# Planet found in the Goldilocks Zone



## Ursa major (Sep 29, 2010)

> Astronomers have discovered a potentially habitable planet of similar size to Earth in orbit around a nearby star.
> 
> A team of planet hunters spotted the alien world circling a red dwarf star called Gliese 581, 20 light years away.


 


> One side of the planet is always facing the star, much as one side of the moon constantly faces Earth. This means that the far side of the planet is constantly in darkness. The most habitable region of the planet would be the line between the light and dark regions.


 


> The average temperature on the planet is estimated to be between -31 to -12C, but the ground temperature would vary from blazing hot on the bright side and freezing on the dark side.


From New Earth-like planet discovered | Science | The Guardian​


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## The Ace (Sep 29, 2010)

Interesting, maybe there'll be a few more soon.


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## The Judge (Sep 29, 2010)

I can't quite get my head round the conditions at this habitable region of which they speak.  I don't suppose there's a precise line, one side of which is absolute light, the other absolute dark, but what would it be like?  And if the planet wobbled a bit** in its orbit, would what had once been on the bright side then be plunged into the dark until it wobbled back again?

** I enjoy using technical terms... unfortunately, I don't know any


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## Vertigo (Sep 29, 2010)

As the planet is tide-locked the position of the sun relative to anyone stationary on the planet never changes.

Imagine you start on the sunny side and start moving towards the bright side. Initially you are in bright sunshine and it's probably too hot for any life. As you move towards the dark side (the force be with you) the sun will be gradually setting behind you, caused purely by your movment. You will slowly move into twilight and eventually into complete darkness where again there will pobably be very little life. I don't say none. In between the extremes there will be every possible environment from well below freezing to probably well above boiling (remember the temperatures given are averages for the whole planet).

Regarding wobbles. If the planet wobbles then the position of the boundary zone will also wobble. However planetary wobbles tend to have periods in the order of tens of thousands years. Plenty of time for any fauna or flora to migrate with them.

I'm no meteorologist but I would have thought a bigger issue would be the climatic consequences of having a stationary boundry with such radical temperature differences (orders of magnitude larger than from our poles to the equator). Not sure what effect that would have. A constant wind blowing to or from the boundary region maybe? And if so how strong might such a wind end up when it never stops blowing?

Come to think of it isn't that the kind of world Fuzzy Modem has in his graphic novel?


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## ScrambleEggHead (Sep 29, 2010)

Actually, your Honor - "wobble" is a technical term. Our moon is what keeps us from "wobbling" too much. Mars, on the other hand, wobbles a lot. Up to 60 degrees from what would be it's polar axis. It only has two very tiny moons - not much bigger than meteors - which it has managed to capture in it's orbit. 

I'm quite sure they don't have the technology to tell if the planet (mentioned in the first post) only wobbles slightly (they could probably tell if it wobbled a lot), and I doubt they can tell if it has a breathable atmosphere either. They would have to send a probe which would not produce concrete results for at least another 40 years, IMO. Unless the planet is made of concrete, in which case it will take even longer to produce those results. (Yes, that was a poor attempt at a joke). 

- EggHead.


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## Moonbat (Sep 30, 2010)

It would be strange to live in constant twilight, kind of spooky.
I suppose if live has evolved, and become sentient they will have no words for Dawn or dusk, or such words will be related to walking east or west. Interesting.


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## J-WO (Oct 1, 2010)

Day and night will be places to visit, not times of the day.

As one approaches the night side (before it becomes completely uninhabitable) the life there could be bio-luminescent like at the bottom of our oceans.


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## Dave (Oct 1, 2010)

Can someone more knowledgeable than me tell me? This planet would need an atmosphere for 'life as we know it, cap'tin'. If it is tide-locked there would be a huge temperature differential between one side and the other. Wouldn't that result in winds, so strong, that life could not survive?


