Near-UV behaviour of observed TNO reflectance spectra

Tom Seccull, Wesley Cristopher Fraser, Matthew Izawa, Michael E. Brown

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Observed spectra provide the best diagnostics of the surface compositions of Trans-Neptunian Objects (TNOs). We have observed the spectra of 7 TNOs, from across almost the full range of dynamical classes, using the VLT's X-Shooter spectrograph. Compared to the 5 targets in our sample which exhibit linear spectra in the UV-optical range, two of of our targets show highly unusual spectral behaviour, whereby their reflectance decreases sharply at wavelengths below ~440nm. Those same objects exhibit typically unremarkable spectra in the optical and near-IR spectral regions. In these regions where available, our observed spectra of the targets are in agreement with spectra or photometry available in the literature. Using a different solar analogue to produce our reflectance spectra does not remove the UV decrease exhibited by the two targets. Further, it appears that neither reducing the spectra with different pipelines, nor using drastically different parameters in those pipelines changes this general behaviour. Based on laboratory spectra of complex hydrocarbons it is plausible that the near-UV behaviour is the result of a surface coating of organic substances on the TNOs which exhibit it. The spectra of organics are also consistent in having a general red slope similar to that observed in the spectra of many TNOs. While laboratory spectra of some silicate substances also show a decrease in reflectance in the near-UV spectral region that is in principle consistent with our observations, those silicates do not exhibit a red slope consistent with our optical spectra. Hence, the hypothesis that silicates are present seems less likely than the hypothesis that this UV decrease is due to the presence of organics on the surfaces of these objects.
Original languageEnglish
Title of host publication227th Meeting of the American Astronomical Society: Proceedings
Publication statusPublished - 01 Oct 2016
Externally publishedYes
Event227th Meeting of the American Astronomical Society (AAS) - Gaylord Palms Resort & Convention Center in Kissimmee, Florida, United States
Duration: 04 Jan 201608 Jan 2016


Conference227th Meeting of the American Astronomical Society (AAS)
CountryUnited States
Internet address

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    Seccull, T., Fraser, W. C., Izawa, M., & Brown, M. E. (2016). Near-UV behaviour of observed TNO reflectance spectra. In 227th Meeting of the American Astronomical Society: Proceedings (Vol. 48)