Hatrack River Writers Workshop: Can I have two habitable planets the same system?

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Posted by skadder (Member # 6757) on :

Simple question. I want two habitable planets in the same system. One needs to human habitable (liquid water etc.) the other could push it a little with regard arid desert feel. but ideally they would have a similar feel.

I was thinking about two planet size moons circling a massive gas giant--although what would that do to seasons, day/night etc?

Any thoughts?

Posted by Rhaythe (Member # 7857) on :

The dark cycle for those planets when they enter the gas giant's shadow would be problematic. That would likely throw local climates for a whirl as the planet plunges into the cold dark of space.

Another option would be two temperate planets orbiting one another. Both can stay within the temperate orbit range of the parent star and would function with similar tidal behaviour as the earth and the moon. Downside to this scenario is that, after a length of time, both planets would be tidally locked and would only show one face to one another, but that takes a long time.

If this isn't your cup of tea, a planet in an opposite orbit of earth (on the other side of the planet) can be gravitationally locked so as to avoid one another. They would never have line of sight, but they could easily exist. Check out information on Antichthon, or Counter-Earth, for ancient theory on this.

Posted by MartinV (Member # 5512) on :

You can do what Ursula le Guin did in her novel Dispossessed. There is a planet and its moon but the moon is big as the planet itself, making it a twin system. The planet Urras is rich and fertile, while Anarres is a poor, desert place.

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

[This message has been edited by MartinV (edited January 03, 2010).]

Posted by extrinsic (Member # 8019) on :

The Earth and Moon are a binary planetary system. By current scientific definition a terrestrial planet and a planetesimal, though popular opinion regards the Moon as a satellite of Earth.

Two bodies of approximately similar mass with different compositions and rotations could conceivably orbit a primary star in a braided path. One basaltic crust and small metalic core, the other granitic crust and large metalic core. Either, both, or neither could be barren, oceanic, terrestrial, arid, or riverine. Combined mass of a system of habitable planets would put it farther out from a star of Sol equivalent mass, closer for a slightly more massive class G2V star. A critical factor is that the planets generate strong tidal forces. Life can thrive where tides aid in flushing away wastes and toxins in stationary life.

Rigel Kentaraurus A (GV2) is a suitable fiction candidate at 1.2 Solar radiuses and 1.52 times as luminous as the Sun, roughly 4.5 light years from Earth. Currently, no extrasolar planets have been identified at Rigel A or B. B is a mere 33 AU from A, and has a luminosity of .446 the Sun's.

Posted by Teraen (Member # 8612) on :

Another option is to have a two star system. One star is the big one in the center, and one planet orbits at an earth-like distance from that.

Billions of miles away, a smaller star orbits (like uranus-orbit or farther). Its a red dwarf, so it doesn't affect planet 1 very much. Planet two orbits that one, and since it a red dwarf, the habitable zone is only about 0.1 AU from the planet, so it could stay in orbit without getting diverted by the rest of the solar system. And, its far enough away from star 1 that it doesn't affect the climate as much (though, since the center star must be larger, that star would have a greater affect on planet 2's climate than the red dwarf on planet 1's climate. But not enough to be significant. Even uranus is pretty cold...)

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

Posted by Matt.Simpson01 (Member # 8937) on :

Here's one thought. Most scifi is something that we think is possible, but we don't have what is in the stories because it hasn't been invented yet or the technological know how is beyond our current capabilities. The perfect example is FTL travel through space. There are so many different names just for that one technology, and most of them are believable to a certain extent. The most well known is probably the warp drive that ships in the Star Trek universe use. If you follow that storyline, it was developed by a drunk just trying to survive after the third world war on earth. There are plenty of things that we cannot explain even with what we know today. Heck, a hundred years ago, the computer was something that was only found in science fiction stories of the day.

Given what we know about our own solar system, there could be two moons of a gas giant like jupiter or saturn that are both inhabitable and inhabited by different species. It wouldn't be hard to justify something like that when it to having two planets. Also, the simpler the better. It would detract from your story if you had to explain too much about how the two habitable worlds came to be in one solar system.

Posted by Phobos (Member # 8883) on :

I have this nagging self characteristic that I cannot really write something unless I believe that is possible. I know, not a great problem to have when you write speculative fiction. But what it boils down to is that I have to do tons of research on many subject, especially atronomy when writing. Planet building is the most difficult and consuming. I have spent hundreds of hours studying; tidal resonance, orbit patterns, hyperbola, etc... I have to convince myself that the planet I created could potentially be out there somewhere.

