Planetary surfaces

Abstract:

We describe the capabilities, radiometric stability, and calibration of a custom vacuum environment chamber capable of simulating the near-surface conditions of airless bodies. Here we demonstrate the collection of spectral measurements of a suite of fine particulate asteroid analogs made using the Planetary Analogue Surface Chamber for Asteroid and Lunar Environments (PASCALE) under conditions like those found on Earth and on airless bodies. The sample suite includes anhydrous and hydrated physical mixtures, and chondritic meteorites (CM, CI, CV, CR, and L5) previously characterized under Earth- and asteroid-like conditions. And for the first time, we measure the terrestrial and extra-terrestrial mineral end members used in the olivine- and phyllosilicate-dominated physical mixtures under the same conditions as the mixtures and meteorites allowing us better understand how minerals combine spectrally when mixed intimately. Our measurements highlight the sensitivity of thermal infrared emissivity spectra to small amounts of low albedo materials and the composition of the sample materials. As the albedo of the sample decreases, we observe smaller differences between Earth- and asteroid-like spectra, which results from a reduced thermal gradient in the upper hundreds of microns in the sample. These spectral measurements can be compared to thermal infrared emissivity spectra of asteroid (101955) Bennu's surface in regions where similarly fine particulate materials may be observed to infer surface compositions.

Abstract:

Carbon monoxide (CO) is the main product of CO2 photolysis in the Martian atmosphere. Production of CO is balanced by its loss reaction with OH, which recycles CO into CO2. CO is therefore a sensitive tracer of the OH-catalysed chemistry that contributes to the stability of CO2 in the atmosphere of Mars. To date, CO has been measured only in terms of vertically integrated column abundances, and the upper atmosphere, where CO is produced, is largely unconstrained by observations. Here we report vertical profiles of CO from 10 to 120 km, and from a broad range of latitudes, inferred from the Atmospheric Chemistry Suite on board the ExoMars Trace Gas Orbiter. At solar longitudes 164–190°, we observe an equatorial CO mixing ratio of ~1,000 ppmv (10–80 km), increasing towards the polar regions to more than 3,000 ppmv under the influence of downward transport of CO from the upper atmosphere, providing a view of the Hadley cell circulation at Mars’s equinox. Observations also cover the 2018 global dust storm, during which we observe a prominent depletion in the CO mixing ratio up to 100 km. This is indicative of increased CO oxidation in a context of unusually large high-altitude water vapour, boosting OH abundance.

Abstract:

Geochemical and astronomical evidence demonstrates that planet formation occurred in two spatially and temporally separated reservoirs. The origin of this dichotomy is unknown. We use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. Migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermochemistry, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets.

Abstract:

Spectral data created as part of a study into the effects of aqueous and thermal alteration on the spectral signature in the NIR and MIR wavelength ranges. NIR data were collected as reflectance and MIR data were collected as emissivity under both ambient and simulated asteroid environment (SAE) conditions.