Planetary surfaces

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:

On November 1, 2023, NASA’s Lucy spacecraft successfully imaged the Main-Belt asteroid (152830) Dinkinesh and its moon, Selam. Dinkinesh is an S- or Sq-type asteroid with multiple geologic features (i.e., craters, central ridge, and trough) [1].  The Dinkinesh system is complex, with satellite that itself is a contact binary [1]. Broadband visible (0.35-0.95 µm) and near-IR (0.97-3.95 µm) hyperspectral images collected by the L’Ralph instrument showed absorption features near 1-, 2-, and 3-µm [2, 3].  The vibrational absorption between 2.6 and 3.3 µm in asteroid spectra has generally been interpreted as OH and H2O (i.e., hydration). This ~3.0 µm band, has been a crucial tool of characterization to understand the degree of hydration on the surface of asteroids [4]. Detection of hydration or volatile-rich materials on S-type objects is surprising due to the expected high temperature at which these bodies formed in the main-belt and presence of anhydrous silicates. Ground-based facilities have provided crucial detections and insights about the 3.0 µm band on S-type asteroids [5,6], yet much remains unknown about its origin. Dinkinesh’s close approach by Lucy offers a fortuitous opportunity to better understand the hydration of these bodies and assess any spatial variation on the surface that might be related to geologic features. The Lucy L’Ralph Dinkinesh observations can help differentiate the source of hydration. For example, exogenous material (e.g., carbonaceous or cometary material) is expected to appear in discrete areas associated with specific surface features such as craters [7]. Alternatively, solar wind implantation on asteroids occurs when high H+ fluxes doses from the Sun interact with surface minerals, embedding hydrogen atoms and potentially leading to the formation of OH or H2O in the regolith [8]. We will report on the spectral analysis of Dinkinesh, with a focus on the shape model registration of hyperspectral images from the L’Ralph Multi-spectral Visible Imaging Camera (MVIC) and Linear Etalon Imaging Spectral Array (LEISA). We will present colors, spectral slopes, and band depth to look for possible spectral heterogeneities associated with geologic morphologies. Results: We registered the digital shape model of Dinkinesh to the L’Ralph instrument detectors. Figure 1 shows a preliminary example of the MVIC panchromatic filter frame during the close approach registered to the respective incidence angle backplane obtained using SpiceyPy [9]. Figure 2 shows an example of a LEISA-calibrated frame (e.g., I/F) registered to Dinkinesh’s shape model.  After registration, the 3 µm absorption feature is analyzed for each facet by computing the absorption strength (e.g., band depth) and looking for correlations with surface morphologies provided by stereophotogrammetry of L’LORRI images. Similarly, we obtained MVIC color maps and overlayed them on the shape model. Our preliminary analysis suggests a 3 µm detection across the entire imaged surface, showing variabilities in band depth. We will further explore such variability to find its possible relationship with surface morphologies, local color variations, and illumination geometry.Figure 1. MVIC panchromatic frame of Dinkinesh overlayed with the SpiceyPy incidence angle backplane.Figure 2. Left: Dinkinesh shape model with overlayed LEISA cross-track I/F frame 700 during close approach.  [1] Levison, H.F. et al. 2024. A contact binary satellite of the asteroid (152830)Dinkinesh. Nature 629, 1015–1020.[2] Simon, A. et al. 2025. Lucy L'Ralph In-flight Calibration and Results at (152830) Dinkinesh. Planet. Sci. J.  6, 7.[3] Kaplan, H., et al. 2024.  "Multi-spectral imaging observations of asteroid (152830) Dinkinesh by the Lucy Mission." Proceedings of the Lunar and Planetary Science Conference 2024,abstract #1474. Houston, TX: Lunar and Planetary Institute.[4] Rivkin, A. S. et al. 2018. Evidence for OH or H2O on thesurface of 433 Eros and 1036 Ganymed. Icarus 304, 74–82.[5] McGraw, L. E. et al. 2022. 3 μm Spectroscopic Survey of Near-Earth Asteroids. Planet. Sci. J. 3, 243.[6] McAdam, M. et al. 2024. Detection of Hydration on Nominally Anhydrous S-complex Main Belt Asteroids. Planet. Sci. J. 5, 254.[7] De Sanctis, M. C. et al. 2015. Mineralogy of Marcia, the youngest large crater of Vesta: Character and distribution of pyroxenes and hydrated material. Icarus 248, 392–406.[8] Hibbits, C. A., et al., 2011. Thermal stability of water and hydroxyl on the surface of the Moon from temperature-programmed desorption measurements of lunar analog materials. Icarus, 213, 64-72.[9] Annex, A. M., et al., 2020. SpiceyPy: a Pythonic Wrapper for the SPICE Toolkit. Journal of Open Source Software, 46, 2050.

