Sedna is a Trans-Neptunian Object. Here's what an artist thinks Sedna might look like.
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Image courtesy NASA/JPL-Caltech/R. Hurt (SSC-Caltech)
Trans-Neptunian Objects (TNO)
There are lots of small worlds at the edge of our Solar System. They are made of ice and rock. They are further away from the Sun than most planets. They are further away than the 8th planet, Neptune. They are called Trans-Neptunian Objects (or TNOs for short).
Some TNOs are only a little farther out than Neptune. They are in an area called the Kuiper Belt. It is sort of like the asteroid belt. They are called Kuiper Belt Objects (or KBOs for short). The planet Pluto is actually a Kuiper Belt Object. So is Quaoar.
Some TNOs are much, much further away. They are way out past Neptune. They orbit in an area called the Oort Cloud. Sedna might be from the Oort Cloud.
Some objects are in between the Kuiper Belt and the Oort Cloud. 2003 UB313 is a TNO that was discovered in 2005. Its nickname is "Xena". Xena might be bigger than Pluto. Xena has a strange orbit. Its orbit is in between a Kuiper Belt orbit and an Oort Cloud orbit.
Most comets come from the Oort Cloud and the Kuiper Belt.
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