SFRPG
http://sfrpg-discussion.net/

Expanded UWP (Cepheus)
http://sfrpg-discussion.net/viewtopic.php?f=30&t=3224
Page 2 of 2

Author:  thrash [ Wed Sep 13, 2017 1:41 pm ]
Post subject:  Re: Expanded UWP (Cepheus)

Cyborg IM1 wrote:
SIZE
Size only goes to A (10000 mile diameter) but there are known exoplanets that are larger than that. So, if we simply expand it to B and C, we can cover them. The question I have on SIZE is does it realistically need to go higher than C (12000-13000 mile diameter)? At some point, it is going to become a small gas giant, so there should be a natural upper limit. BUT, if the world is located in the Inner Zone (inside the habitable zone), there will be essentially no volatiles and so forming a Gas Giant would be much harder, so a larger rocky world (or an exposed Gas Giant core) could exist (I think). While it is no big deal either way to me, I want to make sure I am accounting for all logically possible worlds, based on what we know today, but not add sizes that are really not possible.

If you're serious about this project, you should probably read up on the latest theories of planet formation. I've linked two useful review papers here.

In this case, you should realize that giants (gas or ice) are not thought to form in the inner zone. They form out beyond the snow line and migrate in to the edge of the protoplanetary disk, potentially due to one of several possible mechanisms. Note also that stars get brighter as they age, so any "zones" move outward over time.

Really, the discovery of hot jupiters has rendered the whole concept of inner and outer zones somewhat moot. Habitability is also more difficult to define, in that the habitable zone derived from analytics isn't wide enough to account for the evidence of possible habitable conditions on Mars (and perhaps Venus, too, albeit even more briefly).

Author:  thrash [ Wed Sep 13, 2017 1:48 pm ]
Post subject:  Re: Expanded UWP (Cepheus)

Cyborg IM1 wrote:
Not much to change here, the values and reasoning make perfect sense for a world in the Habitable Zone. For world in the OUTER zone, on the other hand, it fails miserably. Even LBB5 screwed this up as they listed Europa as HYD 0, even though they KNEW it was covered in ice.

Bodies that form beyond the snow line aren't so much covered in ice as primarily composed of it. Water ice is very abundant, and at these temperatures is a mineral. You may as well say that Earth's surface is 30% covered by silicate "ices." You also run into the problem of which ice are you talking about? Pluto's surface is mostly composed of ices, but there are several species with very different characteristics.

Author:  EDG [ Thu Sep 14, 2017 5:26 pm ]
Post subject:  Re: Expanded UWP (Cepheus)

thrash wrote:
Really, the discovery of hot jupiters has rendered the whole concept of inner and outer zones somewhat moot. Habitability is also more difficult to define, in that the habitable zone derived from analytics isn't wide enough to account for the evidence of possible habitable conditions on Mars (and perhaps Venus, too, albeit even more briefly).


In my generation system the snow line at system formation was what determined the point beyond which jovians could form, then they migrated in after that. I think after that the inner and outer zones are still handy reference points though - what's missing in Traveller is the Middle Zone, which is between the outer edge of the Habitable Zone and the inner edge of the Outer Zone - a zone that is too cold to be habitable for most earthlike worlds, but is still within the snow line so isn't dominated by ice.

Author:  Cyborg IM1 [ Wed Sep 20, 2017 10:39 pm ]
Post subject:  Re: Expanded UWP (Cepheus)

Thanks for the comments!

EDG, one question is could a world with a Dense, Tainted Atmosphere (tainted with CO2) have liquid water near the Snowline, for example, if the Asteroid Belt was a large world with a dense atmosphere, could it have liquid water?

What is the REAL differnce between the Habitable Zone and the Middle Zone?

Author:  EDG [ Thu Sep 21, 2017 7:01 am ]
Post subject:  Re: Expanded UWP (Cepheus)

Broadly speaking, "The inner edge of the HZ is the distance where a runaway greenhouse effect vaporizes the whole water reservoir and,[10] as a second effect, induces the photodissociation of water vapor and the loss of hydrogen to space. The outer edge of the HZ is the distance from the star where adding more carbon dioxide to the atmosphere fails to keep the surface of the planet above the freezing point.[10]"
(from https://en.wikipedia.org/wiki/Circumste ... ermination )

In practice, I think Traveller defined the habitable zone to be between about 0.9 and 1.4 * SQRT(Luminosity) AU. This left a big gap between the outer edge of the habitable zone and the Snow line that marked the start of the Outer Zone (usually at around 2.5-3 * SQRT(Luminosity) AU). That gap is the Middle Zone, where it's too cold for habitable earthlike worlds but not cold enough for ice and gas to dominate over rock.

Theoretically a big enough world with a dense enough CO2 atmosphere might have habitable temperatures and liquid water in the Middle Zone, though the amount of CO2 present would make the atmosphere rather unbreathable.

Author:  Cyborg IM1 [ Tue Sep 26, 2017 2:58 pm ]
Post subject:  Re: Expanded UWP (Cepheus)

Perfect, that is EXACTLY what I was looking for! :)

So, 4 zones, but many of the characteristics of the world (other than atmosphere and hydrographics) would be similar in the Habitable and Middle zones.

My generation system is going to assume that any planetary migration has already occured, so even though gas giants will only form in the Outer Zone (beyond the snow line), many will migrate inward.

So, the chances of a gas giant being located in each zone will change, becoming smaller as you move IN.

I also agree with Ismael about the water/ice thing. I just need to drop that and if a world is in the middle or outer zone, it has ice - nuff said.

Page 2 of 2 All times are UTC
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/