What I have found is, a habitable planet is not very likely to be entirely desert. Having the amount of water and oxygen nescessary for supporting human life, combined with temperature differential, rotational patterns, etc...pretty much ensures that there will be weather patterns and variations in ecosystem at varying geographic locations. There is more potential for a planet to be a polar desert simply for the fact that if the planet remained cold enough to always be frozen, there would be less weather patterns, even though there would be some because there would still be variances in temperatures across the planet.

But having two habitable planets in the same system is not unfeasable by any means. I am still not convince that our system doesn't have two habitable systems. Perhaps not by humans but some other life

I like the idea of moons supporting life, especially as you mentioned against a gas giant. If the moon wasn't captured in orbit by the planet, lets say it was hurled and collided with the planet it now orbits there is huge potential for the mixture of similar elements on the moon or moons. They could be very similar in composition and are obviously in the same orbit and therebye recieve the same amount of radiation from there star.

Any way I am just rambling now. I need to go to sleep. I hope this helps.

Posted by Andrew_McGown (Member # 8732) on :

EDIT:
I changed my comment and that meant some of the following ones did not read properly.

Mine was about whether it is more a question of habitable zones or alternative heat sources.

Does a bigger star have a bigger habitable zone and if so why not dozens of habitable planets?

What is the biggest star theoretically possible?

Sorry to have changed it, will do it in subsequent posts in future.

Andre

[This message has been edited by Andrew_McGown (edited January 04, 2010).]

Posted by rstegman (Member # 3233) on :

They discuss a range of orbital distance that life can survive. If one is at the inner edge and the range, and the other is at the outer edge of that range, then it would not be hard to have two habitable planets.

Hotter the star is, the wider that area is, but the shorter the life span of the star. Also, as the star gets hotter, one starts dealing with higher levels of radiation.

desert and non-desert, strictly depends on how much water the planet has.

Also the arrangement of the continents to that water will have a big effect on whether the land is arid or not. The seas near the poles will have a different effect than having land near the poles and the water around the equator.

Keep in mind the nature of the winds, at least here on Earth. The air rises at the equator, dropping lots of rain. it then comes down at the tropic of cancer and capercorn. Is dry. It then goes to about mid way to the poles and rises again, dropping the moisture, then comes back down at the poles, dry again.
All you have to do is to have the main land mases in the dry air areas and you have deserts.

Also note that the north pole has water, and the surrounding land masses are temperate. The south pole has land, and the surrounding land masses are a whole lot cooler.

Balancing the amount of water, placement of the water, and where the planet is orbiting the star, will get the effect you are after.

Posted by shimiqua (Member # 7760) on :

What I think is interesting is if both planets have life, can they see each other?

If the two planets are as close to one another as our moon is to us, maybe they could see a bonfire, or electricity when they develop that. The question is, if they really know another form of life is out there, how would they react? How long would it take them to find a way to visit each other, and what weapons would they bring with them?

I think they would be watching each other closely, not knowing if they were enemies or friends. Maybe one could make a giant message that the other could read, a huge project, interstellar communication from building a wall into a peace sign, or something.

Plenty of ideas in this one. I approve.
~Sheena

Posted by Rhaythe (Member # 7857) on :

Once a civilization advances far enough to have cities, then life on the opposite world would certainly be able to see the nighttime glow of city lamps on a clear night:

http://science.nasa.gov/headlines/images/lights/earth_lights.jpg

Posted by Teraen (Member # 8612) on :

One more thing: given the randomness of evolution, it is unlikely to the point of virtually impossible for two planets to evolve intelligent life capable of getting to the other planet simultaneously. Consider that we've had space travel for less than one hundred years, and modern science for only a bit longer than that. Humans have only been around for a fraction of life on Earth, even in our less than advanced technology state. And life has existed for billions of years. Imagine if the asteroid had never kicked off the dinosaurs. Or if the ancient Romans had figured out a steam engine. Different outcomes of a million random events would have changed human history.

If you have colonists (most likely scenario) from one world, or both planets were colonized, or maybe one society is advanced enough to travel by space and the other is still caveman society (less likely), then that fixes this little inconvenience.

Posted by Lionhunter (Member # 8766) on :

quote:

What I think is interesting is if both planets have life, can they see each other?
If the two planets are as close to one another as our moon is to us, maybe they could see a bonfire, or electricity when they develop that. The question is, if they really know another form of life is out there, how would they react? How long would it take them to find a way to visit each other, and what weapons would they bring with them?
I think they would be watching each other closely, not knowing if they were enemies or friends. Maybe one could make a giant message that the other could read, a huge project, interstellar communication from building a wall into a peace sign, or something.
Plenty of ideas in this one. I approve.
~Sheena

THAT is very interesting. Very interesting idea. Ya ya.

