Paging astronomers

[ffutures]

For a plot point in a possible future Supergirl story I've been wondering about Krypton's moons. This page puts together information in the Superman comics etc. and makes some guesses about the moons as described there:

http://www.bigapricot.org/other/krypton.shtml

My feeling on this is that they're too close to the planet and to each other, and would either drift into tidal lock or end up catapulting each other out of orbit pretty quickly. I know that there are at least a couple of astronomers on my friends list, anyone able to crunch the numbers?

Comments

[dsample.livejournal.com]

OK. If we assume that all four original moons fell in orbits that obeyed Bode's Law, and the two inner moons are the ones that have gone missing/been destroyed, the two left would have a nice 1:2 ratio, and be Bode's Law compliant.

[dandello.livejournal.com]

These were my figures and I freely admit my math occasionally sucks big time.

The masses were SUPPOSED to be figured with the Earth's Moon as 1.

However, if somebody wants to give me figures that would work better, I have no problem with that either.

I had actually figured the two destroyed moons to be very very small and fast.

[ffutures.livejournal.com]

Small and close in works well for that, but they'd barely be visible except as faint moving dots - that silly picture really doesn't work!

[ffutures.livejournal.com]

And PLEASE don't get me started on the "science" of Another Earth, at least the bits we see in the trailer, or The Return of the Time Lords...

[dandello.livejournal.com]

Wouldn't dare. I only allow a limited number of physics violations per universe - and the size of habitable planets isn't one of them - today.

But if we assume that the pic is (maybe) Kryptonian landscape art rather than a photo-depiction, and knowing that Earth artists invariably exaggerate the size of the Moon by massive amounts - then there's no reason not to do something like estimate the difference in arc between the two moons and work some figures from that.

Just eyeballing it it looks like one is about 5 times wider (in arc) than the other. Since it's probably not reasonable for one to be 5 times further away from the planet, then one is much smaller - but it doesn't necessarily have to be the closer one that's smaller.

[dandello.livejournal.com]

I worked through these trying to get the visible arcs to make some sense:

	M(M)	diameter(km)	mass (kg)	distance (km)	orbital period (days)	Arc in min.
Koron	0.502	2840.55	3.69E+22	345869.1	21.33	27.43
Mithen	0.017	915.97	1.24E+21	538018.6	41.38	5.69

This makes the two moons very different in size and gives visible arcs in line with the picture (although much smaller than shown but I figure the artist exaggerated - a lot.)

I hope this works better.

[ffutures.livejournal.com]

That feels a lot more reasonable - many thanks for going to so much trouble.

I really hate to say how minor the plot point will be, if it happens at all; just Kara missing something because she's not very familiar with tidal cycles - especially since she's from an essentially artificial environment.

[dandello.livejournal.com]

This is the first time anybody's even commented on the moons - and the figures certainly aren't carved in stone so if somebody wants to let me know how to make it work even better, I don't mind at all.