VOLATILES IN PROTOPLANETARY DISKS
K. Pontoppidan (Space Telescope Science Institute, Baltimore, United States),
C. Salyk (National Optical Astronomy Observatory, United States),
E. Bergin (University of Michigan, Dept. of Astronomy, United States),
S. Brittain (Clemson University, Dept. of Physics and Astronomy, United States),
B. Marty (CRPG-CNRS, France),
O. Mousis (University of Franche-Comte, Institut UTINAM, Besancon, France),
K. Oberg (University of Virginia, United States)
Volatiles are compounds with low sublimation temperatures, and they make up most of the condensible
mass in typical planet-forming environments. They typically consist of relatively small, often hydrogenated,
molecules based on the abundant elements carbon, nitrogen and oxygen. Volatiles are
central to the process of planet formation, forming the backbone of a rich chemistry that sets the initial
conditions for the formation of planetary atmospheres, and acts as a solid mass reservoir catalyzing
the formation of planet and planetesimals. Since Protostars and Planets V, our understanding of the
evolution of volatiles in protoplanetary environments has grown tremendously. This growth has been
driven by rapid advances in observations and models of protoplanetary disks, and of a deepening understanding
of the cosmochemistry of the solar system. Indeed, it is only in the past few years that
representative samples of molecules have been discovered in great abundance throughout protoplanetary
disks (CO, H2O, HCN, C2H2, CO2, H2D+, HCO+) - enough to begin building a complete budget
for the most abundant elements after hydrogen and helium. The spatial distributions of key volatiles
are being mapped, snow lines are directly seen and quantified, and distinct chemical regions within
protoplanetary disks are being identified, characterized and modeled. Theoretical processes invoked
to explain the solar system record are now being observationally constrained in protoplanetary disks,
including transport of icy bodies and concentration of bulk condensibles, strong thermal and chemical
processing of inner disk material, along with the chemically gentle accretion of pristine material from
the interstellar medium in the outer disk. This chapter focuses on making the first steps toward knowing
whether the planet formation processes driving the final chemical makeup of our solar system are
universal.
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