With various space craft either having already flung themselves through Jupiter's space or missions currently under planning, there has been a good deal of study done on one of its most notable moons: Europa. For years, scientists have struggled with the idea of the small moon harboring a vast liquid ocean beneath its icy crust. Observations published in today's issue of the journal Nature have taken scientists another step closer to proving the theory.

One of the reasons Europa has been and continues to be such a hot spot for planetary scientists is that rumors of liquid water on any extraterrestrial body are soon followed by thoughts of extraterrestrial life. Since life as Earth knows it is based almost exclusively on the availability of water, scientists expect it to be the best bet for life having found a handhold on any other astronomical body.

The new telltale evidence of large body of liquid on Europa lies in a phenomenon called "true polar wander." Any spinning body, planetary or otherwise, tends to want to keep its heaviest areas at the outside of its physical body due to centrifugal force. While this phenomena is thought to affect many other planetary objects, including Earth, observations of the moon's exterior have given scientists cause to estimate that the old polar regions have shifted an incredible 80 degrees towards its equator.

Scientists used photo evidence gathered by various space probes that have meandered through Jupiter's system, Galileo, Voyager and New Horizons, to make the estimate. The scientists observed what are believed to be large stress fractures along the surface of Europa that fall in line with what are expected from a shift of such magnitude. It is likely that a buildup of ice at the poles ultimately caused the dramatic shift to take place.

The researchers say that it is possible to attribute the shift and such large fractures to the existence of a liquid water ocean beneath the surface of ice. The ocean would decouple the outer crust from an inner core, allowing a massive amount of wander for the ex-polar regions. A subterranean ocean of that size in a small ice ball revolving around a planet would likely be kept liquid by heat generated from the massive tidal forces of Jupiter's gravity.

One of Saturn’s moons, Enceladus, has also piqued the interest of exploration scientists, owing to its gigantic ice geyser, which spews particles outward to a distance of three times the moon's own diameter. The active geyser indicates an active interior and infers the large possibility of liquid water below its surface.

Though it may not be life as humans are familiar with, the presence of liquid water and the heat to keep it that way make moons like Europa and Enceladus prime candidates for life that didn't start on Earth. Bacteria that can survive such conditions -- lack of sunlight, extreme pressures, and strange chemical compositions -- are not unknown, but finding them or any other life on a foreign solar system body would probably be the discovery of the century.