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
History of Mars observation about which the planet moves at a uniform rate of rotation. He proposed that the order of the planets, by increasing distance, was: the Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, and the fixed stars. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection "Almagest", which became the authoritative treatise on Western astronomy for the next fourteen centuries. In the 5th century CE, the Indian astronomical text "Surya Siddhanta" estimated the angular size of Mars as 2 arc-minutes (1/30 of a degree) and its distance to Earth as 10,433,000 km (1,296,600 yojana, where one yojana