History of Solar System formation and evolution hypotheses moon and Mercury was a moon of Venus but drifted away because of the Sun's gravitational influence. Mars was a moon of Bellatrix. One major argument against exploding planets and moons is that there would not be an energy source powerful enough to cause such explosions. In J. Marvin Herndon's model, inner (large-core) planets form by condensation and raining-out from within giant gaseous protoplanets at high pressures and high temperatures. Earth's complete condensation included a c. 300 Earth-mass gas/ice shell that compressed the rocky kernel to about 66% of Earth's present diameter (Jupiter equates to about 300 Earth masses, which
History of astronomy Jupiter in 1610, which are now collectively known as the Galilean moons, in his honor. This discovery was the first known observation of satellites orbiting another planet. He also found that our Moon had craters and observed, and correctly explained, sunspots, and that Venus exhibited a full set of phases resembling lunar phases. Galileo argued that these facts demonstrated incompatibility with the Ptolemaic model, which could not explain the phenomenon and would even contradict it. With the moons it demonstrated that the earth does not have to have everything orbiting it and that other parts of the solar system could