Multiwavelength Observations of Jupiter Trojans and Related Primitive Asteroid Populations

Abstract

The distribution of small Solar System bodies preserves a record of both initial conditions within the Solar nebula as well as the subsequent orbital evolution of planetary bodies. As they have undergone little geothermal evolution since their formation, primitive asteroids, including D- & P-type asteroids in the Main Belt and Jupiter Trojan clouds, represent an important reservoir of information about the history of the Solar System. The unique gravitational relationship between Jupiter and its Trojan asteroids closely ties their orbital migration histories together. Similarly, the distribution of D- & P-type asteroids within the Main Belt reveals the extent of delivery of volatile outer Solar System materials to the inner Solar System. Understanding both these processes is critical to telling the story of how our planetary system came to be.

Astronomers use spectroscopy as a tool to understand small bodies on a population level. The characteristic spectral features of asteroids reveal their compositions, and in turn, their origins. Much of asteroid spectroscopy is conducted in the visible and near-infrared (VNIR) due to its accessibility to ground-based telescopes. However, D- & P-type asteroids are red and spectrally featureless in the VNIR region, providing few constraints on the compositional makeup of these critical populations. To address this lack of constraints, I present three spectroscopic investigations of primitive asteroids in the Main Belt and Trojan clouds from the near-ultraviolet to the mid-infrared. Integrating ground-based, space-based, and airborne observations, I present analyses of the spectra of D- & P-type asteroids throughout the Solar System.

In the ultraviolet, I use the Hubble Space Telescope to observe a new spectral feature of the Jupiter Trojans, an increase in reflectance shortwards of 0.35 µm. I use Hapke optical modeling to derive compositional constraints based on this new spectral feature and demonstrate that Rayleigh scattering from submicroscopic opaques, including iron and carbon, can explain this increase in UV reflectance. In the mid-infrared, I combine observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Spitzer Space Telescope to parameterize the 10- and 20-µm silicate emission feature of Main Belt D- and P-type asteroids, comparing the appearance of this feature in Main Belt asteroids to its appearance in literature spectra of the Jupiter Trojans. I show that asteroids that otherwise appear similar in the VNIR region show a diversity of spectral features in the mid-infrared. In the VNIR, I use the Lowell Discovery Telescope and the NASA Infrared Telescope Facility to search for steeply red-sloped primitive asteroids in the Main Belt. I identify red-sloped asteroids and show that subtle differences in the VNIR spectra of Main Belt red-sloped asteroids suggest multiple sub-populations of red-sloped asteroids are present in the Main Belt.