h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Although it's probably not what everyone was looking for, they've found a tenth planet a bit smaller and a bit redder than Pluto . The jury is out as to whether it's a new planet....
If it is, then we'll be looking for an 11th planet , as the gravitational pull of Sedna is never going to explain Neptune's weird orbit....

Oh, and by the way, Sedna is twice as far from the Sun as Pluto. How on Earth did they find it, and how can they tell they just haven't missed other possible planets???

Also, why is it called Sedna - can't we call it Rupert after the discoverers parrot?

Do we really want a planet called Rupert? I think it is interesting that the existence of this planet is being talked about now.They have probably known about it for years, since it already has a name.Having said that, it is fairly momentous that a planet has been discovered in my lifetime. My son thinks they should call it after him!(I reiterate, do we really want a planet called Rupert?)

I think that there's probably a shedload of planets out there that we just haven't seen yet. When I wrote the original article, we didn't have telescope that could make out the likes of Sedna. now we do, and soon we'll have bigger and better ones that can see even further. This looks like an exciting time.

I think the real problem is that no one ever decided what a planet is, as when the first few were found not much was known about their structure or anything like that.

Now that we've found that our simplistic " goes around , orbits " view is not suitable if you've got a really big telescope and want to put everything in a group, we don't know what to do.()

Maybe one day they will find a massive planet which leads to the eccentricity in Neptune's orbit, but for the moment I don't see any harm in calling something out there Rupert - how about a comet...

I think that the eccentricity in Neptune's orbit is actually well accounted for, though I can't remember how. I suspect it might be due to the planets migrating over time: they were a lot further out, but they tend to migrate inwards towards the sun due to exchange of angular momentum with smaller bodies, which explains how the stuff from the Kuiper Belt got there.
On the subject of which, there appears to be a sudden 'drop-off' in the density of the Kuiper belt once one gets a certain distance out, which seems to suggest *another* large body, about the size of Earth, orbiting and mopping up straggling KBO's. So there might even be eleven planets, not counting Pluto and Sedna.

OK, so there may not actually be a massive object pulling Neptune's orbit so that it's wonky, but the belief that there could have been such an object was what led to the discovery of Pluto as astronomers searched for it.
====> It's always nice to have a reason to look for a new .

It is possible for there to be several undiscovered planets out there somewhere, but they may be labelled as TNO's as we may not be able to make out their size or shape. Then we'd just have to wait for bigger telescopes to have a closer look...

Unlike all the other planets this was named after an Canadian and Greenlandic Inuit Sea Goddess The legend of Sedna. Sedna was a beautiful Inuit hunter’s daughter, who refused to marry the man her husband chose for her. Her father said she might as well marry their dog. She did! Shocked, the father marooned her on an island and, when he found the dog had been swimming out to her with supplies, drowned the poor animal. But not before Sedna had had children, both human and canine.These children became the native Americans (humans) and the white men (dogs). Sedna was later kidnapped by a birdman and then rescued by her father, only for dad to throw her overboard when the birdman came after them, and to chop her fingers off to stop her getting back in the kayak . These fingers became seals, walruses and other sea mammals. As she drowned, Sedna became the sea-goddess and rejoined her dog- husband. She also later used her waves to drown her dad.
Sedna was discovered many years ago, but nobody actually could prove its existence. It is the 10th furthest from the sun.
before it wasnt discovered as it has a unusual orbit and has been hiden behind the sun so there could be even more lurking round the corner