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## chrispenycate (Oct 1, 2010)

I personally doubt an atmosphere (with or without  hurricane force winds).

Surely the dark 'pole' (technically, as the planet's rotation perfectly matches its orbit, it has a pair of perfectly good poles in the twilight zone; which, if you think about it, is where Earth's poles are, too, and look how cool they are, despite a higher average temperature and the insulating/heat diffusing properties if a layer of air. I suspect the 'habitable region' will be quite well into the bright.) will be cold enough to freeze anything but perhaps helium. 

Now, a thought experiment; we crash a comet somewhere on the bright side, and the energy from the impact and the local temperature evaporate most of its mass. Powee, we have an atmosphere; mostly carbon dioxide, methane and water vapour, but adequate for a start.

Unless we have an unbroken range of very tall mountains round the twilight, molecules are going to try and equalise the pressure, zoom off into the dark, and freeze.

Now, the first ones to freeze out are going to be water, so perhaps we could build that impassible wall of ice, so the rest of the volatiles stay where they are put, rather than a snow of dry ice (solid cee oh two) followed by a methane ocean, and finally solid methane, and a wobble or a slight angle of the axis of rotation relative to the orbit (though tidally locked, the moon does show slightly different portions of its face during its orbit, so we're not bound to thousands of years) could make seasonal glacial rivers, running down the ice face every year, to be replaced by snow from the moisture evaporating in the hot interior.

Anyone for tobogganing?


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## J-WO (Oct 1, 2010)

chrispenycate said:


> Unless we have an unbroken range of very tall mountains round the twilight, molecules are going to try and equalise the pressure, zoom off into the dark, and freeze.




How tall would these mountains have to be?


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## Vertigo (Oct 1, 2010)

They did state in the article that it has sufficient gravity to hold an atmosphere, so that suggests that it is quite likely. I think that an atmosphere would reduce the temperature differential considerably. 

Yes, there would certainly be a constant wind blowing and whilst I'm not sure how strong it would be, as it would likely be pretty constant I suspect life could evolve to handle it. Also I think that same constant wind would do much to prevent the extremes of temperature that Chris has suggested. They would certainly be more extreme that we are accustomed to but maybe not a stopper. My bigger concern would be all the moisture on the planet being locked up on the dark side. Over a period of time I suspect that almost all the water on the planet would end up as snow/ice on the dark side. There would simply be no water left at all on the hot side. Even in the twilight zone the moisture would gradually migrate to the darker side and get locked up.


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## RVM45 (Oct 3, 2010)

*Planet Building*

I watched a show on one of the educational channels--hmm, it's been some years ago now.

They laid out the following case:

Red Dwarf Stars are, by far, the most common.

[I remember reading that about one tenth of our Sun's mass is about as small as a Star can go and still ignite. I don't know what is the "Upper Cut-Off" for Red Dwarves...]

They thought for a long time that Red Dwarves couldn't have life-supporting Planets.

Then someone put forth a fresh burst of insight--and found that there was a rather narrow "Goldylock's Zone". It parallels the old proverb:

_"Indian build small fire, and stand close.."_

Standing that close has an interesting side effect--virtually all habitable planets will be locked in orbit, with one face perpetually turned to the Sun.

They concluded that since Red Dwarves are the commonest Star--by far; that Planets with one face perpetually in Sunlight, and the other perpetually in Darkness--may turn out to be the commonest type of habitable Planet--by far.

The only other universal that I recall about Red Dwarves,is that they all get cranky occasionally, have Beaucoup Sunspots, and spit out some massive bursts of Ultra-Violet--which would present challenges for any life on the Planet circling the Star--but not insurmountable ones.

The show went on to extrapolate how life might evolve on such a Planet--interesting, but the more specific it got, the less generally useful for Authors.

Well,even if the "Red Dwarf Planets" turn out not to be *The Most Common* habitable Planets, there still should be a plethora of them--and the perpetual day [or night] aspect makes them very interesting places to set off-world stories...

