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The Supreme Canuck
2009-Jan-14, 04:17 AM
I'm working on a little bit of science fiction, and I want to keep it as "hard" as possible. So I need a little information.

Much of the action is going to take place in the Struve 2398 (http://en.wikipedia.org/wiki/Struve_2398) system, notably on a planet orbiting within the habitable zone of Struve 2398 B. Now, this star is a red dwarf and a flare star. Since it is so weak compared to Sol, a habitable planet would sit in an orbit about 0.15 AU from the star - which means it would probably be tidally-locked. Which leads me to the first question:

I need the planet to have an atmosphere of some sort - but not necessarily of the same composition as or at a comparable pressure to Earth's. Is it possible for a tidally-locked planet to retain such an atmosphere and also remain at relatively livable temperatures? I've read that convection can allow for both, but I'd like a confirmation.

The reason that I put my planet in orbit around Struve 2398 B is that I want it to have a native lifeform that relies on the extra radiation during a flare. That leads to the next question:

How often does Struve 2398 B flare and, generally, at what intensity? Not being an astronomy major, I haven't a clue where to go for that information - if someone could point me in the direction of a table of observations of the star over time, that would be ideal. The amount of time I get between flares seriously impacts how the native flora and fauna are going to behave.

Another concern is that flare stars often put out an unhealthy amount of radiation (especially x-rays) during a flare. Which is especially bad for a planet only 0.15 AU away. Now, I'm not too worried about my alien beasties being able to survive it, but putting people on the planet may be an issue. And so to the final question:

In general, how much x-ray or other harmful radiation does Struve 2398 B emit during a flare, when measured at a distance of 0.15 AU? Better yet, where can I find the numbers, and how do I figure it out myself? Are my characters going to get fried during a flare, or can they survive, even if it isn't comfortable? Or is it completely a non-issue?

Sorry if this all seems elementary, but I don't know where to look for the information I want. Astronomical data and tables are kind of out of my area of expertise.

The Supreme Canuck
2009-Jan-15, 12:11 AM
No takers, eh?

Right. Let's do it one question at a time, then. Can a tidally-locked planet retain an atmosphere (that is, without it freezing on the dark side) and maintain temperatures that aren't totally ridiculous (say, -50 C to 200 C)?

I suspect that it is possible, as convection in the atmosphere would distribute the heat from the sun, preventing the atmosphere from freezing and the sunny side from getting too hot. Am I right in assuming this?

StupendousMan
2009-Jan-15, 12:38 AM
I'm working on a little bit of science fiction, and I want to keep it as "hard" as possible. So I need a little information.

Much of the action is going to take place in the Struve 2398 (http://en.wikipedia.org/wiki/Struve_2398) system, notably on a planet orbiting within the habitable zone of Struve 2398 B.

It's hard to find information on the flaring frequency for this star.
This star has many names: this page from SIMBAD lists some
of them:



SIMBAD infor on this star.
(http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%40286486&Name=LHS%20%20%20%2059)
The most useful may be LHS 59, or G229-14.

I asked for a list of all papers in the astronomical literature which
contained some reference to this star, and which have the
word "flare" in their title. You can find the list here:

click to see the list (http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PRE&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&obj_req=YES&aut_logic=OR&obj_logic=OR&author=&object=LHS+59&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=flare&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1)

I don't have time to look at them for you, alas. But perhaps you
or someone else will.

Good luck.

The Supreme Canuck
2009-Jan-15, 12:42 AM
StupendousMan, that's... stupendous! I'm sure I'll find the answers to my second and third questions in there somewhere. If nothing else, it'll make for interesting reading. Thanks a lot for pointing me in the right direction.

eburacum45
2009-Jan-15, 01:00 AM
No takers, eh?

Right. Let's do it one question at a time, then. Can a tidally-locked planet retain an atmosphere (that is, without it freezing on the dark side) and maintain temperatures that aren't totally ridiculous (say, -50 C to 200 C)?

