interdependent parameters, so that its full characterization requires collaborative investigation. To explore Europa as an integrated system to yield a complete picture of its habitability, the Europa Clipper mission has three primary science objectives: (1) characterize the ice shell and ocean including their heterogeneity, properties, and the nature of surface-ice-ocean exchange; (2) characterize Europa's composition including any non-ice materials on the surface and in the atmosphere, and any carbon-containing compounds; and (3) characterize Europa's geology including surface features and localities of high science interest. The mission will also address several cross-cutting science topics including the search for any current or recent activity in the form of thermal anomalies and plumes, performing geodetic and radiation measurements, and assessing high-resolution, co-located observations at select sites to provide reconnaissance for a potential future landed mission.

Sodium chloride on the surface of Europa.

The potential habitability of Europa's subsurface ocean depends on its chemical composition, which may be reflected in that of Europa's geologically young surface. Investigations using Galileo Near-Infrared Mapping Spectrometer data led to the prevailing view that Europa's endogenous units are rich in sulfate salts. However, recent ground-based infrared observations have suggested that, while regions experiencing sulfur radiolysis may contain sulfate salts, Europa's more pristine endogenous material may reflect a chloride-dominated composition.

Distinct Microbial Assemblage Structure and Archaeal Diversity in Sediments of Arctic Thermokarst Lakes Differing in Methane Sources.

Developing a microbial ecological understanding of Arctic thermokarst lake sediments in a geochemical context is an essential first step toward comprehending the contributions of these systems to greenhouse gas emissions, and understanding how they may shift as a result of long term changes in climate. In light of this, we set out to study microbial diversity and structure in sediments from four shallow thermokarst lakes in the Arctic Coastal Plain of Alaska. Sediments from one of these lakes (Sukok) emit methane (CH) of thermogenic origin, as expected for an area with natural gas reserves.

The Possible Emergence of Life and Differentiation of a Shallow Biosphere on Irradiated Icy Worlds: The Example of Europa.

Irradiated ice-covered ocean worlds with rocky mafic mantles may provide the conditions needed to drive the emergence and maintenance of life. Alkaline hydrothermal springs-relieving the geophysical, thermal, and chemical disequilibria between oceans and tidally stressed crusts-could generate inorganic barriers to the otherwise uncontrolled and kinetically disfavored oxidation of hydrothermal hydrogen and methane. Ionic gradients imposed across these inorganic barriers, comprising iron oxyhydroxides and sulfides, could drive the hydrogenation of carbon dioxide and the oxidation of methane through thermodynamically favorable metabolic pathways leading to early life-forms.

Energy, chemical disequilibrium, and geological constraints on Europa.

Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa.

Clathrate hydrates of oxidants in the ice shell of Europa.

Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes.