The Kuiper Belt

More and more objects are being found in the Kuiper Belt, out beyond the planet Neptune.  Some of them are quite large -  over 2,000 kms in diameter.  Paired objects are also quite common, some of the pairs are only loosely bound by gravity.  Some of these observation pose difficulties for the standard theories of Solar System formation.  See Kuiper Belt may be born of collisions  at Nature.