Solar System the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that
The 50 Most Extreme Places in Our Solar System The 50 Most Extreme Places in Our Solar System The 50 Most Extreme Places in Our Solar System is the title of a science book by David Baker, professor of physics at Austin College and Todd Ratcliff, a planetary geophysicist at the Jet Propulsion Laboratory. The book is divided into nine sections with a few chapters in each section. The divisions are roughly phenomenological. The book is currently available in two translations with a third in progress. Reviews have been positive including being awarded Honorable Mention in Cosmology and Astronomy in the 2010 PROSE Awards and named an Outstanding University