So my question is: "Has anyone else seen any factual discussions of these interesting Planets?"

And oh yes:

"Please tell me where."

.....RVM45


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## Precise Calibre (Oct 3, 2010)

*Re: Planet Building*

A very interesting concept.

From what I've been able to glean through the internet, you have several factors which could affect various aspects of the planet, depending on what you intended to do with it.

*****

As you said, planets linked to a red dwarf are tidally locked.  I've seen two schools of thought on this matter via wikipedia.  

First: Since the planets is tidally locked, this means that atmospheric gases and moisture will become trapped in the dark side of the planet, leaving the light side dessicated; this theory can possibly be countered by the presence of a large world-ocean with which heat can be cycled over the light side of the planet.

Second:  A theory was presented that if the dark side was home to many elements associated with a frozen atmosphere such as glaciers, these glaciers would migrate toward the twilight belt of the planet and be melted by the extreme temperature difference, allowing a gradual but persistent exchange of energy and resources on the planet, thus allowing the concept of planetary life to develop.   

*****

One issue which would most certainly have an impact on your world is the relative luminosity of a red dwarf.  From what I could find, the brightness of a red dwarf can be anywhere from 1/10th the luminosity of the sun all the way down to 1/10,000th.  It is said that the majority of a red dwarf's energy is radiated in the infrared spectrum.

Thus you have issues to take up for both indigenous life and for extra-planetary visitors.  

Humans visiting, colonizing or mining the planet would have to come prepared for life in what would seem to be perpetual twilight or even darkness.  In addition, the relatively low amount of radiation the planet would be receiving would require, in some situations, the preparation for dealing with extremely low temperatures.

Indigenous lifeforms, if we follow the earth-model of evolution would most likely have several common traits.  Regardless of whether or not they were intelligent, you would most likely see things such as:

--Large eyes for taking in more light in the dim environment

--No eyes or underdeveloped eyes if it is so dark that light is useless to ocular senses

--Enhanced aural senses - hearing might become the new "seeing" on this type of planet.

--Thick hides in colder-climate planets.

*****

As far as UV bursts go, I've seen a bit of contention on this matter.  It was basically argued that, while a UV burst could be potentially hazardous to the planets ecology, the atmosphere should be able to withstand such an assault.

*****


life span of a red dwarf - Google Search

life span of a red dwarf - Google Search

Ignore the fact that they both say "life span" it's two different searches .


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## chrispenycate (Oct 3, 2010)

*Re: Planet Building*

We're having a discussion on just this, down in science and nature http://www.sffchronicles.co.uk/forum/528975-planet-found-in-the-goldilocks-zone.html#post1432394

First I maintained that such a planet could not maintain a breathable atmosphere, as the cold end would freeze out everything but hydrogen and helium, and these being the lightest of gasses, the other constituents would be continually leaking in, and freezing. Particularly the water vapour, which has a tendency towards this even in our benevolent circumstances (as does carbon dioxide on Mars). Volcanic emission could counter this to some extent, but would you trust it to remain balanced over tens of millions of years?

Then, being me, I developed a mechanism to counter this.

If you start with a thick enough atmosphere (I suggested comet strike, but perhaps one of sufficient size would overcome the tidal lock temporarily, and set the planet spinning, which we don't want for this) then it pours out into the twilight zone, and the water vapour freezes out, forming an ice wall. In just a few centuries this is high enough that only the most energetic molecules make it to the top; and apart from hydrogen, most of them are water or methane.
As the wall gets higher, the atmosphere drops, until the entire high temperature zone is surrounded by a high, glassy wall of ice which holds back the heavier gasses and allows pressure to stabilise, the winds to cease. Outside this wall the plain shows concentric circles of compounds that have frozen out; starting with water and carbon dioxide and continuing through the entire range of components of a reducing atmosphere (there wouldn't be oxygen; free oxygen only arrives when life starts generating it); a massive target in space (but unlit, so no-one can see it. I wonder if any of those ices are coloured?)

