Hot Jupiters

[Crucis]

For those who haven't heard the term "Hot Jupiters" before, Hot Jupiters (HJ) are gas giants that exist much closer to their star, within the star's rocky zone.

http://en.wikipedia.org/wiki/Hot_Jupiter

The Wikipedia article states that HJ's orbit their stars at about 0.05 AU (about 0.4 LM) or less. However, the chart of discovered exoplanets on that wiki page ( http://en.wikipedia.org/wiki/File:Extrasolar_Planets_2004-08-31.png ) shows that there are a considerable number of gas giant sized planets that have been discovered at distances greater than 0.05 AU that, for Sol (a G2 Yellow star) would still be within its Rocky Zone. Unfortunately, the chart doesn't indicate the star types associated with these discovered exoplanets, so a gas giant discovered at 1 AU, might be within the gas zone, if its star was actually a M8 star instead of a G2 like Sol.


In regards to Starfire, I'm not really sure how much actual game value HJ's would add beyond flavor and accuracy. At 0.05 AU (call it 1 LM for game purposes), even an HJ's hill sphere wouldn't be all that large, and any moons that did exist would certainly be Type mH hot moons ... or worse (i.e. molten bodies that might not be colonizable at all).

Of course, if HJ's were to exist further out within the Rocky Zone ( "warm" Jupiters? ), there'd be every possibility that they could reside within the star's Biosphere... and then an Endor-like habitable "moon" would become a serious possibility. (Of course, there's also the question of how common would be a "moon" that's sufficiently large to retain a life-supporting atmosphere?)

Just thought that I'd raise this possibility, as Hot Jupiters are apparently entirely real, and thus could be justified quite easily enough.

[krenshala]

My preference is for planet mass (or size if you prefer ) is a single roll, as i've mentioned elsewhere. This means the type of planet will be determined by its size and its distance from the primary. If the giant planet is far from the primary, it is an ice giant (unless in a powerful nebula); if its close to the star, its a hot-jupiter type; if its in between it becomes a 'normal' Jovian world.

As for Giants in the hab-zone, I think it should have to be a "large" moon result (the 7+<moons>% chance) before it has a chance to be a habitable moon, whether or not it is tidelocked (the 1+<moons>% chance). This gives you an 8 to 12% chance for the innermost moon to be habitable without taking into account the orbital distance of the Giant.

Whether it should be habitable automatically or not has a few pros and cons (radiation/thermal/magnetospheric output of the Giant, etc) in addition to the normal issues dealing with distance from the primary. I haven't had the time to sit down and really figure out what my preference is on how those variables should be handled (e.g., which to 'ignore', which to simplify, and which can stay relatively more complex).

Your comments, Fred, in another thread (or three) about planet and moon formation also play into the type of moons around a gas giant. We know from Jupiter that the radiation and heat it puts off can heat the inner moons, while the outer ones are colder due to the distance from Sol. If we wanted more complicated we could figure out the "planetary formation zone" distances for various sized gas giants and apply them to the moons as modifiers for the types normally generated based on the planets distance from the star (e.g., the moons would be frozen because they are 300 LM from the primary, but its a BIG gas giant, so the inner moons are at least Barren, if not Hot, due to the thermal and radiative output of the planet, while the outer moons are still frozen).

[Crucis]

Yeah, I read where the radiation received on the surface of Io was more than enough to kill a human being instantly.

As far as Cosmic, I'm just not interested in a sysgen system that's so complex that it's unplayable. I prefer trying to sublimate as much of the realism details into less complex abstractions. For example, Hill Spheres. Hill spheres are simply too much to ask players to deal with. However, what can be done is for the designer (me, in this case) to use Hill Sphere data to help produce a set of reasonably simple and playable die roll mods for the number of moons table, and otherwise just ignore Hill Spheres at the player level.

