Solar System largely of materials with lower melting points. The boundary in the Solar System beyond which those volatile substances could condense is known as the frost line, and it lies at roughly 5 AU from the Sun. The objects of the inner Solar System are composed mostly of rock, the collective name for compounds with high melting points, such as silicates, iron or nickel, that remained solid under almost all conditions in the protoplanetary nebula. Jupiter and Saturn are composed mainly of gases, the astronomical term for materials with extremely low melting points and high vapour pressure, such as hydrogen, helium,
Solar eclipses on Jupiter the variations were caused by the varying distance between Earth and Jupiter as the two planets moved in their orbits around the Sun. Spacecraft can be used to observe the solar eclipses on Jupiter; these include "Pioneer 10" and "Pioneer 11" (1973 and 1974), "Voyager 1" and "Voyager 2" (1979), "Galileo" orbiter (1995–2003), "Cassini–Huygens" (2000) and "New Horizons" (2007) observed the transits of their moons and its shadows. The mean angular diameter of the Sun as viewed from Jupiter is 372 arc-seconds, or 6' 12" (about that of the Sun as viewed from Earth), varying slightly from 381" at perihelion