Sedna: Planetoid or Planet?

On March 15, 2004, astronomers confirmed the discovery of the most distant object ever identified in our solar system. Twice as far from the Sun as any known object, this red mass has an unusually elliptical orbit that takes a staggering 10,500 years to complete. Officially called 2003 VB12, its discoverers claim that it is the first known object from the long-hypothesized Oort Cloud, believed to be home to billions of frozen comets. The object's surface temperature is about minus 400°F (minus 240°C). Its frigid celestial homeland inspired its informal name, Sedna, the Inuit goddess of the icy northern oceans. In addition to its unparalleled coldness and distance, Sedna also distinguishes itself as the largest object identified since Pluto's discovery in 1930. About three-quarters of the size of Pluto, it is considered a planetoid (a minor planet or asteroid). Thought to be composed of rock and ice, it has a reddish hue similar to that of Mars.

In this artist's visualization, the newly discovered planet-like object, dubbed "Sedna," is shown where it resides at the outer edges of our solar system. The object is so far away that the Sun appears as an extremely bright star instead of the large, warm disc observed from Earth. All that is known about Sedna's appearance is that it has a reddish hue, almost as red and reflective as the planet Mars. In the distance is a hypothetical small moon, which scientists believe may be orbiting this distant body. Photo courtesy of NASA

Beyond PlutoThe Solar SystemA Tenth Planet?

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