Spatially limited ion-acoustic and dusty-acoustic solitons in a magnetised dusty plasmas are investigated. The form and characteristic velocities of the solitons are studied, as well as the conditions for the existence of rarefactive and compressional solitons. The special case of a plasma consisting of ions and dust grains is also considered. The work is then applied to the creation of condensates in cometary tails and to Saturn's rings, where it provides an alternative explanation for spoke formation.