Small bodies and dust in the outer solar system

We present our current understandings of small bodies and dust grains located in the outer Solar System. Small icy bodies Edgeworth-Kuiper Belt objects (EKBOs) and Oort Cloud objects orbit the Sun at distances from Neptune's orbit outward to 10(4)-10(5) AU. Both EKBOs and Oort Cloud objects are believed to be remnants of planetesimals formed in the proto-planetary disk. They provide a possible source for icy bodies that enter the inner Solar System and are observed as comets. A possible scenario for the formation and dynamical evolution of icy objects under the influence of gas drag forces and gravitational scattering by proto-planets is briefly discussed. The outer Solar System plays the role of a corridor for interstellar matter entering into the Solar System. Further dust grains existing beyond Neptune's orbit are produced as ejecta of icy dust particles from the EKBOs due to the impact of interstellar dust grains. Their expected amount and lifetimes are examined. Compared to the extension of the region of planetesimals around the Sun, the region of influence of the solar wind extends to relatively small distances of the order of several hundred AU. But both complexes are coupled through the presence of interstellar dust that depends on the extension and the physical parameters of the heliosphere. The existence of a stronger solar wind in the early stages of the Solar System indicates that the heliosphere in a distant past might have been 10-100 times larger than the current one which possibly influenced the evolution of the planetary system. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.