it hard to see where one galaxy ends and the next begins. Tidal loops, where a tail joins with its parent galaxy at both ends, are rarer still. Satellite interactions Because tidal effects are strongest in the immediate vicinity of a galaxy, satellite galaxies are particularly likely to be affected. Such an external force upon a satellite can produce ordered motions within it, leading to large-scale observable effects: the interior structure and motions of a dwarf satellite galaxy may be severely affected by a galactic tide, inducing rotation (as with the tides of the Earth's oceans) or an anomalous mass-to-luminosity ratio. Satellite galaxies can also be subjected to the same tidal stripping that occurs in galactic collisions, where stars and gas are torn from the extremities of a galaxy, possibly to be absorbed by its companion. The dwarf galaxy M32, a satellite galaxy of Andromeda, may have lost its spiral arms to tidal stripping, while a high star formation rate in the remaining core may be the result of tidally-induced motions of the remaining molecular clouds (Because tidal forces can knead and compress the interstellar gas clouds inside galaxies, they induce large amounts of star formation in small satellites.) The stripping mechanism is the same as between two comparable galaxies, although its comparatively weak gravitational field ensures that only the satellite, not the host galaxy, is affected. If the satellite is very small compared to the host, the tidal debris tails produced are likely to be symmetric, and follow a very similar orbit, effectively tracing the satellite's path. However, if the satellite is reasonably large—typically over one ten thousandth the mass of its host—then the satellite's own gravity may affect the tails, breaking the symmetry and accelerating the tails in different directions. The resulting structure is dependent on both the mass and orbit of the satellite, and the mass and structure of the conjectured galactic halo around the host, and may provide a means of probing the dark matter potential of a galaxy such as the Milky Way. Over many orbits of its parent galaxy, or if the orbit passes too close to it, a dwarf satellite may eventually be completely disrupted, to form a tidal stream of stars and gas wrapping around the larger body. It has been suggested that the extended discs of gas and stars around some galaxies, such as Andromeda, may be the result of the