Fiddle About

[den]

I was wondering what the world would look like if it was a moon of a large, ringed planet...





Once every month or so the world would be eclipsed for a couple of days. It would be very dark, and I imagine rather cold, especially in the winter hemisphere.



Low orbits would be interesting.

Comments

The earth is doomed!

[(Anonymous)]

Hey bat! Bad news, but with the numbers you gave me (host planet having twenty times the radius of earth, and the orbital radius being eight times the diameter of the host planet, and assuming the host planet has a density of earth or greater [a very good assumption]), the tidal forces (from gravity being stronger at one side of the earth than the other) will rip earth apart, adding more rings to the system. This would happen pretty quickly in the lifetime of the solar system, so no chance of earth evolving life. Plus, the calculation's harder, but it's also possible that the Roche Lobe of the two planets would lead to some radius of an equipotential circle between the two, rather than just a pin point, so earth's atmosphere would drain away to the larger planet...before the earth broke up, of course.

Shame, really.


-Davros

Re: The earth is doomed!

[dewhitton.livejournal.com]

Bugger.

Thanks for the calculations, Dav. At what point would the earth be safe?

Re: The earth is doomed!

[(Anonymous)]

Basically, my simplified calculation is:

rho*Rp^2/(2*Ro) > 1 (For earth to break up)

Where rho is your density of the planet, in earth units. (taken here to be one, though it's probably greater.), Rp is the Radius of the planet in Earth radii (the number you gave me was Rp=20), and Ro is the radius of the orbit, in units of the radius of the larger planet (8, as you gave me). So, plugging those in we get roughly 25, which is much greater than one. Also, this is a rough calculation, so getting a value just below one would probably lead to global destruction, too.

I'd say take rho to be 5 (I'll look up a better number, one that's radius-dependent based on the other planets in the solar system tomorrow), then play with Rp and Ro until you get a value of .1 or less.

Also, I guess I forgot to mention "Very nice artwork, it looks quite good."

-Davros

Re: The earth is doomed!

[(Anonymous)]

Hey again, bat!

Well, I was wrong (about some things, the earth still gets destroyed, probably).

Density, in fact, goes down with increasing radius. Poor astronomy on my part when I don't have a textbook with me. However, an important point is that Jupiter is 11.2 times the radius of the Earth. Planets don't get bigger than this, even when you add more mass, as they'd just collapse further. Radius will only go up when you add enough mass for nuclear fusion to start up, which again, would be bad news for the earth, sitting 10^7 kilometers from the sun (the sun, of course, having a radius of 7*10^7). Still, if you crank the radius down to a Jupiter radius (Rp=11.2), and use Jupiter's density in Earth units (1.33/5.52 = .24), and again using 20 for Ro, you get about 2. More destruction for Earth.

So anyway, I retract what I said earlier. If you'd like the Earth to survive (always a good idea), use one quarter for rho, an Rp no larger than 12, and again aim for a value of the earlier equation less than .1 ...

Happy genesising!

-Davros