What is Sedna?
Sedna is a solar orbiting object about 1800km across, at an average distance of 400 A.U., that nearly got categorized as the tenth planet. For an excellent website on Sedna, see http://www.gps.caltech.
Sedna, formally called 90377 Sedna, is a newly discovered planetary body estimated to be about half the size of Pluto. It takes about 12,000 years to make a complete orbit around the Sun and is categorized as a trans-Neptunian object, like Pluto. It is a red planet, nearly as red as Mars, and at the time of its discovery was the most distant planetoid in the solar system. Sedna was discovered in late 2003 at the Palomar Observatory, near San Diego, California. Since then, several other objects of similar size and distance from the sun have also been detected, including the planetoid Xena, which is likely larger than Pluto. The orbit of Sedna is highly elliptical, like most outer solar system bodies. At its furthest out, Sedna is estimated to be almost a thousand times as distant from the Sun as the Earth is. At its closest, it is only about 76 times as distant. The existence of Sedna and similar objects has led scientists to believe that there may be dozens of other objects of the same
The movie loop above shows a small patch of sky (6.2 by 2.4 arcminutes) on a sequence of four nights. The object moving down and to the right across the center of the field is called Sedna (90377). Discovered with the 48 inch Palomar Schmidt Camera just over one year ago by M. Brown, C. Trujillo, and D. Rabinowitz, Sedna is the furthest solar system object known. At a current distance of 88 AU it is about three times the distance of Pluto. As with asteroids, the apparent motion from night to night is largely a response (called parallax) to the earth’s own orbital motion. However, the angle nearby asteroids move in an hour takes the more distant Sedna an entire day. It is estimated to be between 1300 and 1800 km across, compared to about 2 km for asteroids of similar apparent brightness (300,000,000 times more volume!). Why is Sedna important? Sedna is in an elliptical orbit, bringing it as close as 76 AU to the sun and as far as 930 AU. Hence, at its closest approach it is still outsid