In more detailed terms, I am ignoring actual planet types for the # of Moons modifiers within the rocky zone and am concentrating on only whether you're within the star's tidelock zone and the planet's general mass. So, in my current iteration of the # of Moons process, if the planet is a Mass 1 planet and is within the TLZ (most likely a Type H planet), it would have a -5 mod for being a Mass 1 planet and a -2 mod for being in the TLZ, for a total mod of -7 against a d10 die roll. And on the current table, this leaves a mere 10% chance of being having a single moon, which increases to only 30% if the mass 1 planet is outside of the TLZ. I decided to use TLZ instead of being sunward of the Biosphere because TLZ distances are actually more constant than the inner Biosphere boundary, and produced the results I like better.

As far as moons of gas giants and radiation, I'd probably just ignore the issue entirely, though one way to deal with it abstractly would be to make the first moon orbit distance for a gas giant 1d10 PLUS 5 tH, stating that any moons that might exist within the first 5 tac hexes are totally uninhabitable due to extreme radiation. And any moon that might exist at a 1 tH orbit was quite likely turned into a ring system, since the moon would quite likely be within the planet's Roche Limit.

If you wanted to get really, really detailed along these "radiational" lines, you should probably also state being within about 5 tH of any gas giant without active Shields causes instant death to the crew of the ship (unless the ship is crewed by a Jovian race), similar to the effect of a Neutron Star in Ultra. Oh! Come to think of it, those potential moons between 2-5 tH of a Gas Giant should probably be habitable by Jovian races, since one would seem to need to assume that if they can LIVE on such a radiation producing world, then living on a close radiation-swamped moon shouldn't pose any danger from that same radiation.


Frankly, this is just too much detail for my taste. As much as I enjoy thinking about sysgen related stuff, there's only so much detail that I think the average player can take. And worrying about radiation issues on close gas giant moons is just plainly over the top ... (hence the suggestion for a first orbit of 1d10+5 tH to abstractly "solve" the issue).

[Crucis]

As for Giants in the hab-zone, I think it should have to be a "large" moon result (the 7+<moons>% chance) before it has a chance to be a habitable moon, whether or not it is tidelocked (the 1+<moons>% chance). This gives you an 8 to 12% chance for the innermost moon to be habitable without taking into account the orbital distance of the Giant.

I forgot to reply to this part in my first reply...

The entire 7+% and 1+% stuff from Ultra (and their parallels in ISF) are a crock of manure. When you do some research and calculations using the sizes and masses of the moons in our own solar system, you eventually discover a number of interesting facts about moons and rocky planets.


A. ALL moons of 500 km and above are tidelocked to their planet. The largest moon to not be TL'd to its planet has a radius of only 210 km.

B. All "major" (i.e. 500+ km) moons in the solar system will mutually tidelock (MTL) automatically at 1 tH, even the smallest 500 km moon. And even at 5 tac hexes, 33% of major moons will MTL. (Note that this percentage includes the 3 largest moons which might be considered size 3 "large moons".) And over that 1-5 tH range, the wighted average MTL chance of all 15 major moons is 55%.

Alternatively, if you remove the 3 largest moons which would be "large moons", the weighted average drops to only about 40%. (And the 3 "large" moons will automatically MTL in the first lunar orbit of any rocky planet.)

C. Of the 15 major moons in the Solar System, 20% of them (3 of 15; Ganymede, Titan, and Callisto) are "large" moons. Of course, all of these orbit Type G planets.


Clearly, the chance for MTL is far, FAR too low. Also clearly, the chance of having a "large moon", specifically around a Gas (or perhaps Ice) Giant planet is rather too low.

I won't argue that a 1% chance for a Twin planet for a T/ST planet is too low (or not), as A) we have no real comparison and B) I don't think for game purposes that it'd be a good idea to make twin habitables more common.

Moon	General Planet Type
Size	Mass 2/3 Rocky	Type G	Type I
3 ("mass2 twin")	01	01	01
2 (large "mass1" moon)	02-06	02-20	02-10
1 (average moon)	07-100	21-100	11-100

Also note that Type G planet moons would normally be be Type B moons, unless the G were to be in the Rocky Zone in which case its moon type would be similar to those of a mass 2/3 planet at the same distance, meaning that Type B or H moons, or possibly even a Type T "mass 2" twin, or even a Type V "mass 2" twin, if the GG is sunward of the Biosphere (what I call the "Hot" zone).

