Spectrophotometric modeling and mapping of Ceres

Jian Yang Li, Stefan E. Schröder, Stefano Mottola, Andreas Nathues, Julie C. Castillo-Rogez, Norbert Schorghofer, David Williams, Mauro Ciarniello, Andrea Longobardo, Carol A. Raymond, Christopher T. Russell

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

We report a comprehensive analysis of the global spectrophotometric properties of Ceres using the images collected by the Dawn Framing Camera through seven color filters from April to June 2015 during the RC3 (rotational characterization 3) and Survey mission phases. We derived the Hapke model parameters for all color filters. The single-scattering albedo of Ceres at 555 nm wavelength is 0.14 ± 0.04, the geometric albedo is 0.096 ± 0.006, and the bolometric Bond albedo is 0.037 ± 0.002. The asymmetry factors calculated from the best-fit two-term Henyey-Greenstein (HG) single-particle phase functions (SPPFs) show a weak wavelength dependence from −0.04 at 438 nm increasing to 0.002 at >900 nm, suggesting that the phase reddening of Ceres is dominated by single-particle scattering rather than multiple scattering or small-scale surface roughness. The Hapke roughness parameter of Ceres is derived to be 20° ± 6° with no wavelength dependence. The phase function of Ceres presents appreciably strong scattering around 90° phase angle that cannot be fitted with a single-term HG SPPF, suggesting possible stronger forward scattering component than other asteroids previously analyzed with spacecraft data. We speculate that such a scattering characteristic of Ceres might be related to its ubiquitous distribution of phyllosilicates and high abundance of carbonates on the surface. We further grouped the reflectance data into a 1° latitude-longitude grid over the surface of Ceres, and fitted each grid independently with both empirical models and the Hapke model to study the spatial variations of photometric properties. Our derived albedo maps and color maps are consistent with previous studies [Nathues, A., et al., 2016, Planet. Space Sci. 134, 122–127; Schröder, S.E., et al., 2017, Icarus 288, 201–225]. The SPPF over the surface of Ceres shows an overall correlation with albedo distribution, where lower albedo is mostly associated with stronger backscattering and vice versa, consistent with the general trend among asteroids. On the other hand, the Hapke roughness parameter does not vary much across the surface of Ceres, except for the ancient Vendimia Planitia region that is associated with a slightly higher roughness. Furthermore, the spatial distributions of the SPPF and the Hapke roughness do not depend on wavelength. Based on the wavelength dependence of the SPPF of Ceres, we hypothesize that the regolith grains on Ceres either contain a considerable fraction of μm-sized or smaller particles, or are strongly affected by internal scatterers of this size.

Original languageEnglish (US)
Pages (from-to)144-167
Number of pages24
JournalIcarus
Volume322
DOIs
StatePublished - Apr 1 2019

Fingerprint

albedo
scattering
roughness
wavelength
modeling
wavelengths
asteroids
color
asteroid
grids
filter
framing cameras
filters
regolith
phyllosilicate
forward scattering
longitude
particle
surface roughness
planets

Keywords

  • Asteroid Ceres
  • Asteroids, surfaces
  • Photometry
  • Spectrophotometry

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Li, J. Y., Schröder, S. E., Mottola, S., Nathues, A., Castillo-Rogez, J. C., Schorghofer, N., ... Russell, C. T. (2019). Spectrophotometric modeling and mapping of Ceres. Icarus, 322, 144-167. https://doi.org/10.1016/j.icarus.2018.12.038

Spectrophotometric modeling and mapping of Ceres. / Li, Jian Yang; Schröder, Stefan E.; Mottola, Stefano; Nathues, Andreas; Castillo-Rogez, Julie C.; Schorghofer, Norbert; Williams, David; Ciarniello, Mauro; Longobardo, Andrea; Raymond, Carol A.; Russell, Christopher T.

In: Icarus, Vol. 322, 01.04.2019, p. 144-167.

Research output: Contribution to journalArticle

Li, JY, Schröder, SE, Mottola, S, Nathues, A, Castillo-Rogez, JC, Schorghofer, N, Williams, D, Ciarniello, M, Longobardo, A, Raymond, CA & Russell, CT 2019, 'Spectrophotometric modeling and mapping of Ceres', Icarus, vol. 322, pp. 144-167. https://doi.org/10.1016/j.icarus.2018.12.038
Li JY, Schröder SE, Mottola S, Nathues A, Castillo-Rogez JC, Schorghofer N et al. Spectrophotometric modeling and mapping of Ceres. Icarus. 2019 Apr 1;322:144-167. https://doi.org/10.1016/j.icarus.2018.12.038
Li, Jian Yang ; Schröder, Stefan E. ; Mottola, Stefano ; Nathues, Andreas ; Castillo-Rogez, Julie C. ; Schorghofer, Norbert ; Williams, David ; Ciarniello, Mauro ; Longobardo, Andrea ; Raymond, Carol A. ; Russell, Christopher T. / Spectrophotometric modeling and mapping of Ceres. In: Icarus. 2019 ; Vol. 322. pp. 144-167.
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AU - Mottola, Stefano

AU - Nathues, Andreas

AU - Castillo-Rogez, Julie C.

AU - Schorghofer, Norbert

AU - Williams, David

AU - Ciarniello, Mauro

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N2 - We report a comprehensive analysis of the global spectrophotometric properties of Ceres using the images collected by the Dawn Framing Camera through seven color filters from April to June 2015 during the RC3 (rotational characterization 3) and Survey mission phases. We derived the Hapke model parameters for all color filters. The single-scattering albedo of Ceres at 555 nm wavelength is 0.14 ± 0.04, the geometric albedo is 0.096 ± 0.006, and the bolometric Bond albedo is 0.037 ± 0.002. The asymmetry factors calculated from the best-fit two-term Henyey-Greenstein (HG) single-particle phase functions (SPPFs) show a weak wavelength dependence from −0.04 at 438 nm increasing to 0.002 at >900 nm, suggesting that the phase reddening of Ceres is dominated by single-particle scattering rather than multiple scattering or small-scale surface roughness. The Hapke roughness parameter of Ceres is derived to be 20° ± 6° with no wavelength dependence. The phase function of Ceres presents appreciably strong scattering around 90° phase angle that cannot be fitted with a single-term HG SPPF, suggesting possible stronger forward scattering component than other asteroids previously analyzed with spacecraft data. We speculate that such a scattering characteristic of Ceres might be related to its ubiquitous distribution of phyllosilicates and high abundance of carbonates on the surface. We further grouped the reflectance data into a 1° latitude-longitude grid over the surface of Ceres, and fitted each grid independently with both empirical models and the Hapke model to study the spatial variations of photometric properties. Our derived albedo maps and color maps are consistent with previous studies [Nathues, A., et al., 2016, Planet. Space Sci. 134, 122–127; Schröder, S.E., et al., 2017, Icarus 288, 201–225]. The SPPF over the surface of Ceres shows an overall correlation with albedo distribution, where lower albedo is mostly associated with stronger backscattering and vice versa, consistent with the general trend among asteroids. On the other hand, the Hapke roughness parameter does not vary much across the surface of Ceres, except for the ancient Vendimia Planitia region that is associated with a slightly higher roughness. Furthermore, the spatial distributions of the SPPF and the Hapke roughness do not depend on wavelength. Based on the wavelength dependence of the SPPF of Ceres, we hypothesize that the regolith grains on Ceres either contain a considerable fraction of μm-sized or smaller particles, or are strongly affected by internal scatterers of this size.

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