Dust Properties and Assembly of Large Particles in Protoplanetary Disks

o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o oo o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Recent research n the buildup f r cks fr m small dust grains has reaffirmed that grain gr wth in pr t planetary disks sh uld ccur quickly. Calculati n f gr wth rates have been made f r a variety f gr wth pr cesses and generally predict high pr babilities f sticking in l w-vel city c llisi ns, which may be br ught ab ut in a number f ways in pr t planetary disks. Lab rat ry experiments have measured sticking c efficients f r s me materials, largely c nfirming the calculati ns. Alth ugh the detailed vel city fields f disks are n t well underst d, many f the imp rtant pr cesses leading t particle c llisi ns and grain gr wth have been studied the retically and dem nstrate likely paths by which dust is assembled int planets. Calculati ns f the radiative pr perties f particles with vari us size distributi ns sh w that large particles sh uld pr duce bservable changes in the spectral energy distributi ns f disks. Changes f the s rt predicted are, in fact, bserved, but their interpretati n is ambigu us; there are ther ways t pr duce the bserved changes that d n t require grain gr wth, s the evidence is currently inc nclusive. The maj r uncertainties can be verc me with the next generati n f millimeter-wave interfer meters, and it seems likely that a firm case f r grain gr wth c uld be established within a decade.