Solar system

Abstract:

Survive or not survive, that is the question of the 500-hour JWST Rocky Worlds DDT Program. Whether a terrestrial planets’ atmosphere can suffer under the intense XUV of its host, or if it completely escapes, these are the questions we explore. Zahnle & Catling (2017) defined the Cosmic Shoreline, but recent observations from JWST reveal airless worlds around M-stars, calling for a refinement of this “receding” shoreline (Pass et al. 2025). M-stars spend a longer time in pre-main sequence, subjecting their orbiting worlds to some higher intensity XUV activity. This complicates our present understanding of this shoreline. Investigating chemical effects of planet-star interactions could be the key to a more complete picture of this shoreline.  We investigate the interplay between photochemistry, mixing, and escape of carbon dioxide atmospheres under intense and mild XUV fluxes as follow on work to both Johnstone et al. (2018) and Nakayama et al. (2022). We expand on this work by adopting thermal structure models from Nakayama et al. (2022) and apply them to identify key chemical pathways for escape. We create a reduced C-O chemical network including neutral and ionic species to identify these pathways. As photochemistry simulations take into account many reactions, these 1D calculations are too computationally expensive to be done in 3D. Although rudimentary at best, the mixing parameter– eddy diffusion term, K_zz, comprises the dynamical element of 1D photochemical simulations. Here, we consider the mixing of photochemical products in competition with escape to explore the chemical pathways of retention and loss. We compare the photochemical model results for active and inactive cases for the Trappist-1 system planets. Then, using the resulting composition-dependent heating and cooling rates for Trappist-1 planets, we assess their propensity for efficient atomic line cooling versus escape. We follow the work of Chatterjee & Pierrehumbert (2024) in this assessment.  Finally, using our pathway analysis, we find an analytical formula for calculating an energy-limited escape boundary for these planets based on composition.  It is important here to note the limitations of 1D work. First, there exists an exchange of rigor between modelling chemistry and dynamics. Insights from this work are ripe for implementation into 3D GCMs, especially in response to incorporating UV-driven processes for thermospheric modelling mentioned in Ding and Wordsworth (2019). Second, interaction with the interior is important in the early phase of planetary formation, i.e., the magma ocean phase. Due to exchange between atmosphere and magma early in the planet’s formation, incorporation with an interior-atmosphere model would better constrain higher pressure chemical abundances. Although this work focuses on the upper atmosphere, extrapolation to the surface environment is a key goal for understanding a planet.  Considering planet-star interaction is imperative for the selection of targets for observation. However, it is also important when considering anomalous detections of atmospheres around planets predicted to not have an atmosphere. This could be a first step in determining an atmosphere as non-primary and/or distinguishing between an airless planet and one with high altitude haze. 

Abstract:

NASA’s Lucy mission [1] successfully completed a flyby encounter with the main-belt asteroid (52246) Donaldjohanson on April 20, 2025, collecting data as part of a full-scale operational test for Lucy’s future Trojan encounters.  Donaldjohanson was known to be a C-type asteroid and based on our ground-based observations, to have a Fe-bearing phyllosilicate 0.7 µm absorption. Similar absorptions in spectra of CI, CM, and CR carbonaceous chondrites are indicative of aqueously altered mafic silicates [2-4]. Donaldjohanson is also a member of the 155 Mya Erigone family [5], which is dominated by objects that have also been inferred to be aqueously altered based on their visible 0.7 µm absorptions [6].The Multi-spectral Visible Imaging Camera (MVIC), part of Lucy’s L’Ralph instrument [7-8], was specifically designed to include a filter covering the 0.7 µm absorption to detect evidence of aqueous alteration on the mission’s primary Trojan targets. The Donaldjohanson encounter is thus an excellent opportunity to compare the performance and calibration of MVIC to ground-based data. Here, we will report on both these validation efforts and our exploration of the spatial variability of the 0.7 µm phyllosilicate absorption across the imaged surface of Donaldjohanson to understand potential variability with surface features and photometry, and in relation to other Erigone family objects.References: [1] Levison et al. (2021) PSJ. [2] Cloutis et al. (2011a) Icarus. [3] Cloutis et al. (2011b) Icarus. [4] Cloutis et al. (2012) Icarus. [5] Marchi et al., (2025) PSJ. [6] Morate, D., et al. (2016) A&A. [5] Reuter et al. (2023), SSR. [6] Simon, A.A., et al. 2025 PSJ.Acknowledgments: The Lucy mission is funded through the NASA Discovery Program (Contract No. NNM16AA08C).

Abstract:

Introduction: The surfaces of airless bodies, such as asteroid (101955) Bennu, are typically composed of a regolith mixture containing both coarse and fine particulates. Observations from NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission demonstrated a discontinuity between the remote sensing derived thermophysical properties and thermal spectroscopy results, indicating that a fine layer of dust may be coating the large boulders and coarse regolith surface [1]. To better understand the impact of such a coating on the thermal infrared spectra measured at Bennu, this work developed experimental methods for simulating dust coverings using Space Resource Technology’s CI simulant, based on the bulk composition of the Orgueil meteorite [2].    Figure 1: FTIR Reflectance Spectra of Control Samples of CI simulant. Figure 2: Figure 2: Microscope Camera Images of Sample Surfaces (7%, 10%, 15%, 20%, 25%, 50% Fines wt) of CI simulant Methods: The CI simulant was first sieved into seven size fractions: 1000 mm. An unsieved sample was used as a control. The spectra of the eight samples were measured using a Bruker Vertex 70v Fourier Transform Infrared Reflectance (FTIR) spectrometer, normalized using a gold standard prior to and after measurements, in the range of 1000-650 cm-1 (Figure 1). The dust coating was simulated by placing increasing mass fractions of fine particulates (10% change in the spectral slope).  Implications for OSIRIS-Rex Findings: From the data returned by the OSIRIS-Rex Thermal Emission Spectrometer (OTES) [3],  thermal inertia modelling imply that the surface is porous;, however, the spectral findings indicate that the surface is composed of non-porous? rocks with thin dust coatings [4]. Our experiments find that as little as ~7 wt % of 7% wt) was sufficient to overwhelm and dominate mid-infrared emissivity spectra. The results indicate that the discontinuity in OTES data could be linked back to dust coating on the larger rocks and boulders.   References: [1] Tinker C. et al. (2023) RAS Techniques and Instruments (Vol. 2, Issue 1). [2] Landsman Z. et al. (2020) EPSC 2020. [3] Christensen P. R. et al. (2018) Space Science Reviews (Vol. 214, Issue 5). [4] Rozitis B. et al. (2022) JGR: Planets (Vol. 127, Issue 6). [5] Rivera-Hernandez F. et al. (2015) Icarus (Vol. 262). 

