Meleti and Maci - Whistler's Worldbuilding

Actually, such a cometary tail would be extremely bright coming off of a super-Plutonian world in the Habitable Zone. So instead of being something like an Eye, it would be more like a Tail.

The problem I see is that Meleti is apparently not an ice planet. Why is this body when it's at the same distance from Letuaf as Meleti?

Incidentally, red dwarfs are brighter at the very beginning (first billion years or so, less for larger stars) of their lifespan than during the regular main sequence.

Like the previously-proposed impactor, Maci originally came from the Kuiper Belt and was perturbed out, swinging by other planets before settling in around Meleti. For a moment, it may have destabilized the orbital resonances, but gravitational interactions pulled them back into lockstep.

Edited by TheWhistleTropes on Aug 23rd 2020 at 4:43:18 AM

OK; I still think you may want to check whether Meleti is too far away from or too close to Letuaf for habitability, though. Going back to some OP questions, note that tidal locking is not necessarily mutual - Maci may be locked to Meleti but not necessarily the other way around and thus could be visible from everywhere on Meleti's surface. Also, I wonder what the topography of Meleti looks like - a globe-spanning ocean with isolated islands and atolls á la Hawaii?

Also, another thing that came to mind, ozone layers are not entirely radiation-tight. If Letuaf emits enough UV radiation to form a much thicker ozone layer than Earth, lifeforms will have to deal with the extra radiation load. Which for example means that humans evolving on Meleti will all be dark skinned.

Admittedly, the sapient lifeform is dragons (my movie is a furry movie). Since the flora would be black, I would think the fauna would too.

And yes, it is mostly ocean with some Hawaiian chains. The chain where the story takes place one in question is nearly equatorial.

Huh. Anti-UV pigments come in various colours, and I'd imagine that the eventual colour of biota would be a matter of chance (which anti-UV molecule happens to develop through evolution).

Update on Letwaf:

Putting the planets in resonance seriously destabilizes Meleti's orbit—at least, makes its variations more pronounced. Therefore, I have rearranged it to put everything in only near-resonances.

I also added two outer planets—Lamebi, a 2.14-Mearth planet out past Elfanu, and Shamong, the only planet in the system less massive than Meleti. Elfanu is now a mini-Neptune (7 Mearth) with two big moons—Jansen and Bili. Shamong is just shy of an AU out from Letuaf—a bit closer than the frost line.

Well, I can't speak of the stability of such a system as the 11-body problem is too complicated. I still think it'd be a very marginal system for any moon.

Over timescales of at least tens of thousands of years, all three of the system's large moons so far seem stable. Maci only variates in its orbit around Meleti with Saros cycles, and Jansen and Bili don't tug on each other too much.

Although really, Maci's orbit does vary in eccentricity by between 0.1 and 0.26 due to influences from Letuaf, with an average eccentricity of about 0.2. So while the system seems to be stable for the time being, it varies a lot more than your average Sarosian orbit. Nonetheless, its variations are perfectly predictable.

Edited by TheWhistleTropes on Sep 22nd 2020 at 3:10:12 PM

Actually, I think it might be better to just leave Meleti be alone. Maci's orbit is probably not stable over astronomical timescales. Perhaps my event that brings my characters back home could be something even rarer, such as a simultaneous triple transit of Famalne, Cescete, and Santal.

A solar eclipse would still be more visually striking, however.

Actually, new thoughts.

How long would it take for a semi-small moon to cause a planet to rotate? I was thinking Meleti is currently an eyeball planet, but Maci—which would now be closer to Meleti so it is stabler—orbits the planet on a retrograde orbit every ~3 days. It would still be an icy, giant comet moon, because that is simply visually striking, and perhaps its arrival is how my culture marks time due to the lack of a day-night cycle (currently).

This could probably be handwaved as some sort of recent addition to the system—possibly less than a thousand years in orbit if need be.

semi-small moon to cause a planet to rotate? A very long time? A small moon isn't going to exercise enough gravity pull to overcome that of its host star.

I would estimate that the moon were about the size and mass of Iapetus (Saturn's moon), and that it were close enough to totally eclipse the Sun occasionally.

EDIT: Yeah, those were actually its stats to begin with, except that it's twice as big.

Edited by TheWhistleTropes on Sep 30th 2020 at 12:43:44 PM

Over thousands of years, Retrograde Maci actually seems to be more stable than Prograde. It would also seem to create something more visually striking, as the rising of this close-in moon heralds a need for hurry.

Yep, looks like the retrograde is here to stay.

Edited by TheWhistleTropes on Sep 30th 2020 at 4:56:08 AM

Considering that Meleti is now an eyeball world, and that its moon regularly eclipses the sun, how would species' circadian rhythms be affected?

Depends on the period and albedo of the moon, I'd imagine, since too long a cycle means that it won't facilitate the development of a circadian (or selenal, as here) cycle. Note that there are physical limits as to how long and short it can be - too long and the moon will be stripped from Meleti, too short and the moon will fall into Meleti's Roche lobe.

I was thinking a cycle approximate to 96 hours, considering that that's the time it takes Maci to orbit Meleti.

Big bump.

So I've been tweaking some of the stats of other planets in the system, and Meleti seems to have been stretched onto an almost Mercurian elliptical orbit. I ran the numbers with my other stats and it seems to have 12-degree winters and 90-degree summers. It would also likely be in a 2:3 spin-orbit resonance as well, giving it a day-night cycle with bitter cold winters.

Buuuuut the orbit then slowly dampens after a while into a near-circular orbit.

How long is "a while"? Theoretically, no three body moon-planet-star system is stable but the timespan until decay can easily exceed the age of the universe.

As for the climate of an eccentric planet around a dwarf star - there is a paper here that discusses this. Also, one important question - what is the colour of Letuaf? Ice albedo feedbacks and greenhouse gas effects both decline the redder the host star, as greenhouse gases increasingly reflect and ice increasingly absorbs red light.

Letuaf is sort of a golden color—its spectral type is about M1.5. Hence why Meleti's skies are white instead of blue, and its flora black instead of green.

Meleti-Maci ends up stabilizing into a less eccentric orbit after about 10—20,000 years of being pulled into its eccentric orbit. So while it may for a while have a 2:3 or 1:2 spin-orbit resonance, it will most likely be pulled back into a simple tidal lock. While there is some ice around the edge of the eyeball, and a semi-large desert covering the middle third of the planet's star-facing side, about 60% of the surface on the star-facing side is water.

I would think that maybe there is some sort of mythology based on these sorts of things; once it gets more eccentric, its spin-orbit resonance could be seen as Maci or other planets winning the battle. The current generation is in a more circular stage of the orbit, but future generations may have a very long day-night cycle to cope with.