Exploration of Jupiter reach Europa after a 6.5 year cruise. The spacecraft would fly by the moon 32 times to minimize radiation damage. Because of the possibility of subsurface liquid oceans on Jupiter's moons Europa, Ganymede and Callisto, there has been great interest in studying the icy moons in detail. Funding difficulties have delayed progress. The "Europa Orbiter" was a planned NASA mission to Europa, which was canceled in 2002. Its main objectives included determining the presence or absence of a subsurface ocean and identifying candidate sites for future lander missions. NASA's "JIMO" ("Jupiter Icy Moons Orbiter"), which was canceled in 2005, and
Origin of the Moon that two bodies—each five times the size of Mars—collided, then re-collided, forming a large disc of debris that eventually formed Earth and the Moon. The paper was called “Forming a Moon with an Earth-like composition via a Giant Impact,” by R.M Canup. A 2012 study on the depletion of zinc isotopes on the Moon supported the giant-impact origin for Earth and the Moon. In 2013, a study was released that indicated that water in lunar magma is indistinguishable from carbonaceous chondrites and nearly the same as that of Earth in isotopic composition. The giant-impact hypothesis was again challenged in September