Watching Young Solar Systems Grow
Friday, July 17, 2009
Science Update - A look at CfA discoveries from recent journals

In fewer than ten million years the material in the circumstellar disk around a young star will either be accreted on to its star, dispersed
into the interstellar medium, or converted into planets or smaller solid bodies. It is a time of high drama. While the star's gravity tends to pull all of the disk material onto the star, small orbiting clumps of coagulated dust grains in the disk grow into larger bodies that disrupt that infall process.
The solid bodies often sculpt gaps, or cavities, in the disk, and accrete more material as some grow into planets. Eventually winds from the star will sweep away the remaining disk
material. Each of these processes is influenced by many factors that astronomers
are working hard to understand, but their efforts have so far been hampered by a lack of precise spatial information about the distribution
of the material in the disk.

SAO's Submillimeter Array (SMA) in Hawaii has enabled a new level of precision in the study of circumstellar disks, and with it a deeper understanding of how planets form. SAO astronomers Sean Andrews, David Wilner, Meredith Hughes, and Chunhua Qi, together with a colleague, used the SMA to probe the protoplanetary disks around nine bright, relatively massive disks down to sizes of about 40 AU (one AU - astronomical unit - is the average distance of the earth from the sun). They use newly improved models to measure the distribution of mass in the disk, including rings suggestive of gaps carved by planets, and to estimate other key parameters like turbulence in the material. The scientists conclude that not only does giant planet formation seem possible in all of these nine disks, it may already have begun around three of them. The absence of giant planets in the remaining six highlights the importance of other parameters, age for example. The new paper is an important landmark in combining high precision submillimeter imaging with sophisticated modeling to probe the early stages in the development of new planetary systems.