Last week the Kepler Mission blasted off into space—or as NASA nicely put it, “vaulted into the heavens on a column of thunder”—and within a few days passed the orbit of the moon. On March 12 its photometer was powered on, and as soon as it can be calibrated it will begin fulfilling the mission’s purpose: the search for other worlds.
This is not a no-brainer. It was only in 1995 that the first “extrasolar” planet was proven; now we know of over three hundred of them, but there should be a great many more.
How many? There are roughly a hundred billion stars in our Milky Way galaxy, and about one percent of them should have earth-like planets—that is, planets in the earth’s size range and in the “habitable zone” of their respective stars. That means a hundred million planets where life could have evolved inside the Milky Way.
Oh, did I mention that there are hundreds of billions of galaxies in the universe?
These sorts of numbers were first brought to public attention by Carl Sagan, who collaborated with the Russian astronomer I.S. Shklovskii in the 1960s on a path-breaking book called Intelligent Life in the Universe. Using conservative assumptions about the numbers mentioned above, and reasonable assumptions about the origins of life and the process of evolution, they concluded that there is little chance that we are alone.
Kepler—named for the great astronomer whose elegant equations precisely described the motion of the planets in our solar system—will greatly improve on the methods used to discover new planets from the ground. In the three and a half years of the mission, exploring only a small part of our galaxy, it is expected to turn up fifty earth-like planets.
Will there be life on any of those? I would be surprised if there weren’t. There will not be creatures exactly like those on earth, at least not above the level of viruses. But there should be something resembling bacteria, plants, and animals, if not on one of those fifty planets then on one of the hundreds more that will be found in coming decades.
Evolution is not deterministic, but it is what might be called probabilistically deterministic. In this Darwin anniversary year, we should recognize that if there is enough time—and there is enough time—life will originate by the same processes that brought it about here.
Under conditions that will prove to be common, organic molecules inevitably form from carbon, hydrogen, oxygen, nitrogen, phosphorus, and other elements that will be available on these planets. Nitrogen-containing aromatic hydrocarbons will eventually be among them, and from some of these (the purines and pyrimidines) there eventually will emerge self-replicating, information-containing strings.
According to the Second Law of Thermodynamics, these orderly molecules should be torn down and returned to disorder through ever-increasing entropy, but some of them—the ones containing the best information about how to resist the forces of disorder—survive and reproduce. The rest is evolutionary history.
Life may be much closer than even the nearest star. In January another group of NASA scientists held a press conference to announce their discovery of large amounts of methane on Mars. Methane is the simplest organic compound, consisting of a carbon atom with four hydrogen atoms attached. It need not be a sign of life, since under certain conditions it will form spontaneously from carbon dioxide and hydrogen.
But on earth at least, the vast majority of methane is produced by living things, including bacteria. And the amount of methane recently found on Mars may mean that bacteria now live below the surface of that planet. Other places in the solar system, especially Europa, a moon of Jupiter, and Titan, a moon of Saturn, are possible settings for simple life.
But if not here in our solar system, certainly (we use the word for a lot less certain things) elsewhere in the universe, and almost certainly in our galaxy. As for intelligent life, I am confident it is there.
Or was. Because as Shklovskii and Sagan recognized, intelligent beings within a few hundred thousand years will gain the means to destroy life, or at least intelligent life, on whatever planet they find themselves. This is the most imponderable term in the equation: what percentage of civilizations can develop protection from their most dangerous enemy, themselves?
It’s a question we must soon answer here.