Nova remnant in the Z Camelopardalis double star system. Image courtesy of NASA/JPL-Caltech.
One of the top-ten all time great Sci-Fi books on almost any list is Isaac Asimov’s Foundation Trilogy. As a story it is superb. As science, well…
Asimov has swarms of humanity living in star-crowded regions of space where, to put it mildly, earth-like planets, and therefore life, would be highly unlikely. While reading (and re-reading) the Foundation series, the thought of excess radiation in galactic centers used to gnaw at the back of my mind, making it hard for me to suspend disbelief as completely as I could wish.
Today, many other obstacles to an Asimovian cosmos suggest themselves: the dustiness of the central galactic areas, the likelihood of perturbation of planetary orbits in so crowded a region (almost guaranteed to abort the formation of an earth-like planet), and above all the greedy black holes at galactic centers.
All told, it is highly improbable life would flourish in the busy centers of galaxies.
Since carbon is the sole element suitable to base life on (silicon, the only other candidate, doesn’t inspire much enthusiasm), we can safely say higher life forms will probably need an environment hospitable to carbon-based life—in other words, an earth-like planet.
A few years ago, for a school project (which, unfortunately I have misplaced), I made some conservative calculations of the chance of there being another earth-like planet in our galaxy. I began by eliminating from consideration all stars in multiple star systems (or in densely populated regions which would likely disrupt the stable planetary orbit needed for the survival of higher forms of life). This left me with less than half the starting population of stars, since binaries and other multiples make up the majority of stars we see. I then applied other factors.
At that time, about 100 extra-solar planets had been discovered. Because of eccentric orbits, star types, and masses, not one could conceivably support life as we know it. I took this to be characteristic of the galaxy as a whole, and estimated conservatively that perhaps one star in 50 might have a rocky planet with the carbon and trace elements necessary for life. We have now found almost 350 extra-solar planets and still not found a truly earth-like one.
This still left a huge pool of stars which could conceivably possess earth-like planets. But when I began to demand other essentials of life—water, for instance—the number dwindled. In the end, I decided I’d be surprised if there were another planet like good ol’ earth in our galaxy. The DVD Privileged Planet takes just a few necessities of life and leaves us looking at odds of one in 100 trillion. Since there are under 250 billion stars in our galaxy, those odds are pretty steep. They are also too conservative. Hugh Ross of Reasons to Believe has assembled a list of over one hundred essentials for higher life, which, if factored out, would make the chances of another earth-like planet infinitismal. The earth is such a special place that its development by a superior power seems almost proven.
So while the Foundation Trilogy makes a great yarn, one which I will almost certainly re-read yet again, Sci-Fi writers today need to readjust their premisses.
