Astronomers discover 'new planet'

[emad]

By Dr David Whitehouse
BBC News Online science editor


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.
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. Sedna, or 2003 VB16, 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.
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.

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. 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.


KUIPER BELT OBJECTS
Icy planetary bodies that orbit beyond Neptune in the distant region of the Solar System More than 400 such objects are currently known
They are believed to be remnants of the formation of the Solar System and among the most primitive objects available for study
In 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. The importance of Sedna is that it could be the first such world discovered in its normal orbit. Other similar though smaller worlds, like Quaoar and Varuna, originated in the KB but have since been perturbed into different orbits. More follow-up observations are being carried out by the Hubble Space Telescope and the Gemini Observatory. 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.


From: http://news.bbc.co.uk/1/hi/sci/tech/3511678.stm

Sedna: Icelandic fertility goddess....

[whistle]

1. Neat, I like the name Sedna also...

...what kind of God was Pluto?

[trotsky]

3. God of the Underworld, I believe...

n/t

[khashka]

2. Cool! But...

my first response was Kuiper Belt Object.

But I guess we'll have t wait and see :)

Khash.

[mrfrapp]

5. Kuiper Belt Objects

"my first response was Kuiper Belt Object."

It is a Kuiper Belt object -- as is Pluto incidentally. The argument is whether or not it should be categorised as a planet. My personal opinion is that is shouldn't; which would bring into question the current categorisation of Pluto.

To those who do think that Sedna is a planet, why isn't Charon a planet? It's the same size as this new object after all and only marginally smaller (in planetary terms) as Pluto. Thoughts?

[NNadir]

6. I'm perfectly comfortable calling Pluto a planet, if only because calling

it so may tend to increase study of this interesting system, i.e. the Pluto/Charon system.

I suppose it really comes down to a matter of semantics. One could set criteria such as size, history, age(to the extent known), shape (Pluto and Charon are round but other objects are not) or orbital parameters (Pluto orbits outside the plane of the other planets) to define what is and is not a planet. Of course the discussion of how to do this will start from the question one is trying to resolve: Is Pluto a planet. Obviously the selection of criteria itself would go one way or the other based on where one's feelings about Pluto start.

Certainly the existence of Kuiper Belt objects renders Pluto's claim to planethood somewhat suspect, but can we say that the existence of asteroids make the planethood of other objects suspect?

A similar argument can of course be applied to what does and does not constitute a moon. Does Saturn have 31 moons or billions of moons? Are Deimos and Phoebos moons or are they asteroids captured by Mars?

What about earth? Are all of those satellites moons or is there just one moon? After all, our current understanding of the origin of big moon on which we landed a few time assumes that it, like the newer moons, was launched from earth, albeit after a massive collision.

[sandlapper]

7. Planet vs. Kuiper Belt Object

As I understand it a planet orbits the sun, a Kuiper Belt Object does not. Technically this would make Haley's Comet not truly a comet, which follows a parabolic orbit.

[phantom power]

8. no, Kuiper belt objects orbit the sun.

So does Halley. Halley's orbit is elliptical. A parabolic trajectory is not an orbit: it's a flyby, as is a hyperbolic trajectory.

[khashka]

9. I really didn't mean to be controversial

I meant Kuiper Belt Object as opposed to a planet. I know the definitions are a little inexact.

I just thought it sounded more like an orbiting hunk o' rock or a bit of solar system flotsam than a real planetary object. But I don't know - I haven't seen the data and I'm a sociobiologist not an astronomer.

But I do find it intriguing....

Reviving the Charon issue is a good move. It's always pissed me off. There are some good reasons to believe there is a tenth planet. Charon seemed like a good bet. But if not, then Sedna.

I don't really have an axe to grind here. Just hey, lets find out more!

Khash.

[NNadir]

10. You weren't being controversial. You asked a good question.

It comes up all the time.

[flaminbats]

11. This means that there must be either seven planets or at least ten...

If we exclude Sedna...then logically Pluto and Mercury must also be excluded. Why include Mercury just because it isn't a Kuiper Belt object? Why exclude Pluto and Sedna because they're in the Kuiper Belt?

After all, the Kuiper Belt still counts as part of the solar system.

[rogerashton]

4. Sedna --

Inuit, not Icelandic.

Storms and vengeance, not fertility.

http://www.hvgb.net/~sedna/story.html

[emad]

12. Sedna: Inuit Ocean Goddess:

definition from UK BBC