Abstract:

Introduction: During the Reconnaissance phase of NASA’s OSIRIS-REx mission, the Thermal Emission Spectrometer (OTES) acquired high–spatial resolution emissivity spectra over Bennu’s four prospective sampling sites [1, 2]. We analyse the calibrated OTES dataset archived in the Planetary Data System [3] to quantify compositional and mineralogical diversity across the original four candidate sample sites (Nightingale, Kingfisher, Osprey, and Sandpiper) and to explore possible drivers of Bennu’s surface heterogeneity, including implications for Bennu’s mineralogy and space-weathering history.  Figure 1: Site-Averaged Emissivity Spectra with Annotated Band Parameters Methods: Calibrated emissivity spectra (5.7-100 µm) were linked to corresponding OCAMS imagery [5] to place the thermal infrared measurements in geological context, by cross-referencing observation times. For every spectrum we derived four diagnostic band parameters: Christiansen Feature (CF), silicate stretching band, silicate bending band and spectral slope, following the methods outlined in [6]. Each site contains thousands of spectral observations (site-averaged for visualization in Figure 1). The corresponding band parameters were compared using three statistical models: Principal Component Analysis (PCA) [5], k-Nearest Neighbors (KNN) [7], and Analysis of Variance (ANOVA) [8]. The three methods compare the mean and variance of each individual observation per site, considering how the in-group variance (i.e. the spread within all observations of a single site) compares to the out-group variance (i.e. the spread from other sites).  Results: Significant differences in emissivity spectra emerged among the four sites. PCA indicated that the first three components explain 85.5% of spectral variance, distinguishing Kingfisher as notably unique, with Sandpiper and Osprey exhibiting the greatest similarity. The KNN analysis corroborated PCA findings, reaching optimal classification accuracy (47%) at k = 21. ANOVA highlighted significant variability among the sites, especially in the spectral slope parameter (F = 762.8), suggesting differences in particle size distribution and space weathering could be driving factors in the detected heterogeneity [9]. Band ratio analyses provided additional insight into site-specific mineralogical distinctions, notably the relationship between silicate features and aqueous alteration indicators [10].  Figure 2: Distributions of Band Parameters by Site Discussion: Variability in spectral parameters aligns with documented particle size frequency distributions and known space weathering spectral types across Bennu’s surface [9]. Nightingale, the mission’s selected sample site, captures representative global characteristics, contrasting with Kingfisher’s distinct compositional and physical attributes, potentially related to differences in Fe/Mg content and degree of aqueous alteration [10].  Conclusion: Integrative use of multiple statistical approaches confirms the compositional and physical diversity of Bennu's surface, as seen through the four prospective sites. These analyses provide a framework for interpreting returned sample data and offer insights into the connections between mineralogy, particle size, and space weathering processes on small airless body surfaces.  References: [1] Lauretta D. S. et al (2021) Sample Return Missions. [2] Hamilton V. et al. (2021) A&A (Vol. 650). [3] Christensen, P. R. et al. (2019) NASA Planetary Data System [4] Christensen P. R. et al. (2018) Space Science Reviews (Vol. 214, Issue 5). [5] Rizk B. et al (2018) Space Science Reviews (Vol. 214, Issue 1). [6] Xie B. et al (2022) Minerals (Vol. 508, Issue 12). [7] Kramer O. (2013) Intelligent Systems Reference Library (13-23). [8] Sawyer S. (2009) Journal of Manual & Manipulative Therapy. [9] Clark B. E. et al (2023) Icarus (Vol. 400). [10] Bates H. et al (2020) MaPS (Vol. 55, Issue 1).