The Role of Non-Gravitational Forces in Decoupling Orbits from Jupiter

There are many near-Earth objects (NEOs) with aphelia sufficiently sunward of 5 AU to be protected from close approaches to Jupiter. Such NEOs may derive either from the main asteroid belt or from an intermediate cometary source such as the short-period family, and at least two have exhibited comet-like physical activity. If a long-lived NEO is to arrive through this cometary avenue, then a mechanism is required to decouple its orbit from Jupiter. This may be achieved by gravitational perturbations alone, but a long timescale is required. Attainment of such a cis-Jovian orbit is feasible rather more rapidly, and with a higher efficiency, if non- gravitational forces also are acting. Here we discuss the role of such forces in producing NEOs from Jupiter-family comets.