Sedna is at present
over 90 AUs away ( An AU is an Astronomical Unit, The Distance of
the Earth from the Sun, 93 million miles ). Sedna is about 1,800
km in diameter, slightly smaller than Pluto and nearly 3 times as
far away. Its orbit is highly elliptical, passing closest to the
Sun at 75 AU. It orbits once every 12,000 years.
Its elliptical orbit means that it is only
detectable to us for a period of 60 years out of 12,000. This means
that there is only a 1 in 60 chance of seeing it, and that there
are possibly 60 or more Kuiper Belt objects of at least Sedna's
proportions. Only a half dozen or so of the newly discovered objects
are near Pluto's or Xena's proportions.