The past and future motion of Comet P/Swift-Tuttle

The orbit of P/Swift-Tuttle is investigated by way of a long-term integration forward to AD 2392 and backward to 703 BC. Two of its previous returns prior to the telescopic period, in AD 188 and 69 BC, are identified in Chinese records. No other observations of P/Swift-Tuttle have been found. The non-gravitational forces that affect the motion of most active comets appear to be negligible for this comet, suggesting that either the comet outgasses radially toward the Sun and in a symmetric fashion about perihelion and/or it is far more massive than periodic comets of comparable activity (e.g. P/Halley). Our successful integration is consistent with all the observed returns of the comet