Sedna, a planet-like object, is the most distant body in our solar
planet discovered so for and is probably the largest thing found in
the solar system since the discovery of Pluto in 1930.
First spotted using a modest 48-inch telescope by Caltech astronomers,
and then scrutinized by much larger scopes, Sedna is believed to have
a 10,500-year orbit around the Sun, and is presently about 13 billion
km away but should swing as far away as 130 billion km in its elongated
trajectory before returning toward the sun. At that extremity, Sedna
would be at a distance of about 900 astronomical units (1 AU=the distance
between Earth and sun).
Astronomers who have studied the object believe it is smaller than
Pluto and might represent the first object from the Oort Cloud to be
glimpsed. Long held to be the outermost preserve of matter in the solar
system, the Oort Cloud (or at least its inner edge) might be a bit nearer
than previously thought, if Sedna is indeed an Oort object. (NASA press
conference, 15 March.)