Planetary surfaces

Abstract:

Laboratory spectral analysis of well-characterized meteorite samples can be employed to more quantitatively analyze asteroid remote sensing data in conjunction with returned extraterrestrial samples. In this work, we examine the combined effects of physical (temperature, particle size) and chemical (petrologic type, metal fraction) variables on visible and near-infrared (VNIR) spectra of ordinary chondrite meteorite powders. Six equilibrated ordinary chondrite meteorite falls were prepared at a variety of particle sizes to capture the spectral diversity associated with asteroid regoliths dominated by various grain sizes. Mineral compositions and abundance were determined from electron microprobe analysis of meteorite thick sections to precisely characterize changes in spectral features due to variations in mineralogy. VNIR spectra of the ordinary chondrites were measured under simulated asteroid surface conditions at a series of temperatures chosen to mimic near-Earth asteroid surfaces. The resulting spectra show minimal variation in both major absorption bands across the simulated near-Earth asteroid temperature regime. Changes in particle size result in variations in band centers and band area ratios for material of the same composition, two key parameters typically used to derive asteroid composition. Unlike previous spectral investigations of ordinary chondrites, we retained the metal fraction in our powders instead of analyzing only the silicate fraction. Metal has a subtle but non-negligible effect on the VNIR spectra of ordinary chondrites. The more petrologically pristine samples from each ordinary chondrite group display relatively weaker absorption bands than their more thermally altered counterparts. The band centers shift to longer wavelengths as grain size and petrologic type increase.

Abstract:

The Lunar Trailblazer smallsat mission High-resolution Volatiles and Minerals Moon Mapper (HVM³) science instrument was designed to acquire targeted spectral image cubes of the lunar surface at visible to shortwave infrared (VSWIR) wavelengths (0.6–3.6 μm) in an effort to understand the distribution, abundance, and form (OH, H2O, ice) of lunar water, as well as the lunar water cycle. The Lunar Trailblazer mission end was declared in July 2025. Here, we describe the formulation and testing of VSWIR spectral parameters in preparation for previously anticipated returned data from HVM³ using global image cubes and mosaic data from the Moon Mineralogy Mapper (M³) imaging spectrometer, HVM³'s predecessor, and the Deep Impact spacecraft. We expand upon the existing M³ global spectral parameter library, test the efficacy of presented parameters individually and alongside existing M³ spectral parameters, provide examples of quantitative thresholds intended to indicate robust mineral detections, and discuss the spectral parameter limitations. We demonstrate that newly formulated and existing parameters capture lunar mineral diversity well and serve as a reliable indicator of lunar surface hydration, making them useful for existing and future scientific analysis using lunar orbital remote sensing data sets.

Abstract:

Abstract Ultra-short period lava worlds offer a unique window into the coupled evolution of planetary interior and atmospheres under extreme irradiation. In this study, we investigate the mantle dynamics, nightside volcanism, and volatile outgassing on lava world K2-141 b (1.54 R⊕, 5.31 M⊕) using two-dimensional convection models with tracer-based volatile tracking. Our simulations explore a range of interior configurations, including models with and without plastic yielding, basal versus mixed heating, core cooling, and melt intrusion. In models without plastic yielding (i.e. with a strong lithosphere), we find that mantle upwellings form at the substellar and antistellar points, while downwellings form near the day-night terminators at the boundary between the magma ocean and cold, solid nightside. These downwellings facilitate the recycling of crustal material, representing a form of asymmetric, single-lid tectonics. The resulting magma ocean thickness varies from 200 to 300 km depending on the model parameters, corresponding to about 2-3 % of the planet’s radius. Continuous nightside volcanism produces a basaltic crust and gradually depletes the mantle of volatiles. We find that over a billion years, volcanic eruptions can outgas tens of bars of CO2 and H2O. We show that even relatively large volcanic eruptions on the nightside produce thermal emission signals of no more than 1 ppm, remaining below the current detectability threshold in thermal phase curves. However, for most models, outgassing rates are increased near the day-night terminators and future studies should assess whether such localised outgassing could lead to atmospheric signatures in transmission spectroscopy.

Abstract:

Abstract Hot and moist “hothouse” climates occurred in Earth's past and are expected in Earth's far future climate, driven by increasing solar luminosity. In hothouse climate regimes, precipitation transitions from a quasi‐steady state, as in present‐day tropical convection, to an “episodic deluge” or relaxation‐oscillator (RO) regime where precipitation occurs in intense bursts separated by multi‐day dry spells. Recent studies suggest that the transition to RO convection regimes is radiatively driven. However, the transition from steady state to RO convection has only been studied with radiative convective equilibrium (RCE) simulations with constant insolation, excluding the diurnal cycle. Precipitation and convection are strongly linked to the diurnal cycle in Earth's present climate over both land and ocean. We explore the impact of the diurnal cycle on the transition from steady state to RO convection using two sets of small‐domain RCE simulations with ocean and swamp‐like surface boundary conditions. Our RCE simulations with ocean boundary conditions show convection transitions to an episodic deluge regime at 322 K and the diurnal cycle modulates precipitation to occur during late‐night or near dawn, when convective inhibition is the weakest. Our RCE simulations with swamp‐like boundary conditions, which allow for mean surface temperature variations, show that as RO states emerge, the diurnal cycle modulates precipitation to primarily occur during the late‐afternoon to about dusk; but as the mean SST increases, precipitation occurs during the late‐night to dawn. These results show that the diurnal cycle strongly influences the timing of convection and precipitation patterns in extreme climates.

Abstract:

The spectrum of an exoplanet reveals the physical, chemical, and biological processes that have shaped its history and govern its future. However, observations of exoplanet spectra are complicated by the overwhelming glare of their host stars. Here, we focus on high-resolution spectroscopy (HRS) (R∼5,000−140,000$$R\,{\sim }\,5{,}000-140{,}000$$), which helps disentangle and isolate the exoplanet’s spectrum. HRS resolves molecular features into a dense forest of individual lines in a pattern that is unique for a given molecule. For close-in planets, the spectral lines undergo large Doppler shifts during the planet’s orbit, while the host star and Earth’s spectral features remain essentially stationary, enabling a velocity separation of the planet. For slower-moving, wide-orbit planets, HRS, aided by high contrast imaging, instead isolates their spectra using their spatial separation (high contrast spectroscopy; HCS). The planet’s spectral lines are compared with HRS model atmospheric spectra, typically using cross-correlation to sum their signals. It is essentially a form of fingerprinting for exoplanet atmospheres and works for both transiting and non-transiting planets. It measures their orbital velocity, true mass, and simultaneously characterizes their atmosphere. The unique sensitivity of HRS to the depth, shape, and position of the planet’s spectral lines allows it to measure atmospheric composition, structure, clouds, and dynamics, including day-to-night winds and equatorial jets, plus its rotation period and even its magnetic field. These are extracted using statistically robust log-likelihood frameworks and match space-based instruments in their precision. This chapter describes the HRS technique in detail and concludes with future prospects with Extremely Large Telescopes to identify biosignatures on nearby rocky worlds and map features in the atmospheres of giant exoplanets.