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Tom Mazanec
2016-Jun-16, 05:10 PM
Now that we may have Planets Ten through Twelve, suppose Planet Nine is 10 Earth masses, planets Ten, Eleven and Twelve are 2-4 Earth masses, and the inner Hills Cloud has a dozen objects between Mars and Venus in mass and scores as big as Titan or Ganymede (is this observationally plausible).
Would this make Planet Nine, not clearing its orbit, a dwarf planet an order of magnitude bigger than Earth?

antoniseb
2016-Jun-16, 05:21 PM
Now that we may have Planets Ten through Twelve, suppose Planet Nine is 10 Earth masses, planets Ten, Eleven and Twelve are 2-4 Earth masses, and the inner Hills Cloud has a dozen objects between Mars and Venus in mass and scores as big as Titan or Ganymede (is this observationally plausible).
Would this make Planet Nine, not clearing its orbit, a dwarf planet an order of magnitude bigger than Earth?

IF the hypothetical planet 9 is several Earth masses, AND has not cleared its orbit, then by the current definition it wouldn't be a planet, but that wouldn't make it a dwarf. It would probably need some new designation, since the current definition doesn't cover such a situation.

George
2016-Jun-16, 05:52 PM
IF the hypothetical planet 9 is several Earth masses, AND has not cleared its orbit, then by the current definition it wouldn't be a planet, but that wouldn't make it a dwarf. It would probably need some new designation, since the current definition doesn't cover such a situation. Why not a dwarf planet?

At the 600AU (rough distance estimate) a planet would need to be, IIRC, about 1.6 Earth masses to clear its orbit.

01101001
2016-Jun-16, 07:10 PM
Nine alone: Planet.

Wikipedia: Planet Nine (https://en.wikipedia.org/wiki/Planet_Nine)


Brown thinks that no matter where it is speculated to be, if Planet Nine exists, then its mass is higher than what is required to clear its feeding zone in 4.6 billion years, and thus that it dominates the outer edge of the Solar System, which is sufficient to make it a planet by current definitions. Using a metric based on work by Jean-Luc Margot, Brown calculated that only at the smallest size and farthest distance was it on the border of being called a dwarf planet. Margot himself says that Planet Nine satisfies the quantitative criterion for orbit-clearing developed by him in 2015, and that according to that criterion, Planet Nine will qualify as a planet—if and when it is detected.

Lots of assumptions, of course. Lots.

But fewer assumptions than it takes to talk about Planets Ten through Twelve. Don't make up too many imaginary friends.

George
2016-Jun-16, 08:37 PM
For planetary status, the Jean-Luc Margot method yields a 1.6 Earth mass for 600 AU, 2.5 Earth mass for 900 AU -- though this is my math. Was their "smallest" mass estimate close to this?

For the Ann Marie Madigan hypothesis -- the minor planets masses combine, primarily due to their slowness at aphelion, to cause what is the observational evidence suggesting the more popular Planet 9 hypothesis -- the inner most minor planet (~ 100AU) would have to have a mass of only about 1/4 that of Earth (100x more massive than Pluto), to be a "planet", not to mention eccentricity issues when applied to clearing, assuming that would add some headache to it.

It is interesting just how much more massive objects must become to clear their orbital zone as distance increases. This is, I think, due to their reduced orbital speed not being able to throw things as effectively.

DaveC426913
2016-Jun-16, 10:52 PM
A large planet that has not been able to clear its orbit of other bodies?

I'm thinkin' you're right it does need a new designation. I'm thinkin' it would be called a rogue intruder... or a recently captured planet.
;)

Noclevername
2016-Jun-17, 12:54 AM
Doesn't "clearing its orbit" depend very much on how many other bodies it shared its orbit with to begin with?

Solfe
2016-Jun-17, 01:12 AM
Do you think there was some segment of the population before 1930 that got rankled by the fact that people said "Planet X" when they really meant "Planet IX"? :)

I can hear the typewriters clattering:

"Dear Sirs, I wish to correspond with you about your piece entitled, 'SEE ANOTHER WORLD IN THE SKY.'"*

(*no they actually don't say "planet X" in that piece, but it would be funny...)

publiusr
2017-Mar-31, 07:33 PM
Looks like we have four candidates now
http://www.universetoday.com/134824/four-candidates-planet-9-located/

Oviraptor
2017-Apr-12, 08:53 AM
I would think a planetary mass object, if it did not clear its orbit would either be very new, and or is being bombarded by any objects in its orbit. We should be be able see that, if it was happening.

George
2017-Apr-12, 01:54 PM
I would think a planetary mass object, if it did not clear its orbit would either be very new, and or is being bombarded by any objects in its orbit. We should be be able see that, if it was happening. If it is, as they predict, > 1.6 Earth mass at ~ 600 AU then you would be right. But it does take a lot of orbits to dominate its orbital real estate.

publiusr
2017-Apr-29, 08:00 PM
And what is the time table for clearing an orbit. There are lots of Trojans to rid.

George
2017-May-01, 09:02 PM
And what is the time table for clearing an orbit. There are lots of Trojans to rid.
One suggestion is to use the main sequence period for any given star, but perhaps one billion years could serve even better.

Hornblower
2017-May-01, 09:57 PM
Let's not forget that the IAU resolution was framed for the present-day state of our solar system, and that no attempt was made to generalize it for other systems.