A Comparative Study of the Themis and Veritas Asteroid Families

Document Type

Conference Proceeding

Publication Date


Publication Title

Infrared Science Archive


Our primary goal is to characterize the surface composition (and other properties such as radius, albedo and thermal inertia) of our sample of Themis-family and Veritas-family asteroids based on their 5 to 14 micron spectra. We chose these two families for several reasons. First, they are compositionally primitive (non-igneous) so they can yield information about their physical and chemical conditions of their formation environment. Second, their parent bodies formed in the same region, yet their disruption ages are sharply different: 2.5 Gy and 8.3 My, respectively. This gives us a remarkable opportunity to understand the evolutionary processes that have affected the asteroids fragments. For example, Nesvorny et al. (2005) found clear evidence of color variations between young and old asteroids families. They identified a well defined trend among primitive asteroids, with the Themis and Veritas families at opposite ends of this color variation, which they attribute to space weathering. Finally, both families formed beyond the 'frost line' and some fragments appear to have retained water-ice reservoirs for the age of the solar system; more specifically Rivkin (2007) reported the first (preliminary) detection of water ice on 24 Themis. If confirmed, this detection of water-ice opens up interesting possibilities that could transform of our understanding of these asteroids. For example, since water ice is not stable on the surface of 24 Themis over the age of the solar system what is its source? What does this imply about the interior of this asteroid and of the other members of these two families. Why does 24 Themis not show cometary activity? These are some of the questions this proposed study will address. Understanding the abundance of water-ice and hydrated minerals in this area of the solar system is particularly important, as it may be linked to the origin of Earth's water. Our total time request is 6.4 hours.