The Sun's 10th Planet... Sedna?

dsanfte writes "While NASA remains intentionally vague, promising only a news conference Monday, The Australian has the details. The new planet, dubbed Sedna after the Inuit goddess of the sea, is 3 billion km further from the sun than Pluto, and is slightly smaller at 2000km in diameter. This discovery has apparently reignited the debate as to how big a solar object must be in order to qualify as a 'planet', but it is significant nonetheless."

Comments

for comparison purposes:

[Anonymous Coward]

Pluto is 2300 km diameter, ranges from 4.3 to 7.4 billion km from the sun.

http://www.windows.ucar.edu/tour/link=/pluto/stati stics.html

Re:Back to grade school for retraining...

[thomasdelbert]

Correction - Neptune was farther from Pluto from January 21, 1979 to Feb. 11, 1999 but at this time Pluto is farther from the sun than Neptune.

Of course, there's debate as to whether Pluto-Charon is a planet with a moon, or a double planet...

- Thomas;

Re:It's a Kuiper object...

[Gutboy_Barrelhouse]

No. Charon is slightly smaller than Quaoar.

Sedna is over 4 times the size (volume) of Quaoar.

Whether it's a planet is a silly argument, but even so, "we already have Quaoar" is really irrelevant.

Inuit Contributions

[Vagary]

Hockey was invented somewhere in Europe or European North America in the 19th century. Lacrosse was invented by Indians near the St. Lawrence and is played on grass rather than snow, so I doubt the Inuit were involved.

Inuit inventions include snowshoes, toboggans, dogsleds, kayaks, toggle harpoons, and various other tools for hunting and travelling in the North as well as snow and ice civil engineering techniques. Pretty impressive, I'd say, for a culture with almost no wood, rock, or metal. They've probably contributed as much as any other non-Eurasian colonialised culture, and they make some really cool art.

Re:A lot of astronomers don't want to count Pluto

[r2vf]

IMO, Pluto should [shouldn't?] be labeled an asteroid since it's smaller than even our own moon [wikipedia.org].

An interesting point, though to be fair, its an arbitrary cutoff. There are moons elswhere in our solar system larger than Mercury, which is indisputably a planet, for example. Also its worth pointing out that our moon is large enough that it and Earth are sometimes called a double planet. Consider this, Luna does not orbit Earth as near the equator as is usual among most other moons. Also, peculiar to all 138 known moons with the exception of Charon, it possesses an orbit where the effect of the Sun's gravity is greater than that of Earth's. Without their host planets, they would float off, wheareas the moon would continue orbiting the sun quite contently.

Re:It's a Kuiper object...

[RobertFisher]

The question becomes even more convolved once we move outside the solar system, since we now know of a wide diversity of systems, of which our own solar system is only one particular instance. (And perhaps not even typical at that.) We know that there are objects extending all the way down from massive stars (around 100 Msun) to hydrogen-burning stars like our sun to brown dwarfs to planets. Clearly any definition of a planet must apply not only to our solar system, but also to these extrasolar systems. Some of these systems are much like our own (for instance, they may contain a brown dwarf orbiting a star, or a planet orbiting a star), and some (including a few systems of low enough mass to qualify as a planet) are "free-floaters" -- just sitting out there by themselves in space.

I think ultimately the question is whether there is a single continuous "initial mass function" of isolated objects or not. The best idea as to how stars acquire their initial mass is that turbulence in the interstellar medium, which exists on all scales, establishes a power-law distribution of initial masses. Every once in a while, you get a very strong shock which passes by inside a giant molecular cloud and forces the collapse of a large region which then goes on to form a massive star. But more typically, you form stars more like our sun. And just as rare as massive collapses are very small mass ones which go on to form isolated brown dwarfs and free-floating planets. If this model holds up to be true, then we are all mincing words in our definitions of isolated systems, since they are all manifestations of the same universal formation process.

However, to avoid the difficult question of formation mechanisms, an IAU working group of some of the most respected people in the field established a working definition to define by fiat what it means to be a brown dwarf, and a planet. Extrasolar "planets" are those objects orbiting a star which are beneath the deteurium-burning limit -- regardless of how they are formed. "Brown dwarfs" are defined to be those which burn deuterium but not lithium, and "sub-brown dwarfs" (NOT free-floating planets!) are defined to be those isolated objects which do not burn deuterium. Even the working group itself admitted that this definition was not satisfying to a single member of the group, and so it is likely it will be replaced at a later time with something more physically-motivated. The "planet/planetismal/KBO" distinction was pushed back to our own solar system, since it will be some time before anyone sees anything that small in another system.

Also of interest is the following link, which gives a history of previous claims for additional planetary members of our solar system : SEDS.