I suspect that it is possible, as convection in the atmosphere would distribute the heat from the sun, preventing the atmosphere from freezing and the sunny side from getting too hot. Am I right in assuming this?
The program makers of the National Geographic programme Alien Worldswere convinced that such a planet could retain an atmosphere.
See here
http://en.wikipedia.org/wiki/Aurelia_and_Blue_Moon#Traditional_assumptions_test ed

Nonetheless, the scientists employed by the programme decided to test the traditional assumptions for such a planet and start a model out for it from a proplyd through to its eventual death. Their estimations suggested such a planet could indeed hold on to its atmosphere, although with freakishly unusual results by Earth standards. Half of Aurelia would be in perpetual darkness and would be in a permanent ice age. The other half would contain a giant, unending hurricane with permanent torrential rain at the point directly opposite the local star. In between these two zones would be a place suitable for life. I think that means that a circular band between the terminator and the hurricane could be habitable, although not necessarily for Earth life.

(here's a pictue of a similar planet I made recently)
http://eg.orionsarm.com/im_store/bullseye.jpg

The Supreme Canuck
2009-Jan-15, 01:28 AM
That more or less accords with what I've read, thanks. One further question, though; could I do without the storm? Say, if there is a very low amount of atmospheric H2O?

eburacum45
2009-Jan-15, 04:48 AM
Another planet I've made has a drier sunward face, and a higher average temperature; the only habitable regions are a thin band near the terminator
http://www.orionsarm.com/worlds/Dante.jpg
Perhaps it too has a sunward cyclonic storm, but if the air is too hot and dry the storm will be a duststorm instead. But any world with a biosphere will need water, and most of the water on such a world will probably be frozen on the cold side.

I should think that the density of the atmosphere plays a very great part in redistributing the heat around the planet. On a planet with a thick atmosphere the heat (and water vapour) will be redistributed more efficiently than on a planet with a thin atmosphere.

Here's a few more references;
------------
http://martianchronicles.wordpress.com/2008/03/18/fire-and-ice-tidally-locked-exoplanets/
mentions molten rock on a very hot planet, which nevertheless might have an 'annulus' of temperate conditions. Annulus; that's a good word.

----------
Here's a simulation of the rotation of the atmosphere on the tidally locked gas giant HD 209458b
http://arxiv.org/PS_cache/astro-ph/ps/0209/0209227v2.fig1.jpg
perhaps a tidally locked terrestrial with a very thick atmosphere might display similar assymetric patterns.

.
.
.

The Supreme Canuck
2009-Jan-15, 05:31 AM
This (http://www.treitel.org/Richard/rass/tidelock01.txt) page, which references an article that I can't get my hands on, indicates that a planet roughly the size of Earth with either a CO2 or Nitrogen based atmosphere at around 1 atmosphere of pressure would have reasonable temperatures on both sides of the planet, with hot air travelling along the equator in both directions to the other side and cold air returning over the poles. Even a very thin atmosphere seems to work.

Anyway, I think I can work with what I've got, here. A thinner atmosphere should remove a bunch of water from the equation, so I won't have a raging tempest to deal with. Thanks a lot.

Grashtel
2009-Jan-16, 05:17 PM
This (http://www.treitel.org/Richard/rass/tidelock01.txt) page, which references an article that I can't get my hands on, indicates that a planet roughly the size of Earth with either a CO2 or Nitrogen based atmosphere at around 1 atmosphere of pressure would have reasonable temperatures on both sides of the planet, with hot air travelling along the equator in both directions to the other side and cold air returning over the poles. Even a very thin atmosphere seems to work.
I did a quick Google Scholar search (http://scholar.google.co.uk/scholar?num=20&hl=en&lr=&safe=off&cluster=737957849112835111) finds the paper in a freely available form here (http://crack.seismo.unr.edu/ftp/ftp.saved/pub/gillett/joshi.pdf) (warning PDF download).

grant hutchison
2009-Jan-16, 06:08 PM
The following doesn't deal with your star specifically, but it provides some discussion of conditions in the habitable zone around a flare star.
Buccino et al.: UV habitable zones around M stars (http://arxiv.org/abs/astro-ph/0701330).

Grant Hutchison

The Supreme Canuck
2009-Jan-16, 06:38 PM
I did a quick Google Scholar search (http://scholar.google.co.uk/scholar?num=20&hl=en&lr=&safe=off&cluster=737957849112835111) finds the paper in a freely available form here (http://crack.seismo.unr.edu/ftp/ftp.saved/pub/gillett/joshi.pdf) (warning PDF download).

