Revealing Refractory Materials on Trans-Neptunian Objects and Centaurs via Reflectance Spectroscopy

Abstract

This thesis presents visual and near-infrared spectroscopic observations of Trans-Neptunian Objects and centaurs obtained over four observing runs at the ESOVery Large Telescope. The reflectance spectra of these minor planets were investigated to determine whether silicates and refractory organics, which are predicted to be present on their surfaces, could be directly detected via the presence of their characteristic absorption bands. Most of the objects observed exhibit reflectance spectra typical of TNOs, without characteristic absorption bands attributable to silicates or refractory hydrocarbons. The reflectance spectra of two objects, however, were confirmed to exhibit atypical behaviour at visual wavelengths. A near-UV absorption edge confirmed in the reflectance spectrum of 2012 DR30 at l < 0.6 mm was concluded to be most consistent with similar absorption edges present in the reflectance spectra of aromatic refractory hydrocarbons. It was hypothesised that highly aromatised hydrocarbons may be present on this object due to the long periods it spends in regions of strong interstellar radiation. The spectrum of 2004 EW95, a TNO on an orbit resonant with that of Neptune, was confirmed through photometry and multiple spectroscopic observations to possess absorption bands at visual wavelengths that were attributable to ferric oxides and aqueously altered silicates.These gave the spectrum a similar appearance to those possessed by hydrated C-type asteroids. The spectrum of 2004 EW95, in combination with its dynamical characteristics, suggests that this object formed in the giant planet region and was subsequently scattered into the Trans-Neptunian Belt as a result of the early migrations of the giant planets. 174P/Echeclus, an active centaur,was observed consistently before and after its cometary outburst in 2016 to determine if any resulting surface changes would be detectable. The reflectance spectrum of 174P/Echeclus was not observed to change, but the visual colour of the residual dust coma was observed to be surprisingly blue, suggesting that it may have a carbon-rich composition. Deposition of enough of this blue dust onto the surface of a red active centaur through successive episodes of activity may be a mechanism by which its colour could become neutralised.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Alan Fitzsimmons (Supervisor) & Christopher Watson (Supervisor)