On Creating Imaginary Worlds: Science Fiction

The planetary considerations here are completely dependent on the size of the stars in question and the the distance between them. Using our own solar system is probably not the best example however though because the stellar distances are not rational; Sol and Jupiter are just too close.

The gravitational issues would not create odd orbits at all. (By odd here, I mean figure 8's and such) The system I'd use is to imagine every planet attached to its star by a string. the string represents gravity. The stronger the pull, the thicker the string. So what happens as each planet orbits its own star in the binary system: you always get a roughly circular orbit. The ellipses are produced by the temporary stronger pull as the planet passes nearer to the second star. So the deviation outside a circle depends on the strength of that 2nd gravitational tug. if the stars are too close-as in the example of sol and Jupiter, the planet gets pulled apart. i think that pretty much covers it.
 
Planet pulled apart? For tidal forces to do that, the stars would have to be very close indeed (I suspect closer than Venus; remember, it's only the difference in resulting forces that tends to desegregate a body; otherwise, you get a vector sum of the attraction of the two (or how ever many) major gravitational attractions operating on every particle in the body. A comet can travel really close to a star (observed) and seems less mechanically well built than a planet; normal, it's had less gravity to squeeze it together. And they don't tend to come apart. The idea of one star pulling on one side of an object, with another the other is very comic book. Gravity is not blocked by intervening layers of matter.

All stable planetary orbits are elliptical, with the – I nearly said primary, but it's of course the centre of gravity of the system; since in the solar system this is within the body of the sun, we have a tendency to think of this as standard, but in multistar systems, this might well not be the case. Actually, considering that some multistar systems do have planets, doing the redefinition of "planet" to exclude Pluto might have been a bit ahead of time; in a binary system with large disparities of mass between the stars should objects orbiting the lesser star be considered as "moons"of it?

So, yes, ellipses. The fact that the solar system's planetary disc was relatively circular, and Jupiter's moon system and Saturn's rings too, does not prove this is necessarily a cosmic rule. A reasonable bet, but don't put the farm on it. Actually, Sol- Jupiter distances can give you perfectly good basic concepts for multistellar setups, particularly if you take Clarke's post-obelisk Jupiter.

There are four stable solutions to the binary star planetary orbits, partly dependent on relative masses of the stars, although one is vanishingly improbable (two stars of similar mass orbiting around their common centre of gravity, with a planet sitting right on the point. I hope it's spinning in the same plane the stars are or timekeeping's going to get a bit complicated). Adding another star, close enough that it's an energy source not just a twinkling point of light that happens to move relative to your fixed starscape makes everything an order of magnitude more complicated, and a quaternary system? Ugh.
 
This question will be a lot easier than the last one. Planets and gravity, is it possible to have an Earth like planet with similiar gravity, but twice or three times bigger? Does a bigger planet always have more gravity?
 
I've seen this discussed before on-site. As I understand it, it depends, at least partly, upon density and mass, rather than just size, so if a planet was larger than Earth, it might have less gravity, compared to size, than Earth if its mass was less per metre cubed.

I could be wrong, but there's also the distance from the centre of gravity involved, I think. I'm still looking for the set of equations to work this out for myself. :)
 
If you cut down the nickel iron core, and built up with silicate rocks, for the same surface gravity you could go up to a bit over one point two times the diameter, that is, one and a half times the surface area, without any major apparent differences on the surface (all right, with less core you might have difficulty maintaining a magnetic field, allowing more charged particles deeper into the atmosphere, so an increased radiation flux, but nothing evident). To go much bigger than this you're going to have to concentrate on lighter elements, and get rid of much of your heavy metal content, and I'm not sure how much of that you can tolerate and remain 'Earth-like'. Saturn, a gas giant, has a surface gravity barely more than Earth's, despite having a hundred times the mass, and a hundred times the surface area, but could hardly be considered as worthwhile real estate.

One way of cheating would to be to shorten the day, to say six hours. The planet would get a major equatorial bulge, so inhabitants there would be further from the centre of mass, and thus lighter, and they would have more lift due to centrifugal force. Still, this is only percentages of reduction, not vast multiples.
 
Clever thinking, Chris but the answer is the bigger the planet density, the flatter we'd be on the surface (until we're squished/or glowing bright green from charged particles).

Abernovo, don't get too bogged down it was just a general question.
 
The higher the density, the higher the mass the greater the surface gravity, yes. Without a radical rethink of the laws of physics, I see no way round that. I was just ashamed at only being able to gain you about half again the planet's surface area. You could manage that just by lowering sea levels, or increasing the percentage of mountains.

