Why are the inner and outer planets so different?
The rocky, terrestrial planets — Mercury, Venus, Earth, and Mars — all formed in the inner, hotter part of our Solar System. It was so hot that volatile materials — materials that evaporate easily at normal temperatures and pressures – could not condense. Much of the gas and ice in the solar system could not exist as solids at the high temperatures in the inner region. However, metals and silicates could withstand the high temperatures and these materials became concentrated in the inner solar system. It was from these heavier materials that the rocky inner planets were made. In the outer, cooler portion of the Solar System more volatile materials such as water ice, other ices, and gases were able to accumulate onto the giant planets. Our outer gas giant planets — Jupiter, Saturn, Uranus, and Neptune formed from these materials. These planets have small icy rocky cores surrounded by thick accumulations of gases. What about Pluto? Tiny rocky icy Pluto lies beyond the gas giants. Some sc
