Geology: A → sedimentary particle that is between 4 and 64 mm in size. Pebbles are larger than → granules but smaller than → cobbles. Pebbles have typically been rounded by → abrasion during sedimentary transport (geology.com/dictionary).
From M.E. pibel, from O.E. *papol, *pyppel, *pæbbel, of unknown origin.
Rig, from Mid.Pers. rik "pebble, sand."
Fr.: accrétion de galets
A planet formation concept that concerns the → accretion of small objects of negligible gravitational mass (ranging from centimeters up to meters in diameter) onto large, gravitating bodies: → planetesimals, → protoplanets, or → planets. In a more narrow sense, pebble accretion is an accretion process where (gas) drag and gravity play major roles. Simply put, this means that the pebble has to be aerodynamically small and the planet to be gravitationally large (C. W. Ormel, in Formation, Evolution, and Dynamics of Young Solar Systems, p. 197, eds. M. Pessah, O. Gressel, Springer, 2017).