Abstract:

Introduction: On the 20th of April 2025, NASA’s Lucy mission [1] flew by the C-type main-belt asteroid (52246) Donaldjohanson (hereafter DJ). The encounter’s goal was to test the spacecraft and instruments during an observation sequence commensurate with those to be used on Lucy’s main targets – Jupiter’s Trojan asteroids. Data returned from the panchromatic Lucy LOng Range Reconnaissance Imager (L’LORRI, 450-850 nm, [2]) during this testing sequence reveal the asteroid to be bi-lobed and elongated shape (Fig. 1).DJ is a member of the Erigone collisional family, named after the parent body asteroid (163) Erigone (see references in [3]). Ground-based color observations (Fig. 2) show it to decrease in color towards shorter wavelengths, possibly due to the presence of hydrated materials [4].In this work, we present an analysis of color images taken by Lucy’s Multispectral Visible Imaging Camera (MVIC). MVIC consists of six time delay integration (TDI) charge-coupled devices (CCDs). TDI works by synchronizing the transfer rate of the image between CCD rows and the relative motion of the instrument allowing a high signal to noise image to be built up even for fast scans. It covers wavelengths between 375 nm and 950 nm using five color filters and a panchromatic one (see Table 1).Color Analysis: We focus our analysis on images acquired with the four wide band filters: violet, green, orange and near-IR. Our results will provide resolved color variations and contextualise DJ’s color with respect to ground-based observations of DJ, Erigone (Fig. 2), other members of the Erigone family, and the broader asteroid and small body populations.Filter Wavelength Violet 375-480 Green 480-520 Orange 520-625 Phyllosilicate 625-750 Near-IR 750-950 Panchromatic 350-950 Table 1 – MVIC filters [5]Figure 1 – (52246) Donaldjohanson as seen by the panchromatic Lucy L’LORRI instrument, taken on April 20, 2025 at 17:51 UTC.  Figure 2 – Ground-based normalized (at 0.55 µm) visible spectrum of DJ (blue) acquired with the Gran Telescopio Canarias compared to the Bus-DeMeo’s Cg-type (black) and the mean spectrum of the C-type members within the Erigone family (grey). Taken from [6]. Acknowledgments: The Lucy mission is funded through the NASA Discovery program on contract No. NNM16AA08C.References: [1] Levison et al. (2021) PSJ 2, 171. [2] Weaver et al. (2023), SSR 219, 82. [3] Marchi et al., (2025) PSJ 6, 59. [4] Vilas (1995) Icarus 115, 217-218. [5] Reuter et al. (2023), SSR 219, 69. [6] Souza-Feliciano et al. (2020), Icarus 338, 113463.

Abstract:

Clouds are the manifestations of atmospheric dynamics, chemistry, thermal evolution, and orbital characteristics; thus, understanding their physical and spectral properties and their spatial and temporal variability is critical to understanding the planet as a whole.  Observations of Saturn by the Hubble Space Telescope since 1994 and by Cassini from 2004 - 2017 have spanned almost one Saturn year (29.5 Earth years).  Despite the wealth of data, a self-consistent picture of the seasonal variations in Saturn’s haze and cloud structure remain elusive. In this work, we present a radiative transfer analysis of Cassini-VIMS (Visible and Infrared Mapping Spectrometer) spectra in order to derive the vertical structure and color properties of Saturn’s clouds and their latitudinal and seasonal variability.  VIMS records spectra over visible (0.3 to 1.05 micron) and infrared (0.85 to 5.1 micron) channels at spectral resolutions of 7 and 16 nm, respectively.  After a review of the VIMS dataset, we have identified dayside spectra that capture unique cloud features in a given latitude circle at multiple emission angles, allowing for improved vertical discrimination of cloud models. Data are additionally available over multiple epochs, allowing us to analyze any seasonal evolution.  Using the NEMESIS radiative transfer code (Irwin et al., 2008, JQSRT 109, 1136-1150), we invert the VIMS spectra to derive the vertical profiles of phosphine (PH3), ammonia (NH3) and the vertical structure of 4 haze/cloud layers (using the cloud model and cloud/gas parameters shown in Figure 1).  In preliminary findings, in adopting the chromophore optical constants derived by Sromovsky et al., 2021 (Icarus 362, 114409) for a north polar cloud observed in 2016, we find we can adequately fit the spectra for a subset of clouds observed in September 2014.  At other locations/times, the chromophore optical constants derived by Sromovsly et al., 2021, need to be varied in order to fit the spectra within uncertainty, which indicates seasonal evolution of Saturn’s chromophore.  In this work, we present derived cloud properties and the optical constants of the derived chromophore as a function of latitude and season in order to shed light on the complex interplay between cloud structure, color, chemistry, and orbital characteristics.