Clearing of protoplanetary disks

The clearing of protoplanetary disks and of the proto-solar nebula... 

In order to understand fully the evolution of protoplanetary disks, it is necessary to develop an understanding of the dynamics and evolution of both the gas and solids that they contain. The detailed evolution of these components are often discussed separately, largely owing to our incomplete understanding of the processes involved. In introducing the different concepts in this chapter, we too will treat these components separately in order to present a clear picture of the fundamental processes that are believed to be at work. We will discuss the feedback that takes... 

In this chapter we compare the evolution of protoplanetary disks to that of the proto-solar nebula. We start by summarizing the observational constraints on the lifetime of protoplanetary disks and discuss four major disk-dispersal mechanisms. Then, we seek constraints on the clearing of gas and dust in the proto-solar nebula from the properties of meteorites, asteroids, and planets. Finally, we try to anchor the evolution of protoplanetary disks to the Solar System chronology and discuss what observations and experiments are needed to understand how common is the history of the Solar System. 

The lines of evidence from CAIs and AOAs suggest that disk gas was present in the earliest epoch of solid formation in the Solar System. However, it is not clear what stage of the proto-solar disk evolution corresponds to the earliest solid formation in the Solar System. This makes it difficult to compare the evolution of the proto-solar disk with that of protoplanetary disks (see Section 9.4). 

Hester, J. J. and Desch, S. J. (2005) Understanding our origins Star formation in HII region environments. In Chondrites and the Protoplanetary Disk, ASP Conference Series, 341, eds. Krot, A. N., Scott, E. R. D. and Reipurth, A. San Francisco Astronomical Society of the Pacific, pp. 107-130. A clear and up-to-date review of astronomical observations that constrain models for solar system formation. 

This book is the first comprehensive overview of planet formation, in which astronomers, cosmochemists, and laboratory astrophysicists jointly discuss the latest insights from the Spitzer and Hubble space telescopes, new interferometers, space missions including Stardust and Deep Impact, and laboratory techniques. Following the evolution of solids from their genesis through protoplanetary disks to rocky planets, the book discusses in detail how the latest results from these disciplines fit into a coherent picture. This volume provides a clear introduction and valuable reference for students and researchers in astronomy, cosmochemistry, laboratory astrophysics, and planetary sciences. 

A protoplanetary disk contains gas and dust. The chemistry is dominated by freeze out and low temperature ion-molecule reactions. Outflows and UV radiation clear out most of the envelope, leaving a protoplanetary disk with the inner gap between the disk and the star. Close to the dust inner rim temperatures are high and X-rays heat dust and gas, which in turn excite molecular lines such as Ha, fine-structure lines, and HaO, among others. The middle planes are cold and gas is frozen out on dust grains. The outer disk is irradiated by UV light from the star showing mostly molecular rotational lines in the form of ions and radicals. 

Herschel Open Time Key Program Gas in Protoplanetary Systems 1 will obtain spectra of far-infrared atomic and molecular lines from over 240 disks in nearby star-forming regions with ages in the critical 1-30 Myr range over which gas clears out and planets form. 

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