¹K. D. Burgess,¹R. M. Stroud
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13692]
¹U.S. Naval Research Laboratory, Washington, District of Columbia, 20375 USA
Published by arrangement with John Wiley & Sons

The return of samples from S-type asteroid 25143 Itokawa have enabled significant improvements in our understanding of space weathering on asteroids and the link between S-type asteroids and ordinary chondrites. We report on three new particles, providing details on space weathering of adjacent grains within a particle and several different phases. The features we observe are consistent with formation via irradiation from the solar wind, as opposed to micrometeoroid bombardment. We also see differences in the degree of weathering for grains collected from the two different touchdown locations on the asteroid. Continued analysis of new grains from Itokawa allow us to draw a more complete picture of the variety of space weathering features and the processes that lead to their formation on Itokawa and other airless bodies.

^1,2Giovanni Pratesi,¹Vanni Moggi Cecchi,³Richard C. Greenwood,³Ian A. Franchi,³Samantha J. Hammond,⁴Mario Di Martino,^4,5Dario Barghini,⁵Carla Taricco,⁶Albino Carbognani,⁴Daniele Gardiol
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13695]
¹Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, Florence, 50121 Italy
²INAF—Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, Rome, 00133 Italy
³Planetary and Space Sciences, The Open University, Milton Keynes, MK7 6AA UK
⁴INAF—Osservatorio Astrofisico di Torino, Via Osservatorio 20, Turin, 10025 Italy
⁵Dipartimento di Fisica, Università degli Studi di Torino, Via P. Giuria 1, Pino Torinese, 10125 Italy
⁶INAF—Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, Bologna, 40129 Italy
Published by arrangement with John Wiley & Sons

The Cavezzo meteorite, which fell on January 1, 2020, is the first meteorite detected and recovered by the Italian PRISMA Fireball Network. Two specimens, weighing 3.12 g (specimen 1) and 52.19 g (specimen 2), were collected 3 days after the bolide was observed, thanks to an effective media campaign that encouraged the involvement of local people. The two specimens of this meteorite have not only completely different lithological characteristics but also a different geochemistry and oxygen isotopic composition as well. Specimen 1 is anomalous both for the textural–structural features, varying seamlessly from chondritic to “achondritic,” and a very unusual modal mineralogy—such as the relatively high amount of olivine (63.1 vol%), plagioclase (18.2 vol%), high-Ca pyroxene (10.3 vol%), and chlorapatite (2.1 vol%); and the unusually low content of low-Ca pyroxene (5.8 vol%), metal (0.1 vol%), and troilite (much lesser than 0.1 vol%)—although the compositional values for olivine (Fa 24.24 mol%) and low-Ca pyroxene (Fs 20.41 mol%) appear to be similar to those of the L chondrite group. Conversely, in specimen 2, not only the texture and the crystal chemistry but also the modal mineralogy (low-Ca pyroxene much more abundant than high-Ca pyroxene and occurrence of metal and sulfides) look like those of an ordinary L chondrite. The differences between the two specimens are also confirmed by geochemistry. The oxygen isotope composition of specimen 1 plots at the boundary between the H and L groups (δ17O‰ 3.250; δ18O‰ 4.736; Δ17O‰ 0.788) whereas specimen 2 plots at the boundary of the L and LL fields (δ17O‰ 3.737; δ18O‰ 4.957; Δ17O‰ 1.159). The bulk chemistry shows a different content of many minor and trace elements (including rare earth elements), such as a strong depletion of siderophile and chalcophile elements in specimen 1. The two specimens then do not contain fragments of each other, thus preventing us from classifying this “double face” meteorite as an ordinary chondrite breccia. In detail, specimen 1 can be considered a “xenolith” in which chondritic structure and igneous texture coexist without discontinuity, and therefore, it represents a previously unsampled portion of the L parent body. In summary, these findings support the classification of Cavezzo as an L5 anomalous chondrite.

¹Antara Sen et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13699]
¹Department of Physics and Astronomy, Ithaca College, Ithaca, New York, 14850 USA
Published by arrangement with John Wiley & Sons

Data returned by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft have shown that asteroid (101955) Bennu has a globally low-albedo surface covered in boulders with diverse texture, color, and albedo properties, and an aqueously altered composition dominated by phyllosilicates. To test whether Bennu’s color and albedo diversity could be caused by texture and/or composition variations, we performed a laboratory-based study using simple two-component mixtures (called “mudpies”) of the phyllosilicate saponite and carbon-rich opaques. Each mudpie is prepared in four different textures: fine powder, coarse particles, sanded slab, and textured rock. We find that a sanded slab made from 90% saponite and 10% lampblack is a good analog for Bennu, and the color and albedo changes due to texture variations are substantial. At 550 nm, texture changes alone can create up to 36% brightness contrast, and in color measured as a 473 nm/847 nm ratio, texture changes can provide up to 18% color contrast. In comparison, Bennu shows approximately 25% albedo and <1% color contrasts from boulder type to boulder type. These findings suggest that if texture contributes to color on Bennu, the texture variations are typically more subtle than what we simulated in the laboratory. According to our study, the color and albedo properties of different boulder types on Bennu are consistent with different concentrations of carbon-rich opaques (and possibly consistent with variations in carbonate concentration). The variations within each boulder group are consistent with textural differences.