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	Frequently Asked Questions Send to a friend  Printable version  En Español Keywords Solar System  Solar Wind  Astronomical Distances  Sun  Comets  Resources FAQs about The Solar System Solar System Guide Astronomy Gift Shop 2009 Sky Almanac McDonald Observatory logo cap How big is the solar system?  The Kuiper Belt (blue dots) may contain millions of icy comets beyond the orbit of Neptune. Pluto is one of its largest members. The farthest known object orbiting our Sun is a ball of ice and rock unofficially called Sedna, which lies about 10 billion miles away right now, although its highly elliptical orbit will carry it up to 84 billion miles from the Sun. Early measurements made from California's Palomar Observatory show that the object is probably 800 to 1,100 miles in diameter. Another hop, skip, and a jump takes us to the heliopause, where the stream of particles emitted by the Sun collides with the galactic gases of interstellar space, forming a so-called "bow shock." The boundary between the Sun's influence and interstellar space may lie as much as 15 billion miles ahead of the Sun's path through the galaxy, and more than 30 billion miles behind it. Farther still is the Oort Cloud, believed to be the source of extremely long-period comets (Hale-Bopp, for instance). This dark, incredibly cold region awaits interstellar travelers nearly six trillion miles away -- almost a quarter of the distance to the nearest star. Other FAQs Select FAQ category Earth, Moon, and the Sun The Solar System Space Probes and Human Exploration Stars and Nebulae Astronomers and Observatories Galaxies and Cosmology Stargazing and Star Lore » FAQs about StarDate Online The Solar System Links Center for Mars Exploration Solar System Exploration NASA's Mars Exploration Program Cassini Mission to Saturn Voyager Mission to the Outer Planets ESA Mars Express Messenger Mission to Mercury New Horizons to Pluto
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