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View Full Version : Sad About Pluto? How about 110 Planets in the Solar System Instead?



Fraser
2017-Feb-21, 08:10 PM
A new geophysical definition has been proposed by a team of planetary scientists, one which would result in a Solar System of 110 planets.
The post Sad About Pluto? How about 110 Planets in the Solar System Instead? (http://www.universetoday.com/133525/sad-pluto-110-planets-solar-system-instead/) appeared first on Universe Today (http://www.universetoday.com).


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Amber Robot
2017-Feb-21, 10:24 PM
How much self-gravitation is "sufficient"? How round is round?

If Ceres becomes a planet is it also an asteroid?

And, by the way, this artist's conception is pretty bad:
22112

swampyankee
2017-Feb-22, 02:42 AM
The number of items in a category should not, a priori, invalidate it. We haven't redefined "element" because there are too many of them.

Roger E. Moore
2017-Feb-22, 02:54 AM
I added something about this to the end of a thread on Pluto becoming a planet again.

https://forum.cosmoquest.org/showthread.php?153664-Is-Pluto-about-to-be-reinstated-as-a-planet&p=2393007#post2393007

Is there anything new in this, or is this just some of the older arguments being re-run through the media mill with a little push?

Has anything really new come out to justify a re-re-re-definition of "planet"?

DonM435
2017-Feb-22, 06:08 PM
The number of items in a category should not, a priori, invalidate it. We haven't redefined "element" because there are too many of them.

Ceres, Pallas, Juno and Vesta were accepted as planets, until more and more little ones turned up, at which point the nomenclature was overhauled.

swampyankee
2017-Feb-22, 06:46 PM
Ceres, Pallas, Juno and Vesta were accepted as planets, until more and more little ones turned up, at which point the nomenclature was overhauled.

They were reclassified because there were an order of magnitude smaller than the other planets.

DonM435
2017-Feb-22, 06:50 PM
They were reclassified because there were an order of magnitude smaller than the other planets.

True, and that was a convenient excuse. However, had there been no more small planets discovered in the asteroid belt, I'd suspect that they'd have remained on the "list" of planets.

Hornblower
2017-Feb-22, 08:03 PM
One popular argument for limiting the number of objects we call planets to somewhere around 8 or 9 was that otherwise our children would have to memorize too many of them. If we the people of the general public are foolish enough to make outrageous demands on our children, that's our problem, not the astronomers' problem. By that goofy line of thought, we the people of the USA should have limited the number of states to the original 13. Maybe we the people of Planet Earth should have done something to prevent the breakups of the USSR and Yugoslavia.

swampyankee
2017-Feb-22, 09:12 PM
True, and that was a convenient excuse. However, had there been no more small planets discovered in the asteroid belt, I'd suspect that they'd have remained on the "list" of planets.

A basic point is they were reclassified because of what they were, not a combination of what they were and their location.

In any case, the IAU would have avoided a lot of ridicule had they just done this:

Celestial Objects
2 Single objects
2.1 self-luminous
2.2 not self-luminous
2.2.1 Planets (orbit self-luminous objects)
2.2.1.1 Gas planets
2.2.1.2. Ice planets
2.2.1.2 terrestrial planets
2.2.1.3 dwarf planets
2.2.2 Satellites (orbit planets)
2.2.3 ....


Hierarchical categories are a good thing.

II: Not self-luminous
a) Planets