Editing Nebular hypothesis (section)

== Meaning of ''accretion'' ==
Use of the term "[[accretion disk]]" for the [[protoplanetary disk]] leads to confusion over the [[planetary accretion]] process.
The protoplanetary disk is sometimes referred to as an accretion disk, because while the young [[T Tauri star|T Tauri]]-like protostar is still contracting, gaseous material may still be falling onto it, accreting on its surface from the disk's inner edge.<ref name=Yorke1999 /> In an accretion disk, there is a net flux of mass from larger radii toward smaller radii.<ref name=lynden-bell_1974 />

However, that meaning should not be confused with the process of accretion forming the planets. In this context, accretion refers to the process of cooled, solidified grains of dust and ice orbiting the [[protostar]] in the protoplanetary disk, colliding and sticking together and gradually growing, up to and including the high-energy collisions between sizable [[planetesimal]]s.<ref name=Kokubo2002 />

In addition, the [[giant planet]]s probably had accretion disks of their own, in the first meaning of the word.<ref name=dangelo_podolak_2015>{{cite journal |last=D'Angelo |first=G. |author2= Podolak, M. |title= Capture and Evolution of Planetesimals in Circumjovian Disks |journal= The Astrophysical Journal |date= 2015 |volume=806 |issue=1 |pages=29pp |doi= 10.1088/0004-637X/806/2/203|arxiv = 1504.04364 |bibcode = 2015ApJ...806..203D|s2cid=119216797 }}</ref> The clouds of captured hydrogen and helium gas contracted, spun up, flattened, and deposited gas onto the surface of each giant [[protoplanet]], while solid bodies within that disk accreted into the giant planet's regular moons.<ref name=Canup2002>{{cite journal |last=Canup |first=Robin M. |author1-link=Robin Canup |author2= Ward, William R. |title= Formation of the Galilean Satellites: Conditions of Accretion |journal= The Astronomical Journal |date=2002 |volume=124 |issue=6 |pages=3404–3423 |doi= 10.1086/344684 |url= http://www.boulder.swri.edu/~robin/cw02final.pdf |bibcode= 2002AJ....124.3404C|s2cid=47631608 }}</ref>