Gas in Protoplanetary and Debris Disks: Insights from UV Spectroscopy

Over the last two decades, observations of protoplanetary and debris disks have played an important role in the new field of extrasolar planetary studies. Many are familiar with the extensive work on cold circumstellar dust present in these disks, primarily performed using infrared and sub-millimeter photometry and spectroscopy. However, UV spectroscopy has made some unique contributions by probing the elusive but vital gas component in protoplanetary and debris disks. This article outlines our picture of the evolution of protoplanetary disks and discusses the importance of the gas component. New insights obtained from UV spectroscopy are highlighted, as well as some new puzzles. A major upcoming study of gas in disks at far-IR wavelengths is briefly described. Finally, the potential for future UV observations with proposed space telescopes aimed at characterization of habitable exoplanets is discussed.