AND

Secular changes brought about by tidal friction in the solar system are reviewed. The presence or absence of specific changes is used to bound the values of Q (the specific dissipation function) appropriate for the planets and satellites. It is shown that the values of Q separate sharply into two groups. Values in the range from 10 to 500 are found for the terrestrial planets and satellites of the major planets. On the other hand, Q for the maior planets is always larger than 6 X 104. Estimates of tidal dissipation i the atmos-pheres of the Jovian planets lead to values of Q which are consistent with those we have calculated on the basis of secular changes in the satellites ' orbits. However, it is difficult to reconcile these large Q's with the much smaller values obtained in laboratory tests of solids. Lyttleton's hypothesis that Pluto is an escaped satellite of Neptune is critically examined. Using the Q's we obtain for the major planets and their satellites, we show that any eccentricity that Triton's orbit may have possessed after a near encounter with Pluto would have been subsequently damped, thus accounting for its present near-circular orbit