Is it true there is an extra planet? I believe they said we have not
discovered it yet because it was hiding behind Mars.

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Request for Question Clarification by sublime1-ga on 15 May 2006 17:05 PDT

samdaman...

This report indicates that a tenth planet has been discovered:
http://www.solarviews.com/eng/tenthplanet.htm

Let me know if this satisfies your interests...

sublime1-ga

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Clarification of Question by samdaman-ga on 16 May 2006 10:37 PDT

Cool...but they have not named it yet :( Thats very interesting,
because it means that there is definitely more out there we still need
to discover. I understand now that it would be impossible for anything
to be hiding behind another planet due to individual orbits. Thanks a
lot, you've been a great.

samdaman...

Thanks for confirming your satisfaction with the information
you've received. I'll repost my remarks here, for the sake of
future readers, and to finalize the answer.

-------------------------------------------------------------

This report indicates that a tenth planet has been discovered:
http://www.solarviews.com/eng/tenthplanet.htm

sublime1-ga

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Request for Answer Clarification by samdaman-ga on 18 May 2006 13:35 PDT

Have they name it yet?

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Clarification of Answer by sublime1-ga on 18 May 2006 14:12 PDT

"Because of its frigid temperatures, the team has named the
 object Sedna, after the Inuit goddess of the sea from whom
 all sea creatures were created."
http://www.gps.caltech.edu/~mbrown/sedna/

However, that's somewhat of a pet name, created by the team.

"The real name of the new planet is currently in limbo while
 committees decide its fate."
Other nicknames and more on the page:
http://www.gps.caltech.edu/~mbrown/planetlila/

A committee is currently deciding whether it even fits the
definition of a planet:
http://www.gps.caltech.edu/~mbrown/planetlila/#name

sublime1-ga

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Request for Answer Clarification by samdaman-ga on 22 May 2006 12:20 PDT

So there is possibly no "extra planet"??? This question will clear up
an argument if you can be clear as to whether or not there is an extra
planet? I mean if it has not been named yet its hard say it exists as
an extra planet in the known universe...not that there is much in a
name, but it would help. I like Sedna.

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Clarification of Answer by sublime1-ga on 22 May 2006 13:30 PDT

samdaman...

Read the links I gave you, specifically the section titled,
'Is this object really a planet? Is Pluto a planet? What makes a planet?'
and 'How will the planetary status be decided?', on this page:
http://www.gps.caltech.edu/~mbrown/planetlila/

They answer your question as well as it can be answered. In short:
Scientists have come to realize that, scientifically, Pluto is 
different from other planets, but culturally, it's long been
acknowledged as a planet. To resolve this, scientists have (by
a thin margin) voted to define a planet as the current planets
plus celestial objects like Pluto and anything bigger. That's
the current official stance. Here's the quote from the page:

- A special committee of the International Astronomical Union
  (IAU) was charged with determining "what is a planet."
- Sometime around the end of 2005, this committee voted by a
  narrow margin for the "pluto and everything bigger" definition,
  or something close to it.
- The exectutive committee of the IAU then decided to ask the
  Division of Planetary Sciences (DPS) of the American Astronomical
  Society to make a reccomendation.
- The DPS asked their committee to look in to it.
- The DPS committee decided to form a special committee.
- Rumor has emerged that when the IAU general assembly meets in
  August in Prauge they will make a decision on how to make a
  final decision!

Sedna is bigger than Pluto, so, by the current definition, it
is a tenth planet. This doesn't mean that a committee of scientists
can't eventually change their minds, and how they choose to define
a planet. They may eventually decide to reject their current 
definition and rule that Pluto and similar objects are not planets
and let the cultural chips fall where they may. Or they may evade
the decision process and hope it all goes away. If they decide
to maintain the current definition, then they'll form another
committee to name the tenth planet officially.

But for now, Sedna is a planet with unofficial pet names.

sublime1-ga

The answer has met every one of my curious needs.

I have read that there is speculation that there may be another planet
further away than Pluto.  But there is also discussion that maybe
Pluto should not be considered a planet but rather just a object in
the Kuiper Belt.
http://en.wikipedia.org/wiki/Kuiper_belt

It would be impossible for a near-sun planet to "hide" behind Mars.

I was going to list some of the "extra planets", but this is much
better - http://www.nineplanets.org/hypo.html

Ian G.

Missed one! http://en.wikipedia.org/wiki/Counter-Earth

Ian G.

"I believe they said we have not discovered it yet because it was
hiding behind Mars."

   An orbiting planet in space couldn't stay hidden behind another
planet as seen from Earth. If it were on an entirely independent
orbit, then being at a different distance from the Sun it'd have a
different orbital period, and so would eventually fall out of
alignment with Mars & Earth. It would be in line of sight most of the
time. Were it a satellite with Mars (a "moon"), then its orbital
period would take it all the way around the planet in so short a time
as to be in plain sight most of the time.

Both Sedna and the dual moons Pluto-Charon are Kuiper Belt (or
potentially Oort Cloud) escapees which explain their wildly different
orbits. Sedna's orbital period is 4,401,380 days. Compare to
Pluto-Charon's 90,613.3 day and Earth's 365.25 day orbital periods.
Also, this is a good image to understand the scope of Sedna:
http://upload.wikimedia.org/wikipedia/en/7/77/Trans-Neptunian_object_2003_VB12.Sedna.orbit_comparisons.jpg
One of the reason's for the recent (3 years ago) discovery is that
Sedna is nearing it's closest approach to Sol.

10th planet? KBO 2003UB313 is larger than pluto. We're witing for the
IAU to release the definition of a planet this month and the next.
Meanwhile, it's been nicknames Xena

But Pluto might be called a big rock and dropped from the list of Solar planets.