arXiv subjects

David C. Cantillo

Publications and source records attributed to David C. Cantillo.

5 recordsLinked to original sources

arXiv2026

Size Constraints for the Pre-atmospheric Parent Bodies of Ordinary Chondrites

The study of S-complex near-Earth objects (NEOs), the parent bodies of ordinary chondrites, has shown that they are dominated by asteroids with LL chondrite-like compositions. This is surprising because among the three subtypes of ordinary chondrites (H, L, and LL), LL chondrites are the least common, representing only 10\% of all ordinary chondrite falls. This discrepancy has been attributed to the size of the NEOs studied, which are likely too large to be the immediate precursors of the meteorites that fall on Earth. To test this hypothesis, we obtained near-infrared spectra (0.7-2.5 $μ$m) of a group of objects with absolute magnitudes 20.0 $\leq$ $H$ $\leq$ 29.2 (sizes $\sim$4-343 m). The sample was divided into subgroups based on their $H$ value, and the composition of the asteroids was determined. We found that the dominance of LL chondrite-like objects disappears at sizes of $\sim$31-49 m. At this size range, asteroids with L chondrite-like compositions become dominant, matching the fraction of L chondrite meteorite falls. In contrast, the fraction of H chondrite-like NEOs was found to be much lower than the proportion of H chondrite falls, even among the smallest objects. We determined an upper size limit of $\sim$18 m for the parent bodies of these meteorites. The same upper limit was established for the pre-atmospheric parent bodies of LL chondrites. These results constitute the first observational evidence for a size dependence in the composition of S-complex NEOs.

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arXiv2024

The population of small near-Earth objects: composition, source regions and rotational properties

The study of small ($<$300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs, which include near-infrared (NIR) spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising $\sim$66\% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex, but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock-darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83\% of the NEOs escaped from the $ν_{6}$ resonance, 16\% from the 3:1 and just 1\% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.

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arXiv2024

Grain Size Effects on UV-MIR (0.2-14 micron) Spectra of Carbonaceous Chondrite Groups

Carbonaceous chondrites are among the most important meteorite types and have played a vital role in deciphering the origin and evolution of our solar system. They have been linked to low-albedo C-type asteroids, but due to subdued absorption bands, definitive asteroid-meteorite linkages remain elusive. A majority of these existing linkages rely on fine-grained (typically < 45 micron) powders across a limited wavelength range in the visible to near-infrared (0.35-2.5 microns). While this is useful in interpreting the fine-grained regolith of larger main-belt objects like Ceres, recent spacecraft missions to smaller near-Earth asteroids (NEAs), such as Bennu and Ryugu, have shown that their surfaces are dominated by larger grain size material. To better interpret the surfaces of these smaller, carbonaceous NEAs, we obtained laboratory reflectance spectra of seven carbonaceous chondrite meteorite groups (CI, CM, CO, CV, CR, CK, C2-ungrouped) over the ultraviolet to mid-infrared range (0.2-14 microns). Each meteorite contained five grain size bins (45-1000 microns) to help constrain spectral grain size effects. We find a correlation between grain size and absolute reflectance, spectral slope, band depth, and the Christiansen feature band center. Principal component analysis of grain size variation illustrates a similar trend to lunar-style space weathering. We also show that the Bus-DeMeo asteroid taxonomic classification of our samples is affected by grain size, specifically shifting CM2 Aguas Zarcas from a Ch-type to B-type with increasing grain size. This has implications for the parent body of the OSIRIS-REx target, Bennu. With Aguas Zarcas, we present results from Hapke modeling.

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arXiv2021

Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986 DA) and 2016 ED85

Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA population that is mostly dominated by S- and C-type asteroids. Because of this, their identification and study provide us with a unique opportunity to learn more about the formation and evolution of this particular type of bodies, as well as their relationship with meteorites found on Earth. We present near-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We found that the spectral characteristics of these objects are consistent with those of metal-rich asteroids, showing red slopes, convex shapes, and a weak pyroxene absorption band at $\sim$0.93 $μ$m. The compositional analysis showed that they have a pyroxene chemistry of Fs$_{40.6\pm3.3}$Wo$_{8.9\pm1.1}$ and a mineral abundance of $\sim$15% pyroxene and 85% metal. We determined that these objects were likely transported to the near-Earth space via the 5:2 mean motion resonance with Jupiter. Asteroid spectra were compared with the spectra of mesosiderites and bencubbinites. Differences in the NIR spectra and pyroxene chemistry suggest that bencubbinites are not good meteorite analogs. Mesosiderites were found to have a similar pyroxene chemistry and produced a good spectral match when metal was added to the silicate component. We estimated that the amounts of Fe, Ni, Co, and the platinum group metals present in 1986 DA could exceed the reserves worldwide.

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arXiv2021

Constraining the Regolith Composition of Asteroid (16) Psyche via Laboratory Near-infrared Spectroscopy

(16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Discovery-class Psyche mission. Despite gaining considerable interest in the scientific community, Psyche's composition and formation remain unconstrained. Originally, Psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. More recent telescopic observations suggest the additional presence of low-Fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. To better understand the abundances of these additional materials, we investigated visible near-infrared (0.35 - 2.5 micron) spectral properties of three-component laboratory mixtures of metal, low-Fe pyroxene, and carbonaceous chondrite. We compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) Psyche to constrain material abundances. We find that the best matching mixture to Psyche consists of 82.5% metal, 7% low-Fe pyroxene, and 10.5% carbonaceous by weight, suggesting that the asteroid is less metallic than originally estimated (~94%). The relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to Psyche's surface. Assuming that Psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates.

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