Weak spectral features on (101995) Bennu from the OSIRIS-REx Visible and InfraRed Spectrometer

Simon-Miller, A. A.; Kaplan, H. H.; Cloutis, E. A.; Hamilton, Victoria E.; Lantz, C.; Reuter, Dennis C.; Trang, D.; Fornasier, S.; Clark, B. E.; Лауретта, Д. С.

doi:10.1051/0004-6361/202039688

Cited by 27 publications

(16 citation statements)

References 43 publications

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“…1 and 2). This anticorrelation is reported also by Li et al (2020) and Simon et al (2020b) and attributed to the presence of a ∼0.55 µm band consistent with iron oxides, which is deepest in the reddest areas (Simon et al 2020b).…”

Section: Bennu Spectral Behaviorsupporting

confidence: 84%

Phase reddening on asteroid Bennu from visible and near-infrared spectroscopy

Fornasier

Hasselmann

Deshapriya

et al. 2020

A&A

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Context. The NASA mission OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) has been observing near-Earth asteroid (101955) Bennu in close proximity since December 2018. The spacecraft has collected, on October 2020, a sample of surface material from Bennu to return to Earth. Aims. In this work, we investigate spectral phase reddening-that is, the variation of spectral slope with phase angle-on Bennu using spectra acquired by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) covering a phase angle range of 8-130 o. We investigate this process at the global scale and for some localized regions of interest (ROIs), including boulders, craters, and the designated sample collection sites of the OSIRIS-REx mission. Methods. Spectra were wavelength-and flux-calibrated, then corrected for the out-of-band contribution and thermal emission, resampled, and finally converted into radiance factor per standard OVIRS processing. Spectral slopes were computed in multiple wavelength ranges from spectra normalized at 0.55 µm. Results. Bennu has a globally negative spectra slope, which is typical of B-type asteroids. The spectral slope gently increases in a linear way up to a phase angle of 90 • , where it approaches zero. The spectral phase reddening is monotonic and wavelength-dependent with highest values in the visible range. Its coefficient is 0.00044 µm −1 deg −1 in the 0.55-2.5 µm range. For observations of Bennu acquired at high phase angle (130 •), phase reddening increases exponentially, and the spectral slope becomes positive. Similar behavior was reported in the literature for the carbonaceous chondrite Mukundpura in spectra acquired at extreme geometries. Some ROIs, including the sample collection site, Nightingale, have a steeper phase reddening coefficient than the global average, potentially indicating a surface covered by fine material with high micro-roughness. Conclusions. The gentle spectral phase reddening effect on Bennu is similar to that observed in ground-based measurements of other B-type asteroids, but much lower than that observed for other low-albedo bodies such as Ceres or comet 67P/Churyumov-Gerasimenko. Monotonic reddening may be associated with the presence of fine particles at micron scales and/or of particles with fractal structure that introduce micro-and sub-micro roughness across the surface of Bennu.

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Section: Bennu Spectral Behaviorsupporting

confidence: 84%

Phase reddening on asteroid Bennu from visible and near-infrared spectroscopy

Fornasier

Hasselmann

Deshapriya

et al. 2020

A&A

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“…This suggests that a continuum of various thicknesses of fine-particulate material on slab-like surfaces can mimic the range of spectral variations on Bennu. However, none of our mudpies-not even this areal mixture- mimic the higher frequency absorption features of Bennu's surface (Barucci et al 2020;Simon et al 2020b).…”

Section: Discussionmentioning

confidence: 77%

“…Asteroid (101955) Bennu (formerly known as 1999 RQ36), the target of the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) sample return mission (Lauretta et al 2017(Lauretta et al , 2021, is a near-Earth asteroid classified as a B-type, with carbonaceous chondrite-like albedo and spectral properties (Clark et al 2011). Bennu has a relatively flat blue reflectance spectrum and a low albedo (~4.5%), with a few minor spectral features (Hergenrother et al 2013;Takir et al 2015;DellaGiustina et al 2019;Hamilton et al 2019;Simon et al 2020aSimon et al , 2020b.…”

Section: Introductionmentioning

confidence: 99%

“…Bennu's low albedo could be explained by opaque components such as those found in carbonaceous chondrite meteorites: organics, magnetite, graphite, and/or troilite (Cloutis et al 2011a(Cloutis et al , 2011bKaplan et al 2019;Simon et al 2020a). Recent studies find good evidence for organics on Bennu (Simon et al 2020a) and some evidence for magnetite (Lauretta et al 2019;Simon et al 2020b;Hamilton et al 2021); however, recent studies also find evidence for carbonates on Bennu (Kaplan et al 2020), apparently occurring in small localized deposits and/or veins. While the presence of organics and magnetite is consistent with Bennu's low albedo, the presence of carbonates in some boulders may be elevating albedo, resulting in the observed significantly wide range of albedos found on Bennu (e.g., 3.4-7% in units of normal albedo reported in .…”

Section: Introductionmentioning

confidence: 99%

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Spectral effects of varying texture and composition in two‐component “mudpie” simulations: Insights for asteroid (101955) Bennu

Sen

Clark

Cloutis

et al. 2021

Meteorit & Planetary Scien

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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 twocomponent 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.

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“…We aim to study the possibilities of neural network-based classifiers further with the upcoming survey data from Gaia and the Large Synoptic Survey Telescope observations over photometric colors (Jones et al 2015), and with the disk-resolved spectral data from the spacecraft observations such as the JAXA Hayabusa observations of the asteroid (25143) Itokawa (Abe et al 2006) or NASA OSIRIS-REx observations of the asteroid (101955) Bennu (Simon et al 2020).…”

Section: Discussionmentioning

confidence: 99%

Asteroid spectral taxonomy using neural networks

Penttilä

Hietala

Muinonen

2021

A&A

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Aims. We explore the performance of neural networks in automatically classifying asteroids into their taxonomic spectral classes. We particularly focus on what the methodology could offer the ESA Gaia mission. Methods. We constructed an asteroid dataset that can be limited to simulating Gaia samples. The samples were fed into a custom-designed neural network that learns how to predict the samples’ spectral classes and produces the success rate of the predictions. The performance of the neural network is also evaluated using three real preliminary Gaia asteroid spectra. Results. The overall results show that the neural network can identify taxonomic classes of asteroids in a robust manner. The success in classification is evaluated for spectra from the nominal 0.45–2.45 μm wavelength range used in the Bus-DeMeo taxonomy, and from a limited range of 0.45–1.05 μm following the joint wavelength range of Gaia observations and the Bus-DeMeo taxonomic system. Conclusions. The obtained results indicate that using neural networks to execute automated classification is an appealing solution for maintaining asteroid taxonomies, especially as the size of the available datasets grows larger with missions like Gaia.

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Weak spectral features on (101995) Bennu from the OSIRIS-REx Visible and InfraRed Spectrometer

Cited by 27 publications

References 43 publications

Phase reddening on asteroid Bennu from visible and near-infrared spectroscopy

Phase reddening on asteroid Bennu from visible and near-infrared spectroscopy

Spectral effects of varying texture and composition in two‐component “mudpie” simulations: Insights for asteroid (101955) Bennu

Asteroid spectral taxonomy using neural networks

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