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The Solar System What’s in Our Solar System? Our Solar System consists of a central star (the Sun), the nine planets orbiting the sun, moons, asteroids, comets, meteors, interplanetary gas, dust, and all the “space” in between them. The nine planets of the Solar System are named for Greek and Roman Gods and Goddesses. Inner and Outer Planets Inner Planets: Mercury Venus Earth Mars Outer Planets Jupiter Saturn Uranus Neptune Pluto The Relative Size of the Planets in the Solar System The Sun The sun’s energy comes from nuclear fusion (where hydrogen is converted to helium) within its core. This energy is released from the sun in the form of heat and light. Remember: Stars produce light. Planets reflect light. A star’s temperature determines its “color.” The coldest stars are red. The hottest stars are blue. The 9 Planets of the Solar System Planets are categorized according to composition and size. There are two main categories of planets: small rocky planets (Mercury, Venus, Earth, Mars, and Pluto) gas giants (Jupiter, Saturn, Uranus, and Neptune) Characteristics of Small Rocky Planets They are made up mostly of rock and metal. They are very heavy. They move slowly in space. They have no rings and few moons (if any). They have a diameter of less than 13,000 km. Mercury Mercury has a revolution period of 88 days. Mercury has extreme temperature fluctuations, ranging from 800?F (daytime) to -270?F (nighttime). Even though it is the closest planet to the sun, Scientists believe there is ICE on Mercury! The ice is protected from the sun’s heat by crater shadows. Venus Venus is the brightest object in the sky after the sun and moon because its atmosphere reflects sunlight so well. People often mistake it for a star. Its maximum surface temperature may reach 900?F. Venus has no moons and takes 225 days to complete an orbit. Earth Earth is the only planet known to support living organisms. Earth’s surface is composed of 71% water. Water is necessary for life on E