Of course, with the slow rotation of a tidally locked planet we can't expect much in the way of magnetic field, so charged particles – solar wind, a few heavier molecules – will be sleeting down pretty well continuously, and far more so in the case of flares, so an underground habitat might be recommendable.

Hmm, I've never seen a reference book on this; you could try reading Pohl's "JEM", but he ignores the atmosphere problem all together. (He's really writing about politics and humans; the brown dwarf + planet is not very deeply explored.)


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## RVM45 (Oct 4, 2010)

*Re: Planet Building*

I've played with the idea of a tidally locked planet circling a Red Dwarf.....

While the Red Dwarf itself, orbits a Star about the size of our sun--about as far away as Mars.

One side always faces the dwarf--but the planet also gets supplemental sunlight, warmth from the big sun.

Granted, Mars would be pretty cold even if it had an atmosphere--but with a Red Dwarf parked in its back yard.....

.....RVM45        

Check this out:

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


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## RVM45 (Oct 4, 2010)

I was discussing this on another thread, when chrispenycate directed me here.

They had a brief dramatization of what kind of life you might have on such a planet, on one of the educational channels, a few years ago. I wish that I could remember the name of the show.

Anyway, they had a huge tornado as a permanent fixture--right in the precise middle of the bright center.

.....RVM45      

Here, check this out:

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


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## Vertigo (Oct 4, 2010)

Interesting Wiki article but I'm still not convinced that all water would not become locked up in ice on the permanent darkside. The process is really very simple any water vapour that strays to the dark side (as all water vapour eventually will at sometime in the history of the planet) will be frozen out of the atmosphere and locked on the surface. It is believed that the same thing has already happened on the Moon with all of its (surface) water locked up in permanent shade in craters at the poles: Lunar water - Wikipedia, the free encyclopedia


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## Nik (Oct 6, 2010)

"Libration Land", IIRC, is what you'd call the zone where slightly elliptical orbit would create day/night cycle.

As I see it, given a modest amount of CO2 as greenhouse gas, you'd have an ice-cap at the 'cold pole', with 'daily' thaw from the glaciers' margins providing run-off which feeds watercourses which eventually run out into the temperate libration zone. That area shades (no pun intended) into the hot zone, and the 'hot pole'.


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## Nik (Oct 6, 2010)

*Re: Planet Building*

Even tidal-locked, the orbit's ellipticity would provide 'libration lands' around the planet. Mind you, day/night would each be half a 'year', and you must think in terms of hot & cold poles...

More to the point, Mercury was long thought to be face-locked, but it isn't...


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## Doctor Crankenstein (Oct 7, 2010)

I saw an article about this yesterday. It's title was along the lines of: "Planet found with 100% chance of life!"

100% ? Science Journalism Fail.


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## chrispenycate (Oct 7, 2010)

> I was discussing this on another thread, when chrispenycate directed me here.


 …and has brought your thread along with you.

And if, like Mercury, the planet is not totally tidally locked but phase locked (harmonic multiples, very long days indeed), with every part of the surface going from baked to deep frozen, the odds of life developing there drop still further. Of course, when it is established (brought in from outer space?) it can find means of survival, either migrating continuously or generating tough spores; but the original conditions are not promising.

Nik, CO2 as a greenhouse gas won't work; it'll freeze out at minus 60°, and I'm expecting temperatures a _lot_ lower than that, Methane, perhaps, at minus 160°; it's a good greenhouse gas, but life would have to be anaerobic; difficult to maintain free oxygen.

In their "Aurelia" article  they say: 





> The show blurred the lines between science fiction and science fact.


 It's obvious that the writer doesn't read much science fiction; writing speculatively about new discoveries, new theories has been a major part of the output of the genre since its inception.


