SFRPG

The forum for Science Fiction Role Playing Game inspiration and information! So Say We All!
It is currently Fri Jan 19, 2018 1:17 am

All times are UTC




Post new topic  Reply to topic  [ 13 posts ]  Go to page 1 2 Next
Author Message
 Post subject: Tidelocking redux
PostPosted: Sun May 26, 2013 9:47 pm 
Offline
Administrator
User avatar

Joined: Thu Jul 03, 2008 1:22 am
Posts: 5296
I just ran over all my tidelocking equations again, and by making reasonable assumptions about the planets' internal properties, I'm finding that any habitable planet (earth-sized or greater) in the habitable zone of a star of 0.7 solar masses or less (which is anything from a K4 V to M9 V) will be tidelocked within about 250 million years of formation. So in practice, that means that any earthlike planet around those stars will be tidelocked, and most of the time in any SF setting we'd probably be visiting them long after they've reached that age. And any planet in or within the habitable zone of a red dwarf (M V) will be tidelocked, period.

Interestingly, a world like the Earth tidelocks in about the same time as a rocky superearth that is bigger, denser, and more massive (6 earth masses). A panthalassic superearth on the other hand (bigger, lower density, more water, about 3 earth masses) tidelocks more quickly. Mars-sized worlds in the habitable world take longer to tidelock because they're smaller - they'd only be tidelocked within a billion years around stars with < 0.6 solar masses (K6 V - M9 V).

No planet ever tidelocks in the habitable zone of a star with equal to or greater than 1 solar mass or higher - it's too far from the star.

There may be exceptions - odd internal structures, more/less molten planetary interiors, superdense atmospheres being affected by solar tides, influence from other planets etc. But taking the star and the planet alone, this is what would happen. As a note: tidelocked planets will not have big moons either - solar tides would cause the moons to crash into the planets pretty quickly.

I also haven't tried putting in different superearths (higher mass panthalassics, lower mass rocky ones, etc). That could be interesting, but I think the general trend will still hold - big planets will still be tidelocked pretty quickly.

_________________
SFRPG Owner/Admin
This post (or any other post I made here) may not be quoted or copied beyond the SF RPG boards without my explicit permission.
Check out the latest news from Spica Publishing!
evildrganymede.net - visit the The Worldbuilding Hub, and check out my Science Blog!


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Mon May 27, 2013 8:53 am 
Offline
User avatar

Joined: Thu Jul 03, 2008 1:08 am
Posts: 3107
Location: Sonthofen / Germany
EDG wrote:

No planet ever tidelocks in the habitable zone of a star with equal to or greater than 1 solar mass or higher - it's too far from the star.

Good to know, this means that I do not have to do the calculations for
the main planet of my current setting - thank you. :)


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Mon May 27, 2013 3:05 pm 
Offline
User avatar

Joined: Tue Dec 28, 2010 5:54 am
Posts: 214
Hmm...looks like I need to tack this onto the day length rule in my star system building rules.

_________________
The Gray Book: My homage to E.G.G.

Star Trek: Alpha Quadrant: The game Mongoose failed to make. (File Updated 5/19)


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Tue May 28, 2013 2:15 pm 
Offline
User avatar

Joined: Tue Jul 08, 2008 8:42 pm
Posts: 2667
Location: Texas, USA
Thanks for posting this! I think that makes for some easy assumptions/rules.

_________________
My friends call me Richard. You can call me Sir.
www.XmasDragon.com


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Thu Aug 21, 2014 12:51 am 
Offline
User avatar

Joined: Thu Aug 01, 2013 3:15 am
Posts: 70
A large, close satellite could prevent tidelocking with respect to the star. Dole discusses this in Habitable Planets for Man.

_________________
I am not expendable, I'm not stupid, and I'm not going.


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Thu Aug 21, 2014 6:20 am 
Offline
Administrator
User avatar

Joined: Thu Jul 03, 2008 1:22 am
Posts: 5296
I never did get the hang of what big satellites do regarding solar tides. I think what happens is that without the satellite, the star would be trying to slow the planet rotation down (and the planet would slow the star's rotation down very very slightly in the process). When a satellite is there, it's trying to slow the planet rotation down to equal the satellite orbital period - and it's slowing the planet rotation down faster than the star is slowing it down. So the planet-satellite system would probably get into equilibrium first, with the moon tidelocked to the planet, then the planet rotation tidelocked to the lunar orbital period (and the moon would be pushed outwards in the process). I think the stellar tides would serve to slow the rate that this happened over time.

