After some thought, I think I'm using the following definition of planet:
An object formed in a protoplanetary disk (http://en.wikipedia.org/wiki/Protoplanetary_disk) (this excludes Oort cloud objects such as Sedna and the interstellar objects Oph 1622), not a star (as a rule of thumb, this means smaller than 14 jupiters), large enough to have had an atmosphere during formation (as a rule of thumb, this means larger than the moon), and not in the gravitational influence of another planet (I mean this to exclude not just moons but also plutinos (http://en.wikipedia.org/wiki/Plutino), though in our particular solar system plutinos are all excluded by the size restriction anyway).
Under this definition, 2003 UB13 almost qualifies, but not quite. Oph 1622 does not, because it doesn't appear to have formed in a proplyd.
There are plenty of other definitions out there, and many of those are at least more concise; the purpose of this poll was to present a bunch of corner cases and see how people's perceptions of the objects affect the validity of the various definitions out there.
I think your definition is too restrictive, and inapplicable. I doubt we can really say enough about how planets formed, to be able to use that as a definition. For example, suppose you found a rocky body out in the Kuiper belt, in an eccentric orbit? Would you propose that it had formed in the proplyd and got ejected, and so was a planet, while its neighbours were not?
I am more inclined to call just about anything whose shortest orbital period is around a star, a planet, and to accept a range of subtypes. Gas giants, rocks, snowballs, Trojans,...
The point of my definition, though, is to make determining whether an object is a planet actually useful for our understanding of the formation of the solar system, rather than merely a stamp-collecting exercise.
As to your example, if I found a rocky, Mercury-sized object in the Oort cloud (which I think is what you meant, as Kuiper belt objects are thought to have formed in the proplyd), I'd have to conclude that it wasn't a comet, just the same as if I found a brown dwarf in the Oort cloud I'd have to conclude that it wasn't a comet.
I don't mean to claim that mine is the only such definition. Maybe a definition like "any astronomical object with a metallic core surrounded by other material" would better match our current expectations.
to make determining whether an object is a planet actually useful for our understanding of the formation of the solar system My father (http://www.ociw.edu/research/sshectman/) pointed out to me that this definition will have zero effect on what science professional astronomers do. The only actual scientific effect it might have is on how much PR, and thus funding, they get, and so the best definition is the one that will get the most headlines going forward. Be too permissive and planet discoveries aren't news. Too strict and they don't happen often enough. The rounded bodies definition is probably about the right balance.
What made me suspicious is that the anti-pluto links on the site are much more authoritative than the pro-pluto material. Not to say that there isn't good material on the pro side, but a link to the primary source of the pro scientific arguments would balance the links to the antis, and that imbalance doesn't look right.
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momijizukamori
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Date: 2006-08-17 07:05 pm (UTC)Under this definition, 2003 UB13 almost qualifies, but not quite. Oph 1622 does not, because it doesn't appear to have formed in a proplyd.
There are plenty of other definitions out there, and many of those are at least more concise; the purpose of this poll was to present a bunch of corner cases and see how people's perceptions of the objects affect the validity of the various definitions out there.
no subject
Date: 2006-08-18 03:07 am (UTC)I am more inclined to call just about anything whose shortest orbital period is around a star, a planet, and to accept a range of subtypes. Gas giants, rocks, snowballs, Trojans,...
no subject
Date: 2006-08-18 02:12 pm (UTC)As to your example, if I found a rocky, Mercury-sized object in the Oort cloud (which I think is what you meant, as Kuiper belt objects are thought to have formed in the proplyd), I'd have to conclude that it wasn't a comet, just the same as if I found a brown dwarf in the Oort cloud I'd have to conclude that it wasn't a comet.
no subject
Date: 2006-08-18 03:09 pm (UTC)I don't mean to claim that mine is the only such definition. Maybe a definition like "any astronomical object with a metallic core surrounded by other material" would better match our current expectations.
no subject
Date: 2006-08-22 05:30 am (UTC)My father (http://www.ociw.edu/research/sshectman/) pointed out to me that this definition will have zero effect on what science professional astronomers do. The only actual scientific effect it might have is on how much PR, and thus funding, they get, and so the best definition is the one that will get the most headlines going forward. Be too permissive and planet discoveries aren't news. Too strict and they don't happen often enough. The rounded bodies definition is probably about the right balance.
no subject
Date: 2006-08-18 03:50 am (UTC)(of COURSE I'm joking.)
no subject
Date: 2006-08-18 05:12 am (UTC)no subject
Date: 2006-08-18 02:18 pm (UTC)no subject
Date: 2006-08-20 05:48 am (UTC)no subject
Date: 2006-08-22 05:19 am (UTC)no subject
Date: 2006-08-22 05:38 am (UTC)