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View Full Version : Wait, so now there's no such thing as extra-solar planets?



DaveDauria
2006-Aug-25, 12:49 AM
I mean if I understand correctly for something to be a planet one of the requirements is that it orbits around "The Sun". So since none of the actual extra solar planets orbits "The Sun" and actually orbit some other star arn't all of them, every single one, not a planet either?

Gillianren
2006-Aug-25, 12:59 AM
If you read the whole thing, you will note that it expressly states that it is intended to clear up the confusion "in the Solar System." Direct quote. So, in the Solar System, no, there's no such thing as an extrasolar planet.

DaveDauria
2006-Aug-25, 02:05 AM
If you read the whole thing, you will note that it expressly states that it is intended to clear up the confusion "in the Solar System." Direct quote. So, in the Solar System, no, there's no such thing as an extrasolar planet.



Oh, missed that part. Thanks for the info.(Though I still wonder if the new definitions for planets will be used for extra-solar planets and how that would change any of their classifications.)

CuddlySkyGazer
2006-Aug-25, 02:40 AM
Although the new IAU definition stricly only defines planets within our Solar System, it is likely that it will used by analogy to define extra-solar planets. So for an object to be an extra-solar planet, it will have to be in orbit around a star, be 'round by gravity' and to have 'cleared the neighbourhood' around its orbit. All the objects currently listed as extra-solar planets satisfy the first two criteria and almost certainly satisfy the third.

You also have to take into account the previous definition of a planet made by the IAU Working Group on Extrasolar Planets of 28 February 2001 (link) (http://www.dtm.ciw.edu/boss/definition.html):

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

This is consistent with the new IAU definition.