So I promised, a while back, a two-part post about astronomy and sci-fi. I’m finally following through on that promise!
This post is — finally! — the first part of that “series.”
Now, as I’ve mentioned before, I am an astronomy nerd. Hell, I just bought a couple of new college textbooks solely because my old ones are getting somewhat out-of-date. By the way, if you want a little light reading before bedtime, hit the chapter on the Hertzsprung-Russell diagram. You should probably leave the excitement of the section about dark energy for some afternoon reading, however…
Anyway, I wanted to tackle a bit of “Our Place in the Universe” before I got into the second post, the one about how I try to include that in my sci-fi writing.
First off, a bit of background that I’ll call the “Nothin’ Special Principle.” Most astronomers hold and adhere to the idea that neither the Earth, nor the Solar system itself, is special in any way. They look at our little neighborhood as completely “average,” and build theories and assumptions from that starting point.
The problem is, that principle is looking less and less true. There are a number of “special” things about our system, and about Earth itself. Now, before I list those things, there is the one big thought/question that comes to mind: are we here because of those “special” things, or in spite of them? The answer to that one is out of my paygrade, by the way…
Okay, so to the “specialness” that kinda, sorta sets us apart…
First off, it’s the age of our Sun. In order to have complex life — let alone intelligence and development — you have to have metals*, and a lot of them. You have to have things like carbon and oxygen and iron and copper and potassium and the all the other crap we take for granted. Hell, even before we got around to using those metals to make tools, we had to have them as integral parts of our biology. And the only way in the universe you get elements heavier than hydrogen and helium is through the life cycles of large stars (birth – rapid growth – death by supernova).
*A quick explanation: words in astronomy are generally different than they are in chemistry or, indeed, in real life. In astronomy, any element heavier than helium is a “metal”.
Our Sun is either a 4th or 5th generation star (thoughts and opinions differ on precisely which). That’s pretty normal, by the way, for a mid-sized, main sequence star. But, the simple fact is that we as a species needed those previous generations of stars in order to have the planet and solar system that we call home. No first generation star still exists (long, different story on that), and the 2nd-3rd generation ones that are still around just don’t show the metals required for life.
The important deduction from that is that any star that is able to support the development and evolution of life has to be around the same generation star as our own in order to have a sufficient level of “metallicity.” Now, our Sun is currently about 4.5 billion years old — pretty much middle-aged for it’s size, generation and composition — and the Earth is something like 4 billion. If we guess that similar stars/planets are about the same, or younger, that would put any intelligent aliens in another system at about the same level of development as us (give or take a few millennia). We might, when you get right down to it, be the first — or among the first — example of intelligent life in the entire galaxy…or even the entire universe.
Okay, so that’s the “specialness” of the Sun. What about our solar system itself? We used to think it was pretty much normal and average….then we started discovering planets and systems around other stars. The more planetary systems we find, the more we understand that there really ain’t no such thing as “normal.” In fact, our system is looking more and more like an unusual outlier than the norm.
Four billion years ago, when the Earth still had that new-planet smell, the solar system was a very different place. Most of the planets’ orbits were different, and there were something like 4-5 times as many planets and bodies running around. It was also a shooting-gallery, with all those bodies smacking into each other on a regular basis.
Why does that matter?
Two reasons: the gas giants, and Earth itself. Jupiter and Saturn were, back then, in resonant, mutually supporting orbits that kept either of them from migrating closer to the Sun through the inner solar system and, well, screwing everything else up. Those two also “adjusted” the orbits of the other planets into the stability we see today, along with either eating or ejecting from the solar system an awful lot of “extra” bodies.
As for the Earth itself…well…one very specific part of that shooting gallery made all the difference. The Earth, Mars and Venus really aren’t all that different, when you get right down to it. Similar sizes, similar compositions, and roughly similar orbits. So why is Venus a hellscape, and Mars cold and dead, while the Earth is what it is? Why is the iron core of the Earth almost twice as big (in relation to overall planet size) as the cores of the other two? Why do we have a moon that is almost a quarter of our own size, when they have none (Mars’ two tiny captured asteroids don’t really count). Why?
Because we got smacked.
We got smacked hard….and it made all the difference.
Not too long after the Earth formed, another planet — about the same size as Mars — hit us. Now, getting hit by another planet would usually be considered a “bad thing,” but this one hit us just right. It hit at an angle shallow enough that it didn’t just shatter the shit out everything, but deep enough to merge the two bodies together…and to create our helpfully large moon in the process.
The real key to that merger is that the Earth kept the other planet’s core, in addition to our own. That “second” core gave us a natural magnetic field that is much stronger than we “should” have. That stronger field is why we still have an atmosphere, where Mars has almost none remaining (about 1% of ours). No extra-large core, and very, very likely there is no life on Earth bigger than bacteria…if we even got that much.
And the water we have… Oh, the water… We have too much. Okay, so it’s not really all that much, not when compared with places like Ganymede and Europa, but it should have all boiled away while the sun was still an angry teenager and flaring like mad. It probably did boil away, in fact, but we got more…and no one is sure how. Asteroids and comets, most likely, but no one really agrees on any one mechanism for that.
So, it all worked out for the best in the end, but do you have any idea of the odds against all that working out? The right amount of metal…two gas giants not doing what most of the other giants we can see have done…a collision that added rather than destroyed…oceans and lakes for swimming and boating and, oh yeah, growing life…
We beat the odds as a species — and that’s pretty damned cool — but there is just no way in hell you can argue that we are average. We kinda need to consider the possibility that Our Place in the Universe, or at least Our Place in the Milky Way, comes down to one word: alone. We might be it, we might be all there is when it comes to intelligent life.
That thought is depressing as hell.
Okay, okay…if you want a bit of hope that the entire freaking Universe is NOT culminating in Trump, Pelosi and the Kardashians, here it is: there are something like 300-400 BILLION stars in our galaxy, and something like 300-400 BILLION galaxies in the observable universe. That is roughly an astronomical shit-ton of stars. Out of all those stars, there has to be at least one that also beat the odds!