How big is the solar system?
The farthest known object orbiting our Sun is a tiny ball of ice and rock called 1996 TL66, which lies more than 12 billion miles away at the farthest point in its orbit. (Pluto, at its farthest point, lies about 4.6 billion miles from the Sun.) This places it at the outer edge of the Kuiper Belt, a forest of comets from which Pluto's moon Charon (and perhaps Pluto itself) might have originated.
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.
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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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