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M e r c u r y V e n u s E a r t h M a r s J u p i t e r S a t u r n U r a n u s N e p t u n e A solar system refers to a star and all the objects that travel in orbit around it. Our solar system consists of the sun - our star - eight planets and their natural satellites (such as our moon); dwarf planets; asteroids and comets. Our solar system is located in an outward spiral of the Milky Way galaxy. The Sun is the star at the center of the Solar System. It has a diameter of about 109 times that of Earth, and its mass accounts for about 99.86% Solar System. Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The Sun formed about 4.567 billion and it will live up to about 10 billion years old. An interesting Video made by NOVA in PBS will teach more facts: Secrets of the Sun The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals, such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. The four outer planets, or gas consist overwhelmingly of hydrogen and helium. All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. Interactive Universe Dwarf planets are not able to clear their orbital path so there are no similar objects at roughly the same distance from the Sun. A dwarf planet is much smaller than a planet (smaller even than Earth's moon), but it is not a moon. Pluto is the best known of the dwarf planets. NASA List of Dwarf Planets Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the sun for millions of kilometers. Explore the Solar system