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If gravity is required, what are the planets in the SolarSystem?

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Old April 21st 04, 10:55 PM
Matthew Funke
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Default If gravity is required, what are the planets in the Solar System?

"Rodney Kelp" wrote in message
I thought it had to do with orbit. If it orbits a sun, it's a

planet. If it
orbits a planet it's a moon. Large elliptical orbits by tiny

objects don't
count as planets. Comets and asteroids can't have moons because of
insufficient mass, therefore can't be planets.

What about 243 Ida's moon, Dactyl?

Is 243 Ida therefore a planet?

Another line of reasoning might be that what we call it is what it


Sure. The bodies in question don't care.

You could have a planet floating around in deep space that has

escaped it's
sun or the sun burnt out. A lost planet? A rogue moon?

Or an asteroid or a comet?

-- Best regards,
Matt Funke

Old April 23rd 04, 04:59 PM
Jeffrey Turner
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Default If gravity is required, what are the planets in the Solar System?

quilty wrote:

No body in the Solar System is round. I assume that
you'd have to go by some sort of percentage deviation
from a iso-potential surface.

Perhaps he meant "roundish"?

Just off the top of my head, we'd add: Earth's Moon,
Io, Europa, Ganymede, Callisto, Titan, Titania, Triton,
and Charon. If we take it all the way down to Ceres'
size / sphericity it'll be a mess. The big question is,
where's the dividing line and WHY?

Maybe I was just reading between the lines, but I got the impression
that he was going on the principal that planets orbit a star and moons
orbit a planet which orbits said star. That would leave out all of the
moons that you listed.

Since you seem violently against such criteria, what would you suggest
as a criteria for determining whether an object is a planet?

The Sun's gravitational pull on the Moon is greater than the Earth's.
The moon is orbiting the Sun.


A man, a plan, a cat, a canal - Panama!

Those who do not learn from history are
doomed to repeat it. --George Santayana

Unthinking respect for authority is the
greatest enemy of truth. --Albert Einstein

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left to lose. --Kris Kristofferson


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