For Type I planets, the moons would only be of Type F, though I'm not entirely sure that a "mass 2" Type F planet is all that possible. That'd be one freaking big ball of ice.

And for M2/3 Rocky planets, the moon types would be as per normal.


Also note that for the Rocky Zone this doesn't account for any possibility of alternative "minimal" planetary types which could possibly be in the mix.


Anyways.... just a few random thoughts...

[Crucis]

A few follow-up points and thoughts on the above table, as well as mutual tidelocking...

First of all, a moon size roll should be separate and done before any determination of mutual tidelocking. Furthermore, there are some process questions...

Should only the innermost moon have its size determined or all moons? From a realism standpoint, moon size should probably be done for all moons, not just the innermost one, as 2 of Jupiter's moons (Ganymede and Callisto) would qualify as "large moons". From a simplicity standpoint, I'd probably suggest that moon sizes should be determined before assigning orbits, and then sort the moons by size from largest to smallest, with the largest moons being closest to its planet. This would make moot any issue of having a Rocky planet with a true "twin" in an orbit other than the innermost orbit, which might actually cause the planet and its twin to MTL and cause any moons inside of the twin's orbit to be lost.

Then after determining moon sizes (and sorting of the moons by size), you can determine lunar orbits with the normal orbital rolls.

After that, any mutual tidelocking would be determined. MTL is only an issue for Rocky planets. If the innermost (and hence, largest) moon is "large" or a "twin", the rocky planet is automatically MTL'd. But if the innermost moon is only average in size, then the chance that the planet is MTL'd is only 40% (1-4 on 1d10).

[aramis]

I was wondering if this and Brown Dwarves would be addressed...

If it can be kept simple to do, great. But I'm already lost by the (GSF/Ultra?) type codes...

[Crucis]

I was wondering if this and Brown Dwarves would be addressed...

There are a number of anomalous situations like that that "could" be addressed. There are a number of issues with such anomalous planets and stars, not the least of which is increased complexity, of course. This is one of those things that comes up when one is considering the balance between simplicity and complexity (i.e. increased detail).

If it can be kept simple to do, great. But I'm already lost by the (GSF/Ultra?) type codes...

Actually, the GSF/Ultra planetary type codes are pretty similar to those in 3e, which are pretty similar to the original codes in 2e's New Empires.

In large part, the biggest gripe I have is the Type O1/2/3 codes (Type O in 2e with no distinctions) which are entirely non-intuitive. 3e split Type O into Types O1 and O2, and 3e split O1 into O1 and O3. I'm simply going to replace O1/2/3 with Types H (for Hot), B (for Barren), and F (for Frozen). Simple and hopefully, intuitive.

[aramis]

Having seen those explained, yes, F#/B#/H# far more intuitive. Will we see similar for T & V?

[Crucis]

Having seen those explained, yes, F#/B#/H# far more intuitive. Will we see similar for T & V?

Actually, it's just Type H, B, or F for planetary codes (instead of O1, O2, and O3) for the moment. No "#" numbers following the code. Codes for moons are currently Types mH, mB, and mF, with the little 'm' used for "moon". Also, currently, there are 3 types of asteroid belts, Types aH, aB, and aF, with the little 'a' indicating an asteroid belt of the H, B, or F type.

All of the other planetary types will likely remain unchanged, though it is somewhat possible that types T and ST may be merged into a single type. Types, V, G, and I will remain as is. If Hot Jupiters were to exist in the rules, they'd likely just remain as Type G planets, rather than have a separate code. At the moment, the only reason I can see for requiring a separate code for HJ's is if Unusual Race rules exist, since I'm thinking that normal gas giant races wouldn't find an HJ to be entirely compatible. But without such rules, there seems little reason to worry about a separate type code for HJ's. "Hot Jupiters" would simply be gas giants in the rocky zone, though, of course the types of their moons would be affected by the planet's proximity to the star.