The search for Planet 9 ...join in

Argumemnon said:
What do you mean? That's part of the definition.
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Yes, but it's a fuzzy definition. How much deviation from hydrostatic equilibrium is acceptable? There are going to be bumps, craters, hills, etc on any dwarf planet. At what point is a mountain no longer just a bump on a spheroid, but a deviation large enough to disqualify it? We haven't really had to deal with edge cases yet, and we might never have to in our solar system, but the definition doesn't actually provide a sharp dividing line.
 
Beerina said:
I'm a fan of the big enough to be a ball definition (mentioned above.) Don't care if it is in orbit about something besides the sun, nor if there is other smaller non-ball junk in its orbit.
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I'm not a fan of the cleared orbit aspect. That would make Jupiter not a planet during the early stages of solar system evolution, which is pretty absurd. But it should orbit the sun, not another planet. Titan is a moon, not a planet. The Moon is a moon, not a planet.
 
Ziggurat said:
Yes, but it's a fuzzy definition. How much deviation from hydrostatic equilibrium is acceptable? There are going to be bumps, craters, hills, etc on any dwarf planet. At what point is a mountain no longer just a bump on a spheroid, but a deviation large enough to disqualify it? We haven't really had to deal with edge cases yet, and we might never have to in our solar system, but the definition doesn't actually provide a sharp dividing line.
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What he said :)
 
Ziggurat said:
I'm not a fan of the cleared orbit aspect. That would make Jupiter not a planet during the early stages of solar system evolution, which is pretty absurd. But it should orbit the sun, not another planet. Titan is a moon, not a planet. The Moon is a moon, not a planet.
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I think it's a protoplanet at that point.

Which, I think may be a definition that can only be applied retrospectively after the potential protoplanet has met or failed to meet the definition of planet?
 
Ziggurat said:
Yes, but it's a fuzzy definition. How much deviation from hydrostatic equilibrium is acceptable? There are going to be bumps, craters, hills, etc on any dwarf planet. At what point is a mountain no longer just a bump on a spheroid, but a deviation large enough to disqualify it? We haven't really had to deal with edge cases yet, and we might never have to in our solar system, but the definition doesn't actually provide a sharp dividing line.
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And it's going to change depending on the environment. KBOs made primarily of ice are going to round themselves out with much less mass than a rocky planetoid could. Contrariwise, KBOs can get much bigger without clearing their orbit because there's so much more orbit to clear.
 
macdoc said:
For those down under

[qimg]http://cdn.newsapi.com.au/image/v1/256f9662d3e61f6cb975d4a151c75f88?width=650[/qimg]



http://www.theaustralian.com.au/hig...n/news-story/37811e566e0bd685ae427dbd36bf9ead

Lots of cool hands on science with an interactive aspect that drew a million fresh crowd sourced analysis

Join in the hunt

https://www.zooniverse.org/projects/skymap/planet-9
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Great Zooniverse project, I found I have to do it on as large a display as possible, no iPhone
:D
 
Ziggurat said:
Yes, but it's a fuzzy definition. How much deviation from hydrostatic equilibrium is acceptable? There are going to be bumps, craters, hills, etc on any dwarf planet. At what point is a mountain no longer just a bump on a spheroid, but a deviation large enough to disqualify it? We haven't really had to deal with edge cases yet, and we might never have to in our solar system, but the definition doesn't actually provide a sharp dividing line.
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Yeah, Mimas is the smallest of the lot and it's still pretty damn round.
 
Ziggurat said:
I'm not a fan of the cleared orbit aspect. That would make Jupiter not a planet during the early stages of solar system evolution, which is pretty absurd. But it should orbit the sun, not another planet. Titan is a moon, not a planet. The Moon is a moon, not a planet.
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I guess you could use the presence of a common barycenter within another body to distinguish the two.
 
carlvs said:
Actually it was the tenth planet - everyone forgets about Ceres...:)



Interestingly, some planetary scientists would agree with you on this...
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Argumemnon said:
Though Ceres wasn't considered a planet when Pluto was discovered.
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Hmm, comparing the sizes of Pluto and Ceres, Pluto is over 10 times more massive. Ceres is actually smaller than Pluto's moon, Charon too. Then again, Pluto itself is smaller than our own moon, and only about a fifth as massive.
 
It's as bad as most crappy human criteria. We should keep it as we have always done, it's a planet if we say it is.
 
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Just a note to say that there are two Zooniverse-based projects looking for a 9th planet, Planet 9 and Backyard Worlds: Planet 9.

The former is what the OP references, and is based on data from SkyMapper; the latter is a bit older, and is based on data from WISE. The two projects certainly overlap - at least in terms of the explicit goals of finding a 9th planet - but are also very complementary. For example, Planet 9 will likely find some previously unknown asteroids and perhaps TNOs (trans-neptunian objects) - as will Backyard Worlds (but likely with little overlap) - while Backyard Worlds will certainly find previously unknown brown dwarf stars with large proper motion (meaning they are very close to us).

Both projects had manic levels of participation in the beginning - their fora ("Talk") have lots of pretty insane comments, for example - but as enthusiasm has waned, the work of the patient, careful volunteers continues. It's pretty amazing what amount of real science can get done with just "clicks"! :)
 
I always liked Stephan COlberts definition of a Planet:

Would Galactus eat it for Lunch?
 
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