Now, if you wanted a smaller planet with the same surface gravity, I could build it round a lump of neutronium thrown of by the collision of two neutron stars, or even a very small black hole.

How about putting a gigatonne or so of neutronium into geostationary orbit, so one point on the equator was at reasonable gravity? Or a Klemperer rosette of six geostationary lumps, so six points were human habitable but you couldn't travel between them, and they were spaced equidistantly round the equator? Robots pulling the telephone lines between the cities, to maintain communications?
 
You don't need much prompting, now do you, Chris?

Just how small could you get and still have earth like gravity. I suspect a small black hole would make it a really small planet. These could be the play things of an advanced race, each having a tiny planet to live on. Now there's a cool idea...
 
If you made it too small; smaller than Switzerland, say, your head would be at a different gravitation from your feet and you'd get tidal effects. And the air pressure would drop off with altitude so fast that weather would be practically in your hat. I'd say make one at least the size of France, if not Brazil. I'm afraid a planet you can walk round in a day, like Saint-Exupéry's Petit Prince has some noticeable practical inconveniences (and not only baobabs) But that's where the limitations lie; even restricted to neutronium, without the use of black holes, you could get the necessary gravitational field with something the size of Manhattan. Assuming, of course, you could get the neutronium.
 
How common do we think (intelligent) life is?

It seems everywhere we go in space organic compounds have been found. This could just be our local area of space and it could be life from Earth infecting local space but I find that unlikely. The only other conclusion is that space is full of these organic compounds. That being the case the seeds of life must be everywhere.

Now galaxies are densely packed at the centre and that for the majority of planets in any galaxy, life will be zapped to a radioactive sludge before it has a chance to start by close proximity to all these suns. However, not all planets are going to be in this densely pack region of the galaxy, which is usually the core/centre of the galaxy. Oddly enough, Earth is not in the centre of the galaxy and we’re way out on the edge on a spiral arm. I’m going to plant my flag and say life would normally develop in the safer edges of a galaxy, well away from the very nasty cosmic radiation.

That still leaves quite a lot of material knocking around for life to get going on. The assumption that we’d be able to spot other intelligent life has lots of problems with it. We’ve only really been looking for life in the last 100 years or so, you could change that number, it’s not that important. Human life has existed, us the Homo Sapiens, for around 250k years, with 50k years for human culture. Our technology has only evolved to the point where we can peer into the depths of space with some understanding in the last 100 years or so. If a human from today went back in time just 2,000 years ago, landing in a jet plane and jumping out to say hello to the Romans they’d have thought us gods. So yes, we are looking into the depths of space, but do we know what we should be looking for?

So I think life will be falling out of the trees all over, with every 20th to 50th sun (away from the galaxy core of course) having a planet with life. Intelligent life will be there as well, but we have to assume intelligent life is a quirk of nature, as life has been on earth for eon’s and it’s just been us so far. So evolution it would seem does not like big brains or we’d have furry neighbours eating banana’s fighting with the lizard next door over the state of their lawns. This has not happened, it’s just us I’m glad to say. So, planting my flag again, there will be lots of life out there but intelligent life will be rare.

How rare, who knows?
 
I've read several articles that speculate, life on other planets "may not be that rare." Yesterday, I read, that with the new endeavor to find solar systems, with habitable planets, they have found two things.
1) Evidence for a super Earth-size planet, in the habitable zone of a star 42 light-years away in the southern-hemisphere constellation Pictor.
http://www.alaskadispatch.com/article/astronomers-spot-huge-earth-planet-may-sustain-life
That is in our proverbial back yard.
2) That Stars with planets are more common than not. It is a matter of whether some planets are in the right zone, (distance from the sun,) to have water in a liquid form.
 
I think they'll be lots of planets with life, 1 in 50, or less suns is my bet. So lots of places for us to go with plenty of elbow room - well, for us, the native life may have to go... We're just starting to turn the rocks over, Stephen, who knows what we'll find out there?

Actual intelligent life, self aware beings, there are plenty in my WIPs but how many are actually out there?
 
There is no particular reason why life should be restricted to planetary surfaces; moons, asteroids, atmospheres even comets might seem unlikely spots for life to be generated, but once it exists, there's no reason why it can't colonise them.

On the other hand, there is no way of giving a probability of life developing anywhere, or surviving in a particular environment, until we have a wider database to base judgement.

Then there is the problem that our present definition of 'life' is totally dependent on our experience of life in one planetary environment. Which might be perfectly adequate (defining the difference between a jellyfish and a chemical synthesis plant) but might equally be completely wrong in a slightly wider view of the universe.

