Gas and Dust in Debris Disks: What is Normal?

The basic character of debris disks was established soon after their discovery are composed mostly of dust produced by collisions and/or evaporation of solid planetary bodies. However, several fundamental observational questions about debris disks remain unanswered. How much material do they typically contain and how does it evolve with time? How much gas to they contain? What is the composition of their dust and gas? Answers to these questions will provide insights into the late-stages of planetary system formation. In this paper, we discuss some recent progress toward addressing these questions. Observations with the Spitzer Space Telescope have shown that the amount of dust in debris disks decreases with time on averages, but also indicate that dust production is stochastic. At least some debris disks contain small amounts of gas which has very different characteristics from gas in younger protoplanetary disks. The most complete inventory of gas in a debris disk to date unexpectedly showed that the gas is extremely carbon-rich. Finally, recent studies of the albedo of dust in debris disks have shown an extraordinary range of colors, including very red colors indicative of organic material.