Posted by shimiqua (Member # 7760) on :

quote:
One more thing: given the randomness of evolution, it is unlikely to the point of virtually impossible for two planets to evolve intelligent life capable of getting to the other planet simultaneously

Unless they were once the same planet and it was split in two by a meteor, or something, and an early form of life now inhabitants both planets. Now these two moons circle each other, probably tidally locked.

Another random idea. A tower of babel trying to reach the other planet.

Interesting.

Posted by Brad R Torgersen (Member # 8211) on :

If Mars was more massive, it could have been our Other Earth in our very own solar system. Alas, its gravity is too weak to keep a firm grasp on all those oxygen and nitrogen molecules.

Sol's theoretical "safe zone" isn't as narrow as we might imagine. I think it begins somewhere inside the orbit of Venus and ends somewhere near the asteroid belt. Lots of room in there for speculation and extrapolation.

One thing that might be interesting: an Earth-sized, clement world on an extreme elliptical orbit, which approaches very near its star during some years, and is yet very far away much of the rest of the time.

I am sure plenty of authors have already exploited that model, I just haven't read the stories yet.

Posted by snapper (Member # 7299) on :

I believe the reason Mars has lost much of its atmosphere (theory, not a definite fact) is it lacks a strong magnetic field. The solar wind sweeps bits of atmosphere away without one.

Also, as far as the gas giant question goes...

I think Jupiter emits more heat than it receives from the sun. You could create a system where a gas giant emits enough to warm its sattelites. That way moons with orbits varying a half million miles could have different climates and not be too affected by the ecillpses from the large planet.

Posted by Edward Douglas (Member # 8872) on :

Simple questions rarely get simple answers, so I apologize in advance. Here's my contribution. When considering habitable zones for the stars within my galactic milieu I have accepted the following assumptions:

1) That any habitable planet orbits only a main sequence star.

2) That that main sequence star cannot be part of a binary system. The tidal forces on a planet affected by two suns would be enormous.

3) A low mass star is unlikely to have the gravity needed to trap comets and asteroids that deposit the building blocks of life onto a planet via collision.

4) A high mass star has more than likely already burned past its habitable zone (so long as I measure that zone from the core of the star and not the perimeter).

Theories abound, but most suggest that life evolves only on planets that orbit main sequence stars that are not part of a binary system and are strong enough to trap and keep a band of comets in play. A habitable planet must reside within that star's habitable zone (usually .75 to 1.5 AU). In our system Venus lies at .72AU from the sun and Mars at 1.52AU from the sun, putting both just beyond the habitable zone of Sol.

Once I've established these "rules" then I have to place that planet around a main sequence star and put that star somewhere in my galaxy. Life is more likely to survive and flourish the further it is from the galactic core (the outer arms of a galaxy most likely). The gamma radiation associated with proximity to the galactic core would never let life get off the ground.

Of course, even with "my rules" there will be exceptions. Rogue planets supporting life by surviving off the life giving elements within gaseous clouds. Earth-like planets that are "adopted" by Jupiter-like planets as a main sequence star begins to expand. Much is possible in the imagination if I can make it make sense.

Concerning your human habitable versus desert-like planets: I don't think a planet will be all one or all the other. Even a "water world" would have thick ice layers at its poles. While I accept that a planet can be as hostile as a desert and support life that would be because that too would have cold climbs at the poles and at the higher elevations where life would be most likely to evolve and thrive. So, when considering the actual habitability of a planet, the geography of that planet will play a larger role, I think, then where in the habitable zone that planet resides.

Hope I've helped.

Posted by extrinsic (Member # 8019) on :

Mars is actually a planet beset by global warming gas, 96% carbon dioxide composition, 187 K, -87 C, -123 F, as is Venus, 97% carbon dioxide, a toasty 735 K, 462 C, 864 F, and Saturn's Titan satellite, 98% nitrogen, but it's the methane, 1.6%, that mostly causes its global warming to a frigid but habitable 93.7 K, -180 C, -291 F, close to the Moon's equatorial minimum (nightside), not to mention Titan's trace hydrogen cyanide fraction.

Posted by dougsguitar on :

I think it would be interesting to see their technological developments to counter the problems of survival rather than inventing a planetary system of environmental balance... maybe they were space travelers who encountered something that made a few ships crashland on one planet while others crashed on the other. The story could cover their final attempt to re-connect, overcoming the elements... or something... kinda rambling along here... somebody please take the mic...