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## digs (Oct 7, 2010)

I heard that they'd discovered a 'potentially habitable' planet, but I didn't read far enough to get to the tide locked (am I using that right?) thing. How cool - imagine a planet where life can only exist in one thin strip of eternal twilight bordered by deadly 'day' on one side and 'night' on the other (I don't know how scientifically feasible that is, but just roll with me here). I would instantly be fascinated by any fictional book with that premise. Truly, what a wonderful world...that world must be.


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## Vertigo (Oct 7, 2010)

Chrispy, the atmosphere is an interesting chicken and egg problem really. If you have an atmosphere to start with then I suspect that same airflow from hot to cold that would migrate all the water vapour to the cold side to be frozen out, would, in turn, help mitigate the temperature difference. I don't know anywhere near enough about the physics but I suspect the bigger the temperature differential the higher the flow of warm 'air' to the cold side (and equally higher flow in the upper atmosphere back to the warm side). This would create a self-regulating system; the bigger the temp difference the higer the airflow, this reduces the temp difference and so reduces the airflow. This would naturally, eventually reach a steady state. The real question is what sort of temperature difference would that steady state give. I suspect it wouldn't be as severe as you suggest. It would certainly take all the moisture out of the air but I'm not sure about the CO2. Then the question for life is whether there is enough water to start with for the galciers to reach the boundary area and start melting, so providing moisture to that boundary area.

Re the chicken and egg thing, I think that it is not unreasonable for an atmosphere to have formed to begin with as the planet would not originally have been tide locked.

Another consideration is that without (significant) rotation I'm not sure how likely it would be to have a strong magnetic field and as I understand it our magnetosphere is one of the reasons we still have an atmosphere and Mars' lack of one is one reason it has lost most of its atmosphere. Without a magnetosphere a planet's atmosphere gradually gets stirpped away by the solar wind. At least that is my understanding.


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## chrispenycate (Oct 7, 2010)

Minus sixty isn't cold; you can get that at the poles on Earth, and they're not even totally dark.
But wind strength will not depend on temperature differential. I'm assuming it never gets cold enough to liquify hydrogen (if it does we've got problems maintaining an atmosphere at all) so the pressure differential evens out; the traditional air flows into the dark side under the lighter gasses, which partly mix, partly flow in to of it. So the process is not vast hurricanes, but gradual seep, which can't carry enough energy to do much about the really cold regions. 
Otherwise, we could try forgoing an atmosphere altogether, and going for a world ocean, some of which is frozen very solid indeed, but the pressure of extra snow on the surface would force to flow very, very slowly towards the temperate zones ( I prefer my towering ice peaks, clear out of the atmoshemisphere, and from the dark side gleaming ruby with refracted starlight. This 'wall' would also tend to reduce the tendency for the solar wind to sweep the atmosphere away.)

On the light 'pole' (please remember that the planet has a pair of perfectly traditional poles and an axis of rotation, around which it revolves once a year. It's just that they're a lot like anywhere else in the twilight, except for the movement of the stars) there are likely to be mountains, as the most massive point in the crust is the one most probably facing the star; and I would bet on vulcanism as common, since the core will be 'stirred' by the star's magnetic field. So you could get isolated pockets of warmth round hot springs on the cold side, and organisms using heat rather than light as a basic energy source, as round the deep ocean volcanic vents.


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## Moonbat (Oct 22, 2010)

I've been thinking about this for weeks, I find it very interesting. But I have a few questions, I wonder if one of you bright sparks could attempt to answer.

When the planet became face locked (tide locked or whatever the phrase is) was it a slow process, did its rotation slow down and eventually stop with days getting longer and longer until one lasted forever? Or would it have been a fairly quick process even an instant (unlikely) switch?

