Laser Ablation Ionization Mass Spectrometry: A Space Prototype System for In Situ Sulphur Isotope Fractionation Analysis on Planetary Surfaces

The signatures of element isotope fractionation can be used for the indirect identification of extant or extinct life on planetary surfaces or their moons. Element isotope fractionation signatures are very robust against the harsh environmental conditions, such as temperature or irradiation, which typically prevail on solar system bodies. Sulphur is a key element for life as we know it and bacteria exist, such as sulphur reducing bacteria, that can metabolize sulphur resulting in isotope fractionations of up to −70‰ δ34S. Geochemical processes are observed to fractionate up to values of −20‰ δ34S hence, fractionation exceeding that value might be highly indicative for the presence of life. However, the detection of sulphur element isotope fractionation in situ, under the assumption that life has existed or still does exist, is extremely challenging. To date, no instrument developed for space application showed the necessary detection sensitivity or measurement methodology for such an identification. In this contribution, we report a simple measurement protocol for the accurate detection of sulphur fractionation δ34S using our prototype laser ablation ionization mass spectrometer system designed for in situ space exploration missions. The protocol was elaborated based on measurements of five sulphur containing species that were sampled at different Mars analogue field sites, including two cave systems in Romania and the Río Tinto river environment in Spain. Optimising the laser pulse energy of our laser ablation ionization mass spectrometer (LIMS) allowed the identification of a peak-like trend of the 34S/32S ratio, where the maximum, compared to internal standards, allowed to derive isotope fractionation with an estimated δ34S accuracy of ∼2‰. This accuracy is sufficiently precise to differentiate between abiotic and biotic signatures, of which the latter, induced by, e.g., sulphate-reducing microorganism, may fractionate sulphur isotopes by more than −70‰ δ34S. Our miniature LIMS system, including the discussed measurement protocol, is simple and can be applied for life detection on extra-terrestrial surfaces, e.g., Mars or the icy moons like Europa.

Supplemental Material: Formation of low-gradient bedrock chutes by dry rockfall on planetary surfaces

Supplemental Figures S1–S8, Videos S1–S3, and Data files S1–S8.

Supplemental Material: Formation of low-gradient bedrock chutes by dry rockfall on planetary surfaces

Supplemental Figures S1–S8, Videos S1–S3, and Data files S1–S8.

Interaction bounding surfaces exposed in migrating transverse aeolian ridges on Mars

Wind-blown sand self-organizes into bedforms that have now been identified on six different planetary bodies. These bedforms, including ripples and dunes, exhibit patterns that are diagnostic of surface-atmosphere interactions and can be used to interpret winds and sediment supply from satellite images of planetary surfaces. Patterns in dune and ripple fields change when one or more bedforms interact, for example, by linking, colliding, or merging with one another. When two bedforms interact, the cross-strata developed by the bedforms include a bounding surface where the two bedforms combined. These “interaction bounding surfaces” have been interpreted from ancient and modern strata in recent literature, but they have not yet been identified beyond Earth. On Mars, aeolian dunes and ripples form much as they do on Earth, but additional enigmatic bedform types are also present. Transverse aeolian ridges are straight-crested bedforms found abundantly on Mars, but with few analogs on Earth. Formation mechanisms for these enigmatic bedforms range from dune-like migration and construction to growth in place via wedge stacking or kinetic sieving. In this work, I studied exposed stoss-slope stratification on these enigmatic Martian bedforms to (1) identify the first in situ examples of interaction bounding surfaces captured visually, and (2) demonstrate that the transverse aeolian ridges must have been forward migrating.

Rampart craters on Earth

ABSTRACT Rampart craters are omnipresent features on volatile-rich solid planetary surfaces. This raises the question whether, and how many, rampart craters are present on Earth. We reviewed the terrestrial impact crater record with regard to possible rampart morphologies and present detailed morphological analyses of these terrestrial craters here. Our results show that the Ries crater in Germany, Bosumtwi crater in Ghana, Tenoumer crater in Mauritania, Lonar crater in India, and Meteor crater in the United States are terrestrial rampart craters. The Ries and Bosumtwi craters can be classified as double-layer ejecta (DLE) craters, whereas Tenoumer, Lonar, and Meteor craters can be classified as single-layer ejecta (SLE) craters. Tenoumer and Meteor craters show rampart as well as common lunar-like ejecta characteristics within their ejecta blankets and, thus, appear to be hybrid craters. In addition, we discuss seven crater structures that show at least some morphological or lithological peculiarities that could provide evidence for possible ejecta ramparts. Considering the low number of terrestrial impact craters with well-preserved ejecta blankets, the relatively high proportion of rampart craters is astonishing. Obviously, the formation of layered or rampart craters is a common and not a rare process on Earth.