We measured the thresholds for photodetachment from the first and second excited rotational levels of CH− to the lowest vibrational, rotational, and fine-structure level of CH to be E1 = 1.213 ± 0.002 eV and E2 = 1.206 ± 0.002 eV, respectively. Based on these measurements and the rigid rotor approximation, we arrive at an electron affinity of EA = E1 + 1/2 (E1 − E2 ) = 1.217 ± 0.002 eV. This value deviates from earlier experimental results but agrees with the calculation by Feller [J. Chem. Phys. 144, 014105 (2016)]. In the present experiment, we stored ensembles of initially hot CH− in the cryogenic ion-beam storage ring Double ElectroStatic Ion-Ring ExpEriment (DESIREE) for tens of seconds such that the vast majority of the ions were in the few lowest excited rotational levels of the electronic and vibrational ground state.We identified the initial states for photodetachment channels with threshold energies E1 and E2 by comparing the time dependences of measured photodetachment signals with radiative rotational-cooling rates calculated using the literature values of the dipole moment of CH−. The conditions of a few occupied rotational levels are superior to those of previous studies of this system and an important step toward future studies with an all-rotational-ground-state ion beam.

The gas phase reactivity of the radical cation isomers H₂CNH˙+ (methanimine) and HCNH₂˙+ (aminomethylene) with propene (CH₃CHCH₂) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07–11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation. Experimental results have been merged with theoretical calculations to elucidate reaction pathways and structures of products. The H₂CNH˙+ isomer is over a factor two more reactive than HCNH₂˙+. A major channel from both isomers is production of protonated methanimine CH₂NH₂+via hydrogen-atom transfer reaction but, while H₂CNH˙+ additionally gives charge and proton transfer products, the HCNH₂˙+ isomer leads instead to protonated vinylimine CH₂CHCHNH₂+, produced alongside CH₃˙ radicals. The reactions have astrochemical implications in the build up of chemical complexity in both the interstellar medium and the hydrocarbon-rich atmospheres of planets and satellites.

Interest in the observation and characterization of organic isomers in astronomical environments has grown rapidly with an increase in the sensitivity of detection techniques. Accurate modeling and interpretation of these environments require experimental isomer-specific reactivity and spectroscopic measurements. Given the abundance of formaldehyde (H2CO) in various astrophysical objects, the properties and reactivities of its cation isomers H2CO•+ and HCOH•+ are of significant interest. However, for the hydroxymethylene radical cation HCOH•+ (and its isotopologue DCOH•+), detailed reactivity studies have been limited by the lack of suitable experimental methods to generate this isomer with high purity. Here, potential approaches to the isomer-selective generation of HCOH•+ and DCOH•+ are characterized through differential reactivity measurements. While the dissociative photoionization of cyclopropanol (c-CH2CH2CHOH) is determined to be unsuitable, the dissociation of methanol-d3 (CD3OH) allows for the formation of DCOH•+ with a fractional abundance of >99% at photon energies below 14.8 eV. These results will allow future spectroscopic and reactivity measurements of HCOH•+/DCOH•+ to be conducted, laying the groundwork for future detection and incorporation into models of the interstellar medium.

Studying larger nucleophiles in bimolecular nucleophilic substitution (S_N2) reactions bridges the gap from simple model systems to those relevant to organic chemistry. Therefore, we investigated the reaction dynamics between the methoxy anion (CH₃O⁻) and iodomethane (CH₃I) in our crossed-beam setup combined with velocity map imaging at the four collision energies 0.4, 0.7, 1.2, and 1.6 eV. We find the two ionic products I⁻ and CH₂I⁻, which can be attributed to the S_N2 and proton transfer channels, respectively. The proton transfer channel progresses in a previously observed fashion from indirect to direct scattering with increasing collision energy. Interestingly, the S_N2 channel exhibits direct dynamics already at low collision energies. Both the direct stripping, leading to forward scattering, and the direct rebound mechanism, leading to backward scattering into high angles, are observed.