When those are in equilibrium, the star would be able to start pulling more angular momentum out of the system, which would slow the planet rotation to match its orbital period around the star. In doing so, the moon would be pushed out even further (since it's locked to the planet and has to match the planet's slowing rotation), and eventually it would probably leave the stable part of the planet's Hill Sphere and become a separate body orbiting the star. At that point the star can slow down the planet without the satellite being there. I think?

So yes, I think it'd at least delay the tidelocking of the planet to the star ;)

_________________
SFRPG Owner/Admin
This post (or any other post I made here) may not be quoted or copied beyond the SF RPG boards without my explicit permission.
Check out the latest news from Spica Publishing!
evildrganymede.net - visit the The Worldbuilding Hub, and check out my Science Blog!


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Fri Aug 22, 2014 12:47 am 
Offline
User avatar

Joined: Thu Aug 01, 2013 3:15 am
Posts: 70
Habitable Planets for Man is available online if anyone wants to read Dole's take on it. See pp. 72-75.

I don't have a firm grasp of the concept. I'm just trying to find more rotating worlds in the habitable zone. ;)

_________________
I am not expendable, I'm not stupid, and I'm not going.


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Fri Aug 22, 2014 2:11 am 
Offline
Administrator
User avatar

Joined: Thu Jul 03, 2008 1:22 am
Posts: 5296
Keep in mind that Dole's work is from 1964. Our understanding of Orbital Dynamics has evolved considerably in 50 years... (I think that's even before Goldreich's seminal paper on the subject).

The bit I was stuck on was what happens to the planet-satellite system after the satellite gets tidelocked and synclocked to the planet (like Pluto-Charon is). I'm not sure the satellite would necessarily just keep going outwards - I think it'll start moving inwards as momentum is sucked out of the planet-satellite pair into the planet-sun system.

These papers look like they could shed some light on that:
Obliquity evolution of extrasolar terrestrial planets (2007): http://arxiv.org/abs/astro-ph/0611669
A dynamical study on the habitability of terrestrial exoplanets I: Tidally evolved planet-satellite pairs (2012): http://arxiv.org/abs/1210.1640

_________________
SFRPG Owner/Admin
This post (or any other post I made here) may not be quoted or copied beyond the SF RPG boards without my explicit permission.
Check out the latest news from Spica Publishing!
evildrganymede.net - visit the The Worldbuilding Hub, and check out my Science Blog!


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Wed Sep 03, 2014 3:28 am 
Offline
User avatar

Joined: Thu Aug 01, 2013 3:15 am
Posts: 70
EDG wrote:
Keep in mind that Dole's work is from 1964. Our understanding of Orbital Dynamics has evolved considerably in 50 years... (I think that's even before Goldreich's seminal paper on the subject).


It's still a classic. It's almost essential for any world builder. I remember back in the early 80's I went to the university library and photocopied about half the book. I couldn't figure out why the stellar data didn't match the data in Book 6. GDW didn't give their source. That was my first lesson in astrophysics - There's plenty of room for fudging ;)

Quote:
These papers look like they could shed some light on that:
Obliquity evolution of extrasolar terrestrial planets (2007): http://arxiv.org/abs/astro-ph/0611669
A dynamical study on the habitability of terrestrial exoplanets I: Tidally evolved planet-satellite pairs (2012): http://arxiv.org/abs/1210.1640


Thanks. I'll have to put them on my list of things to read.

_________________
I am not expendable, I'm not stupid, and I'm not going.


Top
   
 Post subject: Re: Tidelocking redux
PostPosted: Sat Sep 06, 2014 1:10 pm 
Offline
User avatar

Joined: Mon Dec 02, 2013 1:43 pm
Posts: 294
Location: Queens, NY
What would the impact of tidelocking be on a planet's magnetic field?


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 13 posts ]  Go to page 1 2 Next

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Limited