Infrared Spectroscopy of Large, Low‐Albedo Asteroids: Are Ceres and Themis Archetypes or Outliers?
AffiliationUniv Arizona, Lunar & Planetary Lab
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationRivkin, A. S., Howell, E. S., & Emery, J. P. ( 2019). Infrared spectroscopy of large, low‐albedo asteroids: Are Ceres and Themis archetypes or outliers? Journal of Geophysical Research: Planets, 124, 1393– 1409.
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AbstractLow-albedo, hydrated objects dominate the list of the largest asteroids. These objects have varied spectral shapes in the 3-m region, where diagnostic absorptions due to volatile species are found. Dawn's visit to Ceres has extended the view shaped by ground-based observing and shown that world to be a complex one, potentially still experiencing geological activity. We present 33 observations from 2.2 to 4.0m of eight large (D>200km) asteroids from the C spectral complex, with spectra inconsistent with the hydrated minerals we see in meteorites. We characterize their absorption band characteristics via polynomial and Gaussian fits to test their spectral similarity to Ceres, the asteroid 24 Themis (thought to be covered in ice frost), and the asteroid 51 Nemausa (spectrally similar to the CM meteorites). We confirm most of the observations are inconsistent with what is seen in meteorites and require additional absorbers. We find clusters in band centers that correspond to Ceres- and Themis-like spectra, but no hiatus in the distribution suitable for use to simply distinguish between them. We also find a range of band centers in the spectra that approaches what is seen on Comet 67P. Finally, variation is seen between observations for some objects, with the variation on 324 Bamberga consistent with hemispheric-level difference in composition. Given the ubiquity of objects with 3-m spectra unlike what we see in meteorites, and the similarity of those spectra to the published spectra of Ceres and Themis, these objects appear much more to be archetypes than outliers.
Note6 month embargo; first published: 17 April 2019
VersionFinal published version
SponsorsNASA Planetary Astronomy program; SOFIA [SOF 04-0050]; SSO [NNX16AE91G]; L. A. Taylor Endowment; National Aeronautics and Space Administration [NNH14CK55B]; [NNX14AJ39G]; [NNX09AB45G]; [NNG05GR60G]; [NAG5-10604]