In the search for evidence of extant or extinct life on Mars, characterization of the physical and geochemical properties of a sample – as well as the physicochemical conditions under which that sample was collected – may be critical in the interpretation of any biosignatures discovered. To ensure collection of a statistically meaningful set of samples for biosignature assessment, multiple samples should be collected in these same locations, as well as in nearby areas of the same material (i.e., similar in physical and geochemical properties). To determine the optimal spatial sampling for such a sample set, we explored four volcanic regions of Iceland: two recent tephra fields (Holuhraun and Fimmvörðuháls) and two older glaciovolcanic sand sheets, or sandur (Dyngjusandur and Mælifellssandur). These regions have a similar mafic rock source but span different time periods and experience geomorphological forces to differing degrees. Such differences can lead to micro-variability in the physical material that make up these Mars analog sites, thus we aimed to characterize the differences in composition and physical aspects of material between and within these four locations. We selected areas that appeared repetitive and homogeneous from visible satellite and uncrewed aerial vehicle (UAV) imagery, and collected samples over a range of spatial scales (10 ​cm–1 ​km). We utilized visible to near-infrared and short-wavelength infrared (VNIR/SWIR) reflectance spectroscopy, X-ray fluorescence (XRF), and measurements of sampled sediment moisture content and grain size to characterize the physical and geochemical properties. VNIR/SWIR spectra contained features consistent with iron-bearing minerals such as pyroxene, basaltic glass and ferric oxides/oxyhydroxides. The two tephra fields had a larger contribution of iron phases compared to the two sandurs, and Holuhraun spectra in particular showed evidence of Fe-bearing glass. Average spectra depicted trends that appear to correlate with location age, including an increase in Fe oxide absorption (0.54 ​μm), a shift of the broad absorption at 1.0 ​μm to shorter wavelengths, an increase in structural and molecular water at 1.4 and 1.9 ​μm, and an increase in the hydroxylated mineral (likely Si–OH) absorption near 2.2 ​μm. The bulk geochemical compositions of the four sites were largely undifferentiable within SiO2, Al2O3, MgO, MnO, Na2O, and TiO2, whereas other elements (K2O, CaO, FeO, and P2O5) showed trends that grouped the two northern sites (Dyngjusandur and Holuhraun) and the two southern sites (Mælifellssandur and Fimmvörðuháls) together. While there were some differences between the four regions studied, statistical analysis of moisture content, grain size, and summary products derived from VNIR/SWIR data indicate comparable variability in sample geochemical and physical properties up to the 10-m scale, and substantially increased variability at the 100-m and 1-km scales, suggesting that current and future missions in search of biosignatures should target separate sampling areas no more than 10 ​m apart for repeat measurements of the same material.

Lava tubes on Mars hold exciting potential for the preservation of biosignatures, which may survive on geological timescales in these isolated, stable environments. To support the development of future astrobiological mission concepts, we turn to terrestrial lava tubes, host to a variety of microbial communities and secondary minerals. Following a multidisciplinary sampling protocol, we retrieved biological, molecular, and mineralogical data from several lava tubes in Iceland. We report on blue-colored copper-rich secondary minerals and their associated bacterial communities using a multi-method approach, and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy data sets. We found numerous bacterial genera known for their high metal resistance and ability to survive in low-nutrient environments. Both are characteristics to be expected for any potential life in Martian lava tubes, and should be considered when checking for contaminants in Mars mission preparations. Associated with the microbial mats, we identified several types of copper-rich secondary minerals, indicating localized copper enrichments in the groundwater, possibly stemming from overlying ash deposits and nearby hyaloclastite formations. Molecular analysis revealed carotenoid signals preserved within the copper speleothems. If found in Martian lava tubes, blue copper-rich mineral precipitates would be deserving of astrobiological investigation, as they have potential to preserve biosignatures and harbor life.

By repeatedly probing the a¹Δ excited state and the X³Σ⁻ ground-state populations in a beam of CH⁻ ions stored in a cryogenic ion-beam storage ring for 100 s, we extract an intrinsic lifetime of 14.9±0.5 s for this excited state. This is far longer than all earlier experimental and theoretical results, exposing large difficulties in measuring and calculating slow decays and the need for benchmark quality experiments.

In response to ESA’s “Voyage 2050” announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn’s largest moon Titan. Titan, a “world with two oceans”, is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan’s remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a “heavy” drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan’s northern latitudes with an orbiter and in situ element(s) would be highly complementary in terms of timing (with possible mission timing overlap), locations, and science goals with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan’s equatorial regions, in the mid-2030s. 

The search for signs of life on Mars and beyond is time consuming and labor-intensive; hence, it is critical to understand how to design sampling strategies that can maximize the likelihood of success. Two distinct Mars analogue environments in Iceland were selected to represent volcanic resurfacing and glacial environments where characterization of different biosignatures at various spatial scales (100 m, 10 m, 1 m, 10 cm) was performed. This study serves the twofold purposes of (1) understanding the different levels of biosignature distributions in these analogue environments and (2) the spatial distributions of biosignatures in these environments, with an overarching goal of drawing lessons from low biomass Mars analogue environments to inform the best sampling strategies for sample collection strategies on Mars. Our results show that samples should be collected for analysis at large (at least 100 m spacing) to capture most differences within an apparently homogeneous environment of the aged resurfaced volcanic region like Mælifellssandur, whereas a smaller spacing at 10 m scale is necessary for younger glacial–volcanic environments like Fimmvörduháls. This study also illustrates the importance of understanding the variability across spatial scales in sampling design for future planetary missions.

The vibrational transitions and the relative abundances of the two isomeric ions H₂CNH⁺ and H₂NCH⁺ generated through electron impact ionisation have been investigated in a noble gas tagging experiment. It could be shown that both species were formed with an abundance of 70 and 30% for H₂NCH⁺ and H₂CNH⁺, respectively. The obtained vibrational bands of the two species have been assigned to vibrational transitions through comparison with the results of ab initio calculations. These computations also predict both species to be moderately polar. The present investigations show that both isomers should be included in chemical model calculations of dark interstellar clouds, protoplanetary disks, star-forming regions as well as planetary atmospheres.