Short-term unstable libration about , and transitions to horseshoe orbits are also possible. Other possible orbital interactions include libration and co-orbital configuration. There are several classes of co-orbital objects, depending on their point of libration. However, due to the Moon's libration, Earth does perform a slow and complex wobbling movement. These approaches moved Tempel 1 into its present libration around the 1&colon;2 resonance with Jupiter. This libration could have provided Enceladus with an additional heat source. This is referred to as "longitudinal libration". The study was conducted inside the interval where libration happens. Libration (from the Latin verb "librare" "to balance, to sway"; cf. Over time, some parts of the far side can be seen due to libration. About 18 percent of the far side is occasionally visible from Earth due to libration. This libration can be stable for less than 100 million to billions of years.