I have been trying to imagine the weather on such a planet, both Chris and Vertigo have been very useful, but I am still a little unsure as to what happens. Please forgive me ignorance but am I right in thinking:
The area closest to the sun heats up continuously
This causes the atmostphere at that point to heat up, which in turn causes the air to expand and so the pressure increases, but at the same time the air becomes thinner
The hot air then rushes towards the cold side where the pressure is less
The cold side of the planet loses all its heat (or most of it) to the coldness of space.
So the air is heated, moves to the cold side and cools, then it moves back to the hot side (but higher in the atmosphere) then get heated and repeats the process
This causes a mega storm to form on the hot side as the cold air is pulled into the storm from above and heated then expands out and rushes to the cold side.
Am I right in assuming that this process will settle down and become constant?
Will the air on the hot side reach a maximum temperature and equally a maximum pressure/expansiveness?
What do you get on the cold side that is the opposite of the megastorm, where warm air is moving to cool down and then moves vertically before returning in the upper atmosphere to the hot side? Is there an equivalent storm on the cold side, a reverse storm?

Wow, sorry for the all the questions, but the points made in previous posts have really piqued my interest.


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## chrispenycate (Oct 22, 2010)

Actually nobody knows if it starts with spin and this cancels out with time (lots of time, hundreds of millions of years, that's a big top running down, lots of energy) or whether, ile the planet is actually forming from infall of the protoplanetary disc all the rotational energy is taken up then (is that clear? As a dust cloud, I see.).

What seems likely is that it forms and locks without an atmosphere, and that is added later, either by collision with a good source of volatiles (think comet) or by outgassing from the interior. One gives us instant, extremely agitated gas, the other is a slow cumulative effect (difficult to think of volcanoes as calm, restricted things, isn't it? But on this scale they are).

The convection current round the hot point is easy; hot air expands, cooler (but not much cooler) air flows in under it, continuous ground level wind blowing inwards, continuous high altitude air flowing outwards, cooling and dropping to maintain the cycle. Calm, smooth and – well, all right, the cycle on Earth is just as regular; hurricanes and tornados are just minor variations. You just got the cycle direction wrong; hot air, being less dense, rises.

What we are in disagreement about is how cold the cold end is going to get.

I think it's going to be easier to measure in degrees absolute than celsius; maybe minus two hundred and fifty, which would freeze out most of the gasses constituting what we think of as "air" in a thin (couple of kilometres, at most) crust. To prevent this I've built a 'wall around the world', ice mountains taller than the atmosphere, frozen out of the cooling cold-travelling air, and ultimately blocking the other gasses from escaping and freezing out. Others see the escaping air carrying enough energy to prevent the far side from getting that cold (think of an Antarctica which never sees the sun at all, and is only warmed by the frigid winds that get that far over already frozen wastes. Air just hasn't the thermal capacity of rock)

But, that close to a star, magnetic lines of force are continuously stirring up the core, transducing tiny fragments of orbital energy into heat. Volcanic heat, geysers, hot springs. Could this be enough to – not take the chill off, but prevent all the carbon dioxide freezing out, at least? 

Calling the region round the hot point a 'storm' is missing the point; it is a trade wind, a reliable airflow, stable and continuous (if the star doesn't flare). It might well have thunder and lightning associated with it, but then it will be a lightning zone, fixed. Storms might (almost certainly will) develop within the airflow, minor instabilities within the greater pattern. further out, in concentric circles, rain will fall, then sleet and finally snow, either renovating my mountains or lost forever on the dark plains strtching towards the cold.


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## Starbeast (Oct 22, 2010)

*The Humans who are run the world, don't seem to change.*

Say we can get to this planet easily and its exceeedingly habitable. 

Governments and big businesses are going to rip apart looking for all of the valuable resources, and will probably treat it like Earth by poisoning it with toxic and radioactive waste from storing it underground. And if there are primitive people there as well, they'll most likely be taken advantage of, especially if the area has excellent soil and/or precious minerals.

