Interstellar comet

An interstellar comet is a comet (or exocomet) located in interstellar space, and not gravitationally bound to a star. Besides known comets within the Solar System, or known extrasolar comets, no interstellar comet, not gravitationally bound to a star, has been conclusively identified. Nonetheless, such comets are conjectured to exist: gravitational scattering by planets and passing stars has ejected many Oort cloud comets from the Solar System, and the likelihood of similar processes in extrasolar planetary systems suggests the existence of a large population of unbound cometary bodies. At present, an interstellar comet can only be detected if it passes through the Solar System, and could be distinguished from an Oort cloud comet by its strongly hyperbolic trajectory (indicating that it is not gravitationally bound to the Sun). Comets with weakly hyperbolic trajectories have been observed, but the trajectories of these comets are consistent with having been knocked loose from the Oort cloud and do not indicate an origin in interstellar space. The most eccentric known comet, C/1980 E1, only has an eccentricity of 1.057, far less eccentric than an interstellar comet would be expected to be.