Magellanic Clouds
Models describing the formation of the Magellanic Stream had been produced since 1980. Following computing power, the initial models were very simple, non-self-gravitating, and with few particles. Most models predicted a feature leading the Magellanic Clouds. These early models were 'tidal' models. Just like tides on Earth are induced by the gravity of the 'leading' Moon, the models predicted two directions opposite each other, in which particles are preferentially pulled. However, the predicted features were not observed. This led to a few models that did not require a leading element but which had problems of their own. In 1998 a study analysing the full sky survey made by the HIPASS team at Parkes Observatory generated important new observational data. Putman et al. discovered that a mass of high-velocity clouds leading the Magellanic Clouds was actually fully connected to the Magellanic Clouds. So, the "leading arm" feature had its existence finally established. Furthermore, Lu et al. (1998) and Gibson et al. (2000) established the chemical similarity between the streams and Magellanic Clouds.