Re: GURPS Space - assistance
 

You have not yet mentioned any accretion disk around your black hole and that is almost certainly its' most important characteristic in this scenario. You need for there to be virtually no disk to limit hard radiation to acceptable lavels.

You also need for these two bodies to have formed at realtively distant places in space and tiime. Co-evolution is not really an option. There was a large supernova (and maybe even a hypernova/gamma ray buster) at that black hole's location just slightly before its' formation. It may have eaten a star or two afterward as well.

All very interesting as long as it takes place at a safe distance but a safe distance is probably rather more than 600 AU.

The capture of Astra's solar system by Thantos needs to have happened well after planetary formation and never brought Astra's planets too close to Thanatos. Otherwise you get accretion disk and radiation problems and might well have problems with a highly elliptical orbit long afterwards.

I suspect that there is some gentle long range capture scenario that meets your needs but it will be another low probabitliy occurence.

The good news is that the requirements for post-planetery capture does away will all considerations about how Thanatos would have affected Astra's developing solar system. There was no effect at all because it wasn't there at the time.

If Thanatos and Astra had started forming around the same time at a distance of 600 AU, Thanatos would have gone boom before Astra really got started and the supernova would have blown away too much of the gas and dust Astra needed to make a solar system.

Recent (in astronomical terms) supernovas of the correct type that we know of tend to have largish accretion disks and intense radiation too. Mnay of them even form pulsars. You really don't want to be 600 aU from a pulsar.

Thanatos has had a violent past and that all needs to have taken place more thaa 600 AU from Astra. Probably quite a long time in the past as well. Even now Thantos would be doing nasty things to Astra's Oort Cloud.

Re: GURPS Space - "desert planet"
 

Possibly. If you start with a nice thick atmosphere to convect plenty of heat to the cold side, and if you start out with so much water that there is still plenty on the sunny side after the formation on the shady side of an ice cap fifteen times the size of Antarctica. I suspect that the rule for synchronously-rotating planets on Space p.125 may be generous in the matter of the effect on hydrographics. I'm pretty sure that it does not take into account that the ocean will freeze solid on the shadyside, so final hydrographics figures should be cut in half after the present adjustment.

Re: GURPS Space - "desert planet"
 

Does this take into account "superrotation" of the atmosphere? Most of the habitable tide-locked planet scenarios I've seen appear to require somethiong like a planetwide tradewind blowign at 30 mph all day every day (for Earth-standard values of "day").

They allso seem to require that the superroatation just fall into a "Goldilocks" range and stay there without any as yet proposed regulation method.

All sounds unlikley to me but proponents emphasize that it might be _possible_.

Re: GURPS Space - assistance
 

Life will likely pop up anywhere you have water and some energy gradient.
Getting it to be even vaguely earth like in weather is a bit less likely.
But with how many red dwarfs there are, the unlikely becomes a near certainty somewhere.

I still like the concept so much, I would have to put at least one colonized/studied tidal lock world for fun and weird life.

Re: GURPS Space - "desert planet"
 

I wouldn't say "profusion". They can exist, but with the inner limit size penalty and the narrow habitable zones of red dwarfs, I don't see a lot of them.

Re: GURPS Space - "desert planet"
 

I'm going by Merlis, T.M. and Schneider, T., 2010 Atmospheric dynamics of Earth-like tidally locked aquaplanets. Detailed results depend on how fast the orbit is, because in a small orbit (as around a late star) the tidally-locked world is still rotating fast enough to have significant Coriolis effects. Merlis & Schneider consist (as extremes) the 24-hour and the 8760-hour orbits. I would be interested in similar investigations of intermediate values if any were available.

The 8760-hour orbit gives a weather pattern that is roughly symmetrical about the subsolar point, with winds blowing directly from sunnyside to shadyside (i.e. no super-rotation). Shadyside is pretty uniformly between 240 K and 250K.

The 24-hour orbit gives a super-rotating jet at the equator, up to 45 m/s (100 mph), with much more structure to the temperature pattern over shadyside. But still ends up with the temperature on the shady side well below 260 K. Even taking into account the rotation of the planet and the ciculation of the atmosphere, on shadyside water is a rock-forming mineral and snow is a form of sand.

Re: GURPS Space - "desert planet"
 

I see a great many. In my 10,000-star run they came in as about half of all "habitable" planets.

Re: GURPS Space - assistance
 

So much cool discussion here.

I had considered Thanatos becoming a black hole and swallowing other stars far away from and much earlier than the Astra system forming, and then they both just happened to come into gravitational contact with each other when migrating through the galaxy from different locations and directions if necessary. Low probability is remotely possible and rare. That works for me.

As far as Thanatos still doing nasty things to Astra's oort cloud, I was hoping that would be the case. I wanted locals and vistors to the Astral system to have a general sense of fear and dread regarding Thanatos being in relatively close proximity. Oort clouds are already so dark and spooky even without a massive black hole beyond. Interstellar navigators, take the long way around.

Re: GURPS Space - gas giant arrangement
 

I hadn't read all of that early migration in and out of Jupiter and Saturn. Cool. But does this mean that the book's formula for calculating snow lines is incorrect or out-of-date? On p.106 it says R = 4.85 x square root of L. According to the chart on p.103 has the L-Min for a G2 as .68. So according to the book, Sol's snow line would be (4.85 x square root of .68), about 4 AU.

Re: GURPS Space - "desert planet"
 

http://www.astrobio.net/exclusive/41...‘dune’-planets-

I thought this was an interesting line of speculation regarding the likelihood and habitability of "land class" planets.