We need to find viable, non-terrestrial-origin life before we can start even guessing how widespread the self-regenerating phenomenon is, and need to recognise it before classifying it. From where we now stand any absolute statement is based on faith, not knowledge.
 
I'd say intelligent life would be rare, the product of particular stresses (like rapid ecological change). It takes a lot to develop big brains (and as Carl Sagan noted, our brains evolved so fast that it outmatched our poor mothers' pelvises). Live birth only causes pain in humans, and I'm not willing to put that up to punishing Eve for the apple.

If intelligent life is rare, I am disposed to having more than one intelligent species evolve on a nice, biodiverse planet like Earth.
 
Even if intelligent life is only one in every thousand stars and once every billion years, with 300 billion stars in the Milky Way and 13.2 billion years old - I need a calculator, but I think it's a lot.

I'm fairly sure it would be a lot!

But would we ever meet them, our alien neighbours?

We could have histories that missed each other by a piddling million years, and never know. In my WIP's I have lots of aliens, but for us I think we are a spark flaring up in a dark sky. Yet it would be nice if we did meet our neighbours, but very unlikely I think.
 
Hey guys, I got a silicon based alien beings on a work in progress book I'm writing. I got a question about its potential resistance to radiation. They're humanoid forms, but I dont know if it is really credible since they live really closely to a sun. I'll not describe them on here, but I'd like to know how you imagine them and what physiological characteristics would you incorporate on them.
 
I don’t think a silicon based life form would look just like us. Even on earth, there is nothing that looks just like us so why would an alien end up looking like us?

I would give them eyes, ears, touch etc. and all the other senses they’d need to move about in an open environment. Evolutionary convergence for eyes has happened many times here on earth, so why not the same for your alien life. Just consider the environment they’d live in and what changes that would force their bodies into.

I’m not sure about the radiation question, hopefully others will come along and help as I think it’s a good question. Yet for replication of DNA or alien silicon DNA I don’t think any disturbing radiation would be a good thing.
 
Galaxy may have 11 billion Earth-like planets - SFGate

A double post by me - see post above on the number of earth like planets.

Ok, there are 300 billion stars out there, such a small number.
Possibly, 11 billion suns with earth like planets, see link above.
Thats 3.66% red dwarf stars systems with the right conditions for life.

Ok, there are 300 billion stars out there, such a small number.
Possibly, 40 billion red dwarf suns with earth like planets, see link above.
Thats 13.33% of stars systems could be just like ours.

Or a total of 17% of star systems could have earth like planets with the right conditions for life. That's a much bigger % than I would have pumped for - I'm excited in a nerdy sort of way, and I'm not that nerdy.

Clearly all guess work, but even still.
 
For the silicon-based lifeform.

If something has evolved somewhere it will be adapted to that somewhere. If there is a high radiation flux it will tolerate, or indeed require a lot of radiation, just because, throwing the dice, anything which didn't tolerate lots of rems died, and left the field open for the ones that did. It might require more backup copies than DNA, or tougher triplicated or quadrupled data storage, but it will absorb the radiation with a mutation percentage in the same order of magnitude as Earth. Use the argument of 'intelligent design' you get the same argument, just a tad less diversity.

Humanoid? If you like. We know that system functions. Vision would work differently, but that shouldn't matter until we start comparing colours with them. I doubt whether the pentadactyl limb would carry across, so number base would be different, but symmetry is high probability, and four limbs a decent risk (though six or eight would be more interesting – no, all right, you want humanoid).

Having 'Earth type' planets neither guarantees life will develop, nor that, if it does, that it will evolve in a similar fashion. With only one point on a curve, making any predictions is – well, it could be considered as 'unwise', if it weren't that further evidence was unlikely to come to light before the claim had been forgotten. Basically, until we have actually been to another world there is no way to say if life is a common phenomenon, or extremely rare; all the computer models in the world can't replace a single experiment. With only estimated data, I don't care what the optimism or pessimism of the calculations, we can't know.

If a remote spectrogram of an extra solar planet shows an unstable gas mix – like methane and free oxygen in Earth's atmosphere – the hypothesis of life having risen independently is strengthened, but even then it's not proved. But that will require telescopes with a precision far higher than we have now – not impossible but I doubt it in my lifetime.
 
Life is nothing if not cheap. Dust from a cave that has been sealed for 20,000 yrs. will immediately start making little mutating lifeforms by just adding water. The Galaxy is bound to be swarming with every type of creature, probably weirder than science fiction. )
 
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