Astronomers have detected what could be the Solar System's 10th planet.

It was first seen by astronomers using California's Mount Palomar Observatory, and has been given the name "Sedna" after the Inuit goddess of the ocean.

Observations show it measures about 1,180-2,360km (730-1,470 miles) across, making it similar in size to Pluto.

Astronomers now say they have evidence that Sedna has its own moon, although this needs to be confirmed, and is also very red in colour.

There is likely to be some debate about whether it qualifies as a true planet, but some scientists are already saying it re-defines our Solar System.

Further than Pluto

Sedna, or 2003 VB12, as it was originally designated, is the most distant object yet found orbiting our Sun. It is three times further away than Pluto (average distance to the Sun is 5.9 billion km or 3.6 billion miles).

It was discovered using the Mt Palomar facility in November by astronomers from the California Institute of Technology, Yale Observatory and the Gemini Observatory.

Dr Mike Brown of the California Institute of Technology, US, leader of the research team that found the body, said he did not believe it was a true planet.

He suggested this "planetoid" is about half rock and half ice mixed together, but further work is needed to verify this.

The scientists say that its rotation on itself is relatively slow, suggesting it could have a satellite in orbit around it.

Follow-up studies by the Tanagra Observatory have measured the thermal radiation coming from Sedna to determine how hot it is, and therefore provide some estimate of its size.

Researchers believe that Sedna's surface temperature is about -240 degrees Celsius (-400 degrees Fahrenheit).

Click here to see Sedna's size and distance from the sun

This estimate is uncertain but the object is likely to be between half the diameter of Pluto (2,360km or 1,470 miles) and Pluto's size; though some astronomers think it could be larger than the ninth planet itself.

From the observations made so far, astronomers have determined Sedna's orbit to be a very large one.

It is currently 90 times the Earth-Sun distance away (149 million km or 93 million miles), but its orbit can take it 10 times further away still.

Small worlds

Although Sedna could be a so-called Kuiper Belt object, its discoverers are unsure if it is as they consider it to be unlike any other object yet found.

The KB contains hundreds of known objects and astronomers believe there are many more awaiting discovery. Most are small worlds of rock and ice but some could rival Pluto in size.

n recent years, astronomical work has thrown up several big objects. Quaoar, found in 2002, is about 1,200km (745 miles) across. Ixion, discovered in 2001, is 1,065 km (660 miles) wide. Varuna, detected in 2000, has a diameter of approximately 900 km (560 miles).

And only in February this year, scientists picked up the object 2004 DW, which is though to be 1,800km (1,120 miles) across.

Is it a planet?

The new discovery will reignite the debate about what constitutes a planet.

One group of astronomers believe that Pluto is not a true planet but merely one of the largest of a vast number of minor objects in the outer Solar System.

The alternative standpoint is that Pluto is a planet and those who believe that will have to classify Sedna as the 10th planet.

The name Sedna has been provided by its discoverers.

However, if its planetary status is confirmed, it may be that astronomy's governing body, the International Astronomical Union, will want to reconsider this, to make it more consistent with the mythological names of other planets.

Source

that article is old, but the official confirmation was only made today

One of the questions that is going to have to be asked is this:

What costitutes a planet in the strictest sense? Needs to be answered so that clarifcation can be made easier

Another question this raises is this:

How far does the limits of our solar system reach before something can be classified as extra-solar?

Whether it orbits around the Sun, I guess ... if it does, then it's part of the Solar System.

not like this is an importaint comment or anything, but since pluto is said to be a comet, tecnicaly this "10th planet" is actualy the ninth.

Well, Pluto is supposed to have been a comet that was knocked out of it's usual orbit and into a smaller one around our sun- converting it into a "planet".

the planet 2003.... is not sedna and is 1 and a half plutos in size

At present, there are four basic categories of objects that inhabit our solar system. Here's a list of definitions for these categories that will set the stage for deciding whether Pluto has been mis-classified.

Comet
These objects are the sometimes spectacular visitors to the inner solar system but usually spend most of their time in the furthest reaches of the solar system. They are very small bodies, not usually any bigger than 10 km or so. Despite their very small size, they create huge spectacles when they get close enough to the Sun to release water from their surface. This water escapes immediately into space and usually carries some dust or dirt along with it. This material leaves huge tails and streamers in the sky.