Posted by Edward Douglas (Member # 8872) on :

Oops! Maybe I misunderstood the question. I was approaching it from the viewpoint of a world developing life, and not from the view of an advanced civilization making a planet habitable. In terms of the latter, then anything goes really, but, as doug suggests, then you have to explain (and make believable) the technologies used to "terraform" a world.

Your advanced civilization won't be restricted to a star's habitable zone at all if they are able to introduce the elements necessary to sustain life as they know it. But then come the ethical questions, which usually separate the good guys from the galactic bad guys: what do you do if some sort of life-form already exists on a planet you want to make habitable for your own kind?

Posted by philocinemas (Member # 8108) on :

quote:
One more thing: given the randomness of evolution, it is unlikely to the point of virtually impossible for two planets to evolve intelligent life capable of getting to the other planet simultaneously. Consider that we've had space travel for less than one hundred years, and modern science for only a bit longer than that. Humans have only been around for a fraction of life on Earth, even in our less than advanced technology state.

There is a binary planet system described in Spock's World, IMO one of the best Star Trek novels ever written, where the two planets, Vulcan and Romulus, were similar to our Earth and moon. Vulan develops intelligent life and Romulus develops lower forms of life with a similar atmosphere.

In the novel, it is the knowledge of life on Romulus that drives Vulcan to develop space flight earlier in their civilization than what Earth has experienced. They become a technological society, while still being slightly barbaric.

Later, Vulcan develops a philosophy of total self-control and intellect, while the colonizers of Romulus become a war-faring culture. This isn't what is reflected on TV and the movies, but it was a very interesting take on how knowledge of extraterrestial life would affect intelligent lifeforms during the development of civilization.

Posted by Lionhunter (Member # 8766) on :

quote:

There is a binary planet system described in Spock's World, IMO one of the best Star Trek novels ever written, where the two planets, Vulcan and Romulus, were similar to our Earth and moon. Vulan develops intelligent life and Romulus develops lower forms of life with a similar atmosphere.
In the novel, it is the knowledge of life on Romulus that drives Vulcan to develop space flight earlier in their civilization than what Earth has experienced. They become a technological society, while still being slightly barbaric.
Later, Vulcan develops a philosophy of total self-control and intellect, while the colonizers of Romulus become a war-faring culture. This isn't what is reflected on TV and the movies, but it was a very interesting take on how knowledge of extraterrestial life would affect intelligent lifeforms during the development of civilization.

Didn't read the novel, but wasn't Romulus the homeworld of Romulans? So Vulcans had a satellite named Romulus, and then the Vulcans who left Vulcan so that they wouldn't conform to the whole logical thinking named their new world after their former moon?

edit h,should have read till the end:P

[This message has been edited by Lionhunter (edited January 09, 2010).]

Posted by Brendan (Member # 6044) on :

quote:
One thing that might be interesting: an Earth-sized, clement world on an extreme elliptical orbit, which approaches very near its star during some years, and is yet very far away much of the rest of the time.
I am sure plenty of authors have already exploited that model, I just haven't read the stories yet.

You are correct. Two famous ones

A Deepness in the Sky - Vernor Vinge (2000 Hugo Award winner)

Helliconia Trilogy - Brian Aldiss (1982,1984 BASF winner, 1983 BASF nominee, 1982, 1984 Nebula Award nominee, 1982 Campbell Award Winner)

Posted by Tricia V (Member # 6324) on :

The 'verse of Firefly is a system with dozens of planets and hundreds of moons, though there is a supposed terraforming tech to explain it. It did bug me a bit, what about day lengths and seasonal differences, when every planet seems to be more or less central california. But Nathan Fillion is hot enough I don't worry about it. So, yeah, your story just has to be greater than or equal to Nathan Fillion in hotness and the science doesn't matter.

Posted by Architectus (Member # 8809) on :

For my sixth novel, I've decided to have two main space stations orbiting a dead planet, or least dead enough that living on it is hard. The two main space station have several linked stations to make up a huge nation. Demi nation and Heroc nation.

So you could do that, or you could have one of the planets be artifical, or a moon converted into a living place with shielding and air bubbles etc.

Or you could do what others have said.

Posted by Brad R Torgersen (Member # 8211) on :

I've read "A Deepness In The Sky" by Vinge, and enjoyed it very much.

I'll have to go back and check, but I thought the Spider planet had a star that flared and died periodically, not that the planet was on an extreme orbit?