01 September 2011

Imagining Space

I have been a reader of science fiction, on and off, most of my life, although in recent years; well, decades, I have mostly found the field pretty devoid of anything much worth reading. Anyway, there's always been a subgenre, dominated by writers who took some care with astronomical detail and tried to make their space fiction plausible, at least within some conventions, such as "hyperdrive," to get around the fact that stars in the Galaxy are so far apart that travel to them even at relativistic speeds is effectively impracticable (that is even assuming that relativistic speeds were technologically feasible, not only in terms of energetics, but in terms of survivability... anything moving at that speed is essentially hard radiation). Probably the first classic example of this kind of so-called "hard" science fiction is Mission of Gravity (1953) by Hal Clement; a much praised but not too often actually read book.

It's a spectrum, really. Writers like Poul Anderson and Larry Niven, or even C. J. Cherryh and Ursula LeGuin, attend to detail: they set their stories in the real Galaxy, and mention real stars, and talk about such things as the stars' spectral classes and the orbital peculiarities of planets (such as tidal lock, i.e. the same face always to the star (not a convenient or possibly even survivable condition, but probably pretty common; think of the moon); or seasons caused by orbital eccentricity rather than axial tilt; that sort of thing). People who love to imagine what other stars and their worlds might actually be like loved this sort of thing, although eventually it pales; the contrivedness of it all becomes too glaring. Some writers, like Jack Vance and Iain Banks, set their stories in space, posit magical technology allowing space travel to be a lot like maritime or air travel on Earth, and get on with their (very different) baroque story telling. Frank Herbert imagined a vast span of time and space, including mention of some real stars, but his imagination went more towards imagining strange evolution of man and how history would be affected by it: Dune is incomparable, but most people would agree that after that, the whole thing just kind of gets out of hand.

More recent writers sometimes pay a lot of attention to scientific plausibility (Stephen Baxter comes to mind), but for my money, few "space fiction" writers still active can tell a story that holds my interest. Iain Banks is one.

Still, even today, almost all of this space fiction is based on a mindset that thinks "stars like the sun" are going to be more or less just like the sun. There will be watery worlds more or less like the Earth. The pattern of the Solar System: rocky inner worlds, gas giant outer worlds, stable, long lived star, which has somehow maintained a stable set of conditions on Earth for hundreds of millions of years, long enough for us to evolve, etc., all will be the rule. This kind of begs the issue, what is the actual truth, as now understood? It used to be that not much was actually known, or at least widely published, to indicate otherwise: one yellow dwarf star was assumed to be much like another.

But, it's really quite interesting. If you follow extrasolar planet research, or, for that matter, just read what's readily available from studies of stars themselves, you'll realize that these assumptions are not justified, at all. Look at this article about just one nearby "sunlike" star, 61 Virginis, in Wikipedia, to see what kind of detailed information is currently available. There are literally thousands of such articles available. 

Stars vary enormously. More than half of star systems have more than one star. Often in close orbits, which probably rule out planets in orbits where water could remain liquid. Stars rich in metals (Astronomese for everything beyond Helium on the periodic table), seem to be more likely to have planets; and it's already becoming apparent that at least some dwarf stars don't have planets, although why they don't isn't really understood. It used to be thought that older stars, that formed early in the history of the universe, were always metal poor, and more recent ones were metal rich; and while this pattern may generally hold, there are exceptions. The Sun is moderately metal rich, even for its age, but some even older stars (a nearby example being 16 Cygni), are even more metal rich, so the relationship between age and metal content is not regular or simple. Planets, it's now known, do not typically form in the Solar System pattern. Gas giants are often found in inner orbits. Nor are the nearly circular orbits of the Solar System's planets typical. Many systems have apparently stable but nonetheless highly eccentric orbits. Moreover, stars, even when similar in many respects to the Sun, are all different. 18 Scorpii (along with HD 98618 and HIP 56948) are thought to be "near solar twins," but even these stars have differences that might be critical, and might cause a planetary environment in their vicinity to be unstable. Further, there is current speculation that just maybe the dimmer, cooler, orange dwarfs (late type G and early type K), which live longer than brighter stars like the Sun and may settle into stable temperature ranges for longer periods, may be more "life friendly" than stars resembling the Sun (which would be a good thing, since something like 1 in 15 stars is main sequence type G5 thru K5, while stars from say F8 through G4 (the sun is usually given as G2), may only be about 1 in 30. *

So, what? I have no answers. Science fiction has become tired; it no longer seems to explore the edge of possibility. The universe is, clearly, quite a bit more varied than we thought. Is it full of life? Other civilizations? Other worlds like our own? We still don't know, but one thing is pretty clear: not just like our own. What is out there is as varied as the variation of landscapes on Earth, and the life that may have evolved will be varied too. Somehow the innate curiosity of human beings is outer-directed: someday we will know these things, if we survive; in the meantime, we need a bit better imagination to conceive of their possibilities.

* By far the majority of stars are tiny red dwarfs. Stellar population is more or less in inverse proportion to mass. Red dwarfs don't produce the kind of light in abundance that's probably necessary for terrestrial type life, and they have such narrow zones where temperatures could be right, which, in turn, are so close to the stars themselves, that the planets would usually be tidally locked, one face always to the star. This causes obvious problems, greatly accentuated by the fact that almost all red dwarfs flare, i.e., are quite irregular in their output and occasionally would blast their close in planets with excessive radiation. Thus, despite being so dim that almost none of them are close enough to even be visible in the night sky, these little stars, which make up something like 85% of all stars, aren't very good candidates for having living worlds as companions.

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