Space 13: How to Have Places to Boldly Go To
(galactic empire continued from here)
About finding planets that will support life
Here's a radical thought: We won't. And we won't want to.
This is the #1 thing people are really getting wrong when it comes to looking for exoplanets to colonize.
All indications are that the basic chemical building blocks of life are actually fairly commonplace. Which means any planet that has free oxygen (this in itself is kind of a red flag because life is pretty much the only way we know of getting large quantities of free oxygen), the right distance from the sun so that we can have bodies of liquid water, also actual water so that we can have bodies of liquid water, .. all of the ideal attributes, will most likely also already have its own life of some sort. It may not be much more than algae or protobacteria, but that won't matter.
Because it will have evolved separately from us it'll be subtly different. They may use a slightly different set of amino acids. They may have their own notion of RNA/DNA where the codings are slightly different.
Which means it's going to screw up our biochemistry something fierce. Their neurotransmitters and enzymes and whatever else will interact with ours in really stupid ways. In fact, the whole place will be this Huge Biohazard for us that we'll need to avoid at all costs (thank you, PZ Myers), and hence useless from any kind of colonization point of view.
Which means if we are looking for Earthlike bodies, we are never going to find the right planet, because even if we find another Earth, we still won't be able to live there.
The only way out of this box will be to build the right planet. Which changes the questions we need to be asking.
About making planets that will support our kind of life
So, we're talking about terraforming, now. Pick a planet, mess with it, try to make it enough like Earth that we'll be able to live there. And I'll say straight off I have no idea what "enough" means in this context; I figure we're going to spend the next n centuries finding out as we try to keep our own planet from changing out from under us.
But once we have some idea what we want, what will matter for candidate selection are the characteristics that are hardest to change, and we already know how at least some of this is going to play out. E.g.,
- Mass/gravity are pretty much set in stone. Literally. There's no way in hell we're going to be able to move enough mass around to change the gravity of a vaguely-earth-sized planet. So this is probably top of the list.
- Axial tilt and orbit shape. Same story. We can probably live with the tilt not being 23°, but too much eccentricity and we'll get unpleasant temperature extremes.
We probably want to stay the hell away from systems with super-Jupiters or multiple stars where the orbits won't be as stable, because having your orbit change out from under you will really suck.
- Distance from the star, we won't care quite so much, because, compared to everything that we'll need to do, putting up mirrors or sunshades will be easy, and that's assuming we can't already get what we need by, say, injecting the right proportions of greenhouse gasses into the atmosphere we're creating to make the place warmer because it's otherwise a little too far out.
It may even be that we'll want to stay away from those dangerous yellow G-type stars, that put out way too much hard radiation, and go for the gentler red ones that are more predictable and last longer. The kind of place where life is more likely to evolve may not necessarily be where we most want to live.
And, interestingly, of the 53 systems that we know about within 15 light-years per wikipedia, nearly all of the red stars are listed as "flare stars", which suggests to me that the only reason we know they're there is because someone saw them flare up, and that the nearby places we'll actually want to colonize are those other 50 nearby systems with red stars that are so well-behaved and dim we still haven't detected them, yet.
Update: These folks say the mass density in our neighborhood is 0.09-0.12 solar masses per cubic parsec, which translates to around 35-45 solar masses in our 15-light-year-radius sphere, but three-fourths of the wiki listing is red dwarfs that are at most 1/2 a sun and can go all the way down to a 1/12 of a sun (Proxima Centauri is about 1/8 of a sun), so I don't think I'm totally off base in imagining there are 100+ star systems here.
We also need to worry about:
- Chemical composition. Yeah. The general problem with planets is they can have pretty much any composition imaginable; planets are made up of whatever was there in the vicinity when they first formed. There appear to be no rules. And there are any number of substances that will be game over for us being able to live there: cyanide, perchlorates, hydrogen sulfide, or any of a thousand other poisons that are actually fairly common but managed not to occur too much on Earth for whatever reason.
whatever rock we pick, we're going to need to core-sample and seismograph it to death to make sure there aren't any hidden pockets of evil too near the surface. We may well have to survey hundreds or thousands of asteroid/planetary bodies before finding one that's even vaguely acceptable.
- Geological activity. It may be like Earth, where all we have to do is stay away from the volcanos and earthquake zones. But it might be a lot worse. Cracks of Doom Everywhere is not something we'll be able to fix.
- Atmosphere is something we can be flexible about. Keep in mind that one earth atmosphere is about 10,000 typical comets, which will be relatively easy to divert, as long as we have a sufficient variety to choose from. Our best bet will be to start from a bare rock that's nothing but vacuum up top, because then we can get exactly the atmosphere we want, it being much easier to add what we want than to remove what we we don't want.
This also means it's not just about finding the right rock(s). We'll also have to track down all the comets we'll need, and if you think about how big our own Oort cloud is, it's a fair bet this is generally going to take a while.
And then we get to combine everything, wait for the dust to settle, introduce our algae, mosses, and whatever else that can spread everywhere, break down rocks and decay into topsoil, plants, all the while seeing what happens with the weather and the climate.
All in all, this is going to be a long term project. I'm guessing thousands of years.
But not to worry, since, by the time we're at the point of starting to do any of this for real anywhere -- hundreds of years from now, minimum, -- we'll already have had plenty of experience with the terraforming of our own planet (we've even gotten started on that already!).
Next: We need to pick up some toys.
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