Therefore, even though Enceladus is only Saturn's sixth-largest moon, it is amazingly active. Because of the success of the Cassini mission, scientists now know that geysers spew watery jets hundreds of kilometers out into Space, originating from what may well be a vast subsurface sea. These jets, which erupt from fissures in the little moon's icy shell, whisper a siren's song to bewitched astronomers. This is because the jets suggest that the icy moon may harbor a zone where life might have evolved. The jets dramatically spray water ice from numerous fissures near the south pole, that have been playfully termed "tiger stripes." The "tiger stripes" look like giant scratches made by a tiger's raking claws. A billion years ago, our Moon was closer to Earth than it is now. As a result, it appeared to be a much larger object in the sky. During that ancient era, if human beings had been around to witness such a sight, it would have been possible to see the entire Moon--not merely the one near side face that we see now. A billion years ago, it took our Moon only twenty days to orbit our planet, and Earth's own day was considerably shorter--only eighteen hours long. Stupendous, almost unimaginably enormous tides, that were more than a kilometer in height, would ebb and flow every few hours. However, things changed, as the lunar orbit around our primordial planet grew ever wider and wider. Annually, Earth's Moon moves about 1.6 inches farther out into space. Currently, the lunar rate of rotation, as well as the time it takes to circle our planet, are the same. The team of scientists used data gathered by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, composed of a duo of twin spacecraft that circled Earth's Moon throughout 2012, each measuring the push and pull of the other as an indicator of lunar gravity.