Okay, that's just odd. The only thing I got from Google was a link to pay for a print version of the thing. That's incredible, thanks.

Grant: That's a big help, too, thanks.

Sock puppet
2009-Jan-26, 01:05 PM
Okay, that's just odd. The only thing I got from Google was a link to pay for a print version of the thing. That's incredible, thanks.

I'll wager Grashtel is in a university or library which pays for the journal subscriptions. If they do it properly, you never even notice you're getting material you'd normally have to pay for.

PM me an email address if you want me to send you the paper :)

Grashtel
2009-Jan-26, 01:33 PM
I'll wager Grashtel is in a university or library which pays for the journal subscriptions. If they do it properly, you never even notice you're getting material you'd normally have to pay for.
So just how much do you want to wager on that? I could use some more cash :D

I am a university student but I very rarely post from there, those links were found and accessed from home (and no I don't live in uni accommodations either).

Grashtel
2009-Jan-26, 01:36 PM
Okay, that's just odd. The only thing I got from Google was a link to pay for a print version of the thing. That's incredible, thanks.
Were you trying plain Google or Google Scholar? Google Scholar is much better when it comes to looking for academic materials like that paper rather than just general web searches.

Sock puppet
2009-Jan-26, 10:25 PM
*Slowly realises that he misread Canuck's post*

I thought you couldn't access that paper that Grashtel linked, nevermind.

As for the wager, why don't we LOOK OUT BEHIND YOU! *runs away*

Starfury
2009-Jan-26, 11:43 PM
An intriguing idea, and, as other posters have said, well within the realm of possibility.

The sky of such a planet would be red, regardless of the composition of the atmosphere, because of the planet's proximity to its primary star.

If the planet were denser than Earth, it might be able to generate a stronger magnetic field to deflect some of the star's flare output.

In any case, any higher life form that did evolve on such a planet would have the evolutionary mechanisms to cope with the internal and external enviromental factors mentioned. They might even, as you suggested Canuck, depend on the extra radiation in some way.

Other info you might find useful:

Struve 2398B is an M5 dwarf star whose average separation from Struve 2398A is 59.42 AU.

Ken G
2009-Jan-27, 05:45 AM
Is it possible for a tidally-locked planet to retain such an atmosphere and also remain at relatively livable temperatures? I've read that convection can allow for both, but I'd like a confirmation.I wonder if the Alien Worlds and other calculations cited have taken an Earth-like atmospheric pressure as an initial condition and asked if it could be sustained, not considering that you also need to know if such an atmosphere could be generated. I'd be worried about a chicken-and-egg problem: perhaps convection could share the heat well enough to keep the atmosphere from boiling off on the hot side or freezing away on the cool side, but only once the atmosphere was thick enough to be an efficient conduit for heat! If the atmosphere was trying to form relatively gradually via volcanic outgassing or accumulation of bombarding material, it might not be able to escape these fates until it was sufficiently dense, so it might be unable to ever get to that point.


In general, how much x-ray or other harmful radiation does Struve 2398 B emit during a flare, when measured at a distance of 0.15 AU? Better yet, where can I find the numbers, and how do I figure it out myself? Are my characters going to get fried during a flare, or can they survive, even if it isn't comfortable? Or is it completely a non-issue?
I didn't see if this was covered, but I believe a thick atmosphere is generally quite a good shield against harmful flare emissions. Whether or not each event might "boil off" part of the atmosphere is another issue, but I would guess less of an issue than the problem of simply getting a thick atmosphere in the first place.

eburacum45
2009-Jan-27, 06:16 PM
The sky of such a planet would be red, regardless of the composition of the atmosphere, because of the planet's proximity to its primary star.
That may be an oversimplification. The light from many red dwarfs contains enough blue light for scattering to be significant; here is a chart which shows one interpretation of the data, note that many red stars produce whitish, yellow or orange skies instead.
http://chaos-syndrome.deviantart.com/art/Star-and-Sky-Colour-Chart-61888191

Struve 2398 B is brighter than Proxima, so would probably have a pink/yellow sky, like the one shown for Barnard's star.

Starfury
2009-Jan-27, 08:04 PM
Very interesting, thanks for pointing that out. I think I'd enjoy living under a pinkish-yellow (or yellowish-pink) sky.