Sedna

[mmcirvin]

Sedna is an object almost as large as Pluto and currently three times further out from the Sun, on an elliptical orbit with a period of 10,500 years that takes it wayyy the heck out into space at the other end. It may have a moon of its own. It seems to be the first observed member of the Oort Cloud, and since there are almost certainly more of those, some probably bigger than Pluto, it will undoubtedly fire up the "is Pluto a planet?" arguments again.

I vote for keeping the current list of nine, but stressing that the definition of "planet" is largely a historical accident, since it doesn't correspond well to any of the physically useful categories of objects in the solar system. Excluding Pluto would confine it neatly to the four largest terrestrial bodies in the inner solar system, and the four Jovians; but apart from upsetting Pluto's sentimental fans, that then raises the question of why we'd call two such disparate categories of object by the same name anyway.

Comments

[jmkelly.livejournal.com]

Eight. It's important for the people who "would get confused" by the change in number to learn that science means constant re-examination and revision.

I wrote more at http://www.livejournal.com/users/jmkelly/31068.html

You raise a good point about using the same word to designate gas giants and rocks, though.

[mmcirvin.livejournal.com]

The answer is definitely not to call Sedna the tenth planet. It's hardly much larger than the big Kuiper Belt objects that have been discovered recently, such as Quaoar, Ixion, Varuna, etc. There seems to be a continuum in sizes of these things with no big gap below Pluto. If some regular standard insists that Sedna needs to be designated a new planet, then there are a whole lot of new planets.

[mmcirvin.livejournal.com]

Here's an eccentric notion: "Planet" as historic landmark status.

From a public-outreach perspective, Pluto is nice to highlight because it's the first-known, biggest-known, and certainly easiest to see of the Kuiper Belt objects: the "king of the Kuiper Belt". So maybe it gets honorary planet status from that. But then we need to designate Sedna as a planet because it's the equivalent object for the "inner Oort cloud", and also Ceres and Chiron (king of the Centaurs, occasionally described as a tenth planet shortly after discovery) get planet status for the same reason, and... hmm, what else?

Some representative comet-- Halley, perhaps? Certainly it was the first whose status as a solar-system body was figured out. Comet Halley is the seventh planet (in discovery order); Uranus is the eighth! Then Neptune, Ceres, Pluto, Chiron, Sedna...

Hmm, if moons are counted as another category of solar-system object, then the Moon gets planet status as the historical King of Moons. Some people think it really ought to be considered a planet anyway, as the fifth of the large terrestrial inner-solar-system objects.

Or maybe, by the "historic landmark" criterion, we need to separately designate the four Galileans (the first of the big outer-solar-system satellites to be discovered), Phobos and Deimos (the epitome of little asteroidal moons), and the Moon (an anomaly unto itself)... hmm, this list is getting unwieldy.

[(Anonymous)]

My theory on about Pluto is that it's best understood as a minor stock character in a Regency Historical Romance. One of those distressingly pushy and vulgar creatures who somehow inveigled their way into being received by the ton due to their distant connection to one of their betters, and of course we all know gentlemen often have a low taste for _that_ sort of trans-neptunian object. But then the Marquis actually offering marriage! And the creature actually accepting! Scandalous!

As for what they get up to behind closed doors with that sister Chiron...Well! it's not given to a gently bred lady such as myself to even speculate.

*flutters fan vigorously*

Thankfully of course it has never managed to obtain vouchers for Almack's. And I am always firmly not at home to those endless and quite vulgar cousins that seems to pop out of the woodwork every other month.

Sedna indeed!

-- Kapusniak, Stefan e

[ronebofh.livejournal.com]

The real question: how are astrologists going to work Sedna into charts?

[mmcirvin.livejournal.com]

Astrologers have already been messing around with Varuna and Ixion; some of them are very keen on that sort of thing.