The Day the Earth Stood Still

[Dana Gold]

Hey, wait a minute! You are now saying the gas giant and rock-like object (asteroid?) are equivalent to the density and mass (respectively) of our moon (which is not a "rock-like object) and Jupiter! ....

I wanted to know exactly how big

The actual mass for either

Your calculus professore and especially Mr. Spock, would not like that assumption
According to the Roche Limit the following would definitely matter:

when I didn't care how big it really was, or how far away.

So, you could draw the planet, whatever, as big as you like; because on "artistic grounds" the whole equation wouldn't matter.....that's what's so cool about science fiction....one is not limited to the quantum/physics laws of this particular universe......nor bound by the socio-religious dogma of misleading pseudo-normalcies from the self-appointed "dominionists" called Homo Sapiens.

Dana

[Priestess]

The idea was to figure out how large it could be drawn without ignoring reality. You said it yourself, the picture you linked had a planet/moon that appeared too large in the sky to be physically possible. So there must be an limit of how large it can be drawn and still remain possible. I didn't say to use the mass of the moon, only the density. The same with using the density of a jupiter, not necessarily it's mass. Nevermind ...

[Dana Gold]

Sorry, Melissa; I didn't mean to cause you any frustration

Dana

[Meresa]

Originally Posted by Dana Gold

You've not given the mass and density of the objects (gas giant and rock-like object) of either scenario; therefore it cannot be determined...http://en.wikipedia.org/wiki/Roche_limit

Unless you would perhaps know of a solution, in which case, please enlighten me.

Dana

I have imagined two extreme situations involving tidal forces.

One:
A planet orbiting a gas giant just outside its Roche Limit, (but far enough out to keep its atmosphere from spilling out of the LaGrange points). It was further away when it formed, so it is a bit rounder than tidal forces allow in its current orbit. So the tides stretch the atmosphere more than the planet, such that the planets atmosphere and oceans are split in two. There is air and an ocean on both the near and farside end, with a band of vaccuum around the "waist". Between the oceans and the vaccuum are regions analogous to various elevations on earth. Near the vaccum there will be permafrost and glaciers. Near the oceans there will be tropical marshes, savannas, and maybe even a desert or two. Midway there will be climate similar to the forests in the foothills of mountain ranges. From space, the planet will resemble a giant easter egg. What is interesting is that there are two separate bioszones, each with potential for wildly divergent evolution. With a little luck, the system might remain stable for hundreds of million years before the tides shift the planet out of its current orbit.

(for a similar but inverse situation, read about the planet Jinx in Larry Niven's Known Space.)

Two:
A terrestrial planet with a large rocky moon in close orbit. The moon raises tides so large that the main ocean is mobile, moving around the planet every few days. Above a certain latitude there will be normal dry land, but in the "ocean" zone there will be an enteresting ecology. Not unlike tidepools, but much more extreme.

If the moon's orbit is longer than the day, then tidal friction will push the moon outward and the tides will weaken with time.

It the moon's orbit is shorter then the day, then it will spiral inward towards its Roche limit until it breaks up and forms a pretty ring like Saturn's. Of course prior to this, volcanism and earthquakes will increase along with the tidal ocean movement to likely make the primary planet uninhabitable....

If humans can imagine such worlds, I am sure that nature will come up with even more interesting ones....

[Meresa]

Originally Posted by Priestess

The question mattered to me on artistic grounds, I wanted to know exactly how big I could draw something in the sky without it being impossible, when I didn't care how big it really was, or how far away.

If two bodies are tidally locked and dense enough they could be quite close so I wouldn't worry about it too much if I were you.

For more info see Robert Forward's Flight of the Dragonfly.

[Dana Gold]

Yes! , an oblong planet ; thanks, Meresa. I hadn't thought of that ; got stuck in the mode of thinking of the "normal" planet . What would be intriguing is that the spin of this hypothetical planet would be so great that a day might be only a few hours.......daylight savings would be s/w useless, there....

Thanks again

[Priestess]

Originally Posted by Dana Gold

Sorry, Melissa; I didn't mean to cause you any frustration

Dana

That's alright. Not too very frustrated. But your alien avatar has inspired me, I just needed to find an image that reflects my general physical health and state of emotional well-being.

[short311fan]

beginning to think i'm way outta my league on this thread, gonna go back to playing cheesy horror-movie and spagheti-western music on my guitar! lol