Call me a morbid thinker, but governments and big businesses are still doing it today, besides becoming better liars to us common folk.


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## ScrambleEggHead (Oct 22, 2010)

I understand your concerns Starbeast, and that is one likely scenario. There is, however one shining counter-example of this right here on Earth: 

The Antarctic Treaty  was signed in 1959 by twelve countries; to date, forty-six countries  have signed the treaty. The treaty prohibits military activities and  mineral mining, supports scientific research, and protects the  continent's eco-zone. Ongoing experiments are conducted by more than 4,000 scientists of many nationalities and with various research interests.

(Which would also be a good place to study some of the ideas being tossed about in this thread. )

Chris, I may have to point out a possible "faire une faute" about Antarctica. You said "(think of an Antarctica which never sees the sun at all, and is only  warmed by the frigid winds that get that far over already frozen wastes.) 

Quote from Wiki: " During (the southern) summer, more solar radiation reaches the surface during clear days at the South Pole than at the equator because of the 24 hours of sunlight each day at the Pole." 

Also, regarding Antarctica:
The continent has about 90% of the world's ice (and thereby about 70% of the world's fresh water). If all of this ice were melted, sea levels would rise about 60 m (200 ft). 


It is also because of Antarctica that a great deal of the sun's radiation is reflected back out of our atmosphere. If it were not for Antarctica, we would see some very serious "global warming" (for more than one reason). 

Back to the Goldilocks planet, it would seems that not only is the planet in a Goldilocks zone with respect to it's orbit around the red dwarf, but also has a Goldilocks zone on the planet where life (similar to Earthbound life) could exist. I was thinking it might be a good place for "people" like SpongeBob Squarepants to live. (Able to live underwater, and withstand extreme temperature changes, etc.) 

There is one thing Chris pointed out which is also true of our moon. It has to revolve at a constant rate at the specific orbit it's in to keep the same "face" toward the star. This would mean that populations living on the Goldilocks planet in the Goldilocks "ring" would have to constantly migrate to stay in the "zone".


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## chrispenycate (Oct 22, 2010)

They wouldn't need to travel; think if you had a house in Copernicus. You would always be able to radio Earth, which would always be in the near centre of your sky (different bits of it, as Earth is not tidally locked, but always the planet up there. You'd get days and nights, of course, because Earth isn't your source of heat and light; but on our hypothetical Goldilocks body the star is always over the same point, and the twilight zone is always in the same ring; the rotation allows you to stay in the same place, not forces you to move. 

And I don't believe more solar energy hitting the daylight pole than the equator; the radiation (light and the rest) is coming in at such a low angle that a solid degree covers much more surface area than at the equator, where it's effectively straight down, and that's without considering how much more atmosphere it's got to penetrate. The extra hours of low intensity lighting can't compensate for the far more powerful beams round the middle.  

But when I asked you to picture how cold it could get I was saying that Antarctica received quite a lot of sunlight, while this dark side would never have any. And Antarctica can get cold enough to freeze carbon dioxide sometimes, in winter.


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## ScrambleEggHead (Oct 23, 2010)

My sincere apologies Chris - I did not see the word "an" in the sentence: Imagine an Antarctica... My mind read "Imagine Antarctica, which never sees the sun." And I suppose you are right that life would not have to migrate because the planet stays "ahead of the curve", so to speak. It's a bit difficult for me to get my head around these orbital mechanics that are unlike Earth's. But I took the statement about "During (the southern) summer, more solar radiation reaches the surface during clear days at the South Pole than at the equator because of the 24 hours of sunlight each day at the Pole." It is a direct quote from Wiki, although they may be implying a caviat - no cloud cover - at the south pole by using the phrase "on clear days". I suspect there is more cloud cover at the Equator because it is warm and mostly liquid salt water. It is because the 23.5 degree tilt of the Earth is "bottoms out" (toward the sun) during half of the year that this reflection occurs, although I'm sure you knew that.


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