Asteroid
These objects are found and known in great abundance in our solar system and most of them inhabit the "asteroid belt" found between Mars and Jupiter. Some of the known asteroids wander in as far as Venus or Mercury and a new batch has recently been recognized out well beyond the orbit of Pluto. Asteroids are small, irregularly shaped objects, that have inert and airless surfaces.

Satellite
This class of object is perhaps the simplest. If the object orbits another larger object, then it is considered a satellite. These bodies can, and do, span a great range of sizes and properties including those shared by all the other categories.

Planet
A planet is a special term applied to the larger members of our solar system. Rule #1, a planet must orbit the Sun. Rule #2, it must be large enough that it's own gravity is strong enough to maintain a spherical shape. There are certain properties we expect to see in a planet such as an atmosphere and dynamic and active surfaces at some stage in their history.
In the end, these definitions are useful only if they provide useful labels that collect objects of similar properties together. Trying to stuff Pluto into the Comet bin would clearly be wrong. Pluto is far too big to behave anything like the tiny chunks of ice we call comets. Could Pluto be considered an asteroid? Well, you might be tempted because Pluto is so small. But consider the fact that Pluto has enough gravity to be spherical and retain a significant atmosphere. It also probably has an active surface and very pronounced seasons. These characteristic sure do make it sound more like the other planets.

I have to agree, XSAS- the gravity to retain an atmosphere is a key factor- though I do believe I recently read that a few of Jupiter's and Saturn's Moons have thin atmospheres of their own.

I'll see if I can find the magazine.

Yes, I have been following this story too.... I have heard that this planet is a large planet, much larger than pluto, it seems so far away, surface temp of -400 fahrenheit..... like that could ever support life.... Interesting story. I havent heard that pluto was claimed to be a comet...a comet has that tail on it and a comet moves alot faster than pluto has been tracked too. It's just strange to me that in our small solar system we are the only planet with life..... there has to be solar systems out there with like 10 planets with like life on 5 or more...I would think...we cannot be alone

Yes i have read about there being a 10th planet in our solar system they have named this planet XENA yes after the warrior princess, that is why i think the jornalist was having ago at the poor scientists for naming the planet, if it is one that is !

But like i have always said maybe these planets are there for a reason, like humans have lived on them run out of fuels,water,plants etc. and have found some sort of why of moving to another planet....
But thats just what i am thinking i know it sounds crazy

But i also think that for example..adam and eve were in the garden of eden was this not the planet Venus or somthing....

Anyways this planet may change the course of our thinking.....

Dude that's one old article. There have been more since then. Sedna was actually classified as a Trans-Neptunian Object, I think, but definately never classified as a Planet.

This is the newest "10th" Planet...

http://en.wikipedia.org/
http://www.nasa.gov/
http://skyandtelescope.com/
http://www.msnbc.msn.com/
http://www.space.com/

It's called 2003 UB313 - It is still under debate whether or not they will classify it as a Planet or not. It is approx. 1.5X the size of pluto and has a highly inclined orbit with an offset of 44°. Currently in the constellation of Cetus.



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I hereby volonteer to go on the first space ship to this new planetoid.

One could say that our solar system extends as far out as the end of the Oorts cloud, which is pretty far out, some 3 light years or so That is at least as far the physical and gravitational influence extends.

My dad thinks that planet's Niburu(you know, that one that comes close to earth every 3500 years and where aliens come from? Yeah that one ) I tried telling him that Niburu is a dumb theory, but he insists the show he watched was very "informative"

Oh yeah, didn't they take Pluto off the official list of planets? I read about it somewhere, but forgot where

Nope. The International Astronomical Union would deal with something lilke that. They have a page regarding that.... Pluto



Here's what they have to say abotu the latest "Planet" 2003 UB313

http://www.iau.org/IAU/FAQ/2003_UB313.html

Pluto will probably always be seen as a planet as it is the only confirmed planet to be discovered by an american

So basically it is not a planet because it is farther than 40 AU? Want to verify it because my english might lie to me. And why has this not been on the news? Planet or not this would still be news to most people I think...

No, its a planet....it revolves around our sun, they said takes 560 earth years to complete 1 complete rotation..... Just another frozen planet out in space doing nada!!!

What I take of that is that they are going to review their current definition of the word "planet".