Characterization of Regolith And Trace Economic Resources (CRATER): An Orbitrap-based laser desorption mass spectrometry instrument for in situ exploration of the Moon.

RATIONALE: Characterization of Regolith And Trace Economic Resources (CRATER), an Orbitrap™-based laser desorption mass spectrometry instrument designed to conduct high-precision, spatially resolved analyses of planetary materials, is capable of answering outstanding science questions about the Moon's formation and the subsequent processes that have modified its (sub)surface. METHODS: Here, we describe the baseline design of the CRATER flight model, which requires <20 000 cm3  volume, <10 kg mass, and <60 W peak power. The analytical capabilities and performance metrics of a prototype that meets the full functionality of the flight model are demonstrated. RESULTS: The instrument comprises a high-power, solid-state, pulsed ultraviolet (213 nm) laser source to ablate the surface of the lunar sample, a custom ion optical interface to accelerate and collimate the ions produced at the ablation site, and an Orbitrap mass analyzer capable of discriminating competing isobars via ultrahigh mass resolution and high mass accuracy. The CRATER instrument can measure elemental and isotopic abundances and characterize the organic content of lunar surface samples, as well as identify economically valuable resources for future exploration. CONCLUSION: An engineering test unit of the flight model is currently in development to serve as a pathfinder for near-term mission opportunities.

High-molecular-weight organic matter in the particles of comet 67P/Churyumov-Gerasimenko.

The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley. Such matter is generally thought to have originated in the interstellar medium, but it might have formed in the solar nebula-the cloud of gas and dust that was left over after the Sun formed. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization. Many gaseous organic molecules, however, have been observed; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov-Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites' parent bodies. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.

Comet 67P/Churyumov-Gerasimenko sheds dust coat accumulated over the past four years.

Comets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer. The presence of water-ice grains in periodic comets is now well established. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion. Micrometre-sized interplanetary dust particles collected in the Earth's stratosphere and certain micrometeorites are assumed to be of cometary origin. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices. At its previous recurrence (orbital period 6.5 years), the comet's dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun.

Composition of cometary particles collected during two periods of the Rosetta mission: multivariate evaluation of mass spectral data.

The instrument COSIMA (COmetary Secondary Ion Mass Analyzer) onboard of the European Space Agency mission Rosetta collected and analyzed dust particles in the neighborhood of comet 67P/Churyumov-Gerasimenko. The chemical composition of the particle surfaces was characterized by time-of-flight secondary ion mass spectrometry. A set of 2213 spectra has been selected, and relative abundances for CH-containing positive ions as well as positive elemental ions define a set of multivariate data with nine variables. Evaluation by complementary chemometric techniques shows different compositions of sample groups collected during two periods of the mission. The first period was August to November 2014 (far from the Sun); the second period was January 2015 to February 2016 (nearer to the Sun). The applied data evaluation methods consider the compositional nature of the mass spectral data and comprise robust principal component analysis as well as classification with discriminant partial least squares regression, k-nearest neighbor search, and random forest decision trees. The results indicate a high importance of the relative abundances of the secondary ions C+ and Fe+ for the group separation and demonstrate an enhanced content of carbon-containing substances in samples collected in the period with smaller distances to the Sun.

Detection of Short Peptides as Putative Biosignatures of Psychrophiles via Laser Desorption Mass Spectrometry.

Studies of psychrophilic life on Earth provide chemical clues as to how extraterrestrial life could maintain viability in cryogenic environments. If living systems in ocean worlds (e.g., Enceladus) share a similar set of 3-mer and 4-mer peptides to the psychrophile Colwellia psychrerythraea on Earth, spaceflight technologies and analytical methods need to be developed to detect and sequence these putative biosignatures. We demonstrate that laser desorption mass spectrometry, as implemented by the CORALS spaceflight prototype instrument, enables the detection of protonated peptides, their dimers, and metal adducts. The addition of silicon nanoparticles promotes the ionization efficiency, improves mass resolving power and mass accuracies via reduction of metastable decay, and facilitates peptide de novo sequencing. The CORALS instrument, which integrates a pulsed UV laser source and an Orbitrap™ mass analyzer capable of ultrahigh mass resolving powers and mass accuracies, represents an emerging technology for planetary exploration and a pathfinder for advanced technique development for astrobiological objectives. Teaser: Current spaceflight prototype instrument proposed to visit ocean worlds can detect and sequence peptides that are found enriched in at least one strain of microbe surviving in subzero icy brines via silicon nanoparticle-assisted laser desorption analysis.

Mechanical and electrostatic experiments with dust particles collected in the inner coma of comet 67P by COSIMA onboard Rosetta.

The in situ cometary dust particle instrument COSIMA (COmetary Secondary Ion Mass Analyser) onboard ESA's Rosetta mission has collected about 31 000 dust particles in the inner coma of comet 67P/Churyumov-Gerasimenko since August 2014. The particles are identified by optical microscope imaging and analysed by time-of-flight secondary ion mass spectrometry. After dust particle collection by low speed impact on metal targets, the collected particle morphology points towards four families of cometary dust particles. COSIMA is an in situ laboratory that operates remotely controlled next to the comet nucleus. The particles can be further manipulated within the instrument by mechanical and electrostatic means after their collection by impact. The particles are stored above 0°C in the instrument and the experiments are carried out on the refractory, ice-free matter of the captured cometary dust particles. An interesting particle morphology class, the compact particles, is not fragmented on impact. One of these particles was mechanically pressed and thereby crushed into large fragments. The particles are good electrical insulators and transform into rubble pile agglomerates by the application of an energetic indium ion beam during the secondary ion mass spectrometry analysis.This article is part of the themed issue 'Cometary science after Rosetta'.