NASA
Modern Thoughts About Intelligent Life in Our Solar System
In order for life to establish itself and thrive, three things are necessary: free liquid (water is best); organic compounds; and energy, to build organic compounds from present molecules. Water (or water vapor) is a vehicle. Key organic compounds, and those that define all life as we understand it, are carbon, oxygen, and hydrogen, with lesser but significant amounts of sulfur, phosphorous, and nitrogen, plus trace amounts of dozens more. And what of the energy needed for life? The famed 1952 Miller-Urey experiment (conducted by University of Chicago graduate chemistry student Stanley Miller under the supervision of Harold Urey) placed a carefully considered mixture of water vapor, hydrogen gas, methane, and ammonia into a beaker. In a simulation of lightning coursing through the atmosphere of a primordial Earth, Miller sent an electric charge through the mixture. Within days, the beaker produced visible amino acids, which are essential to the creation of proteins. According to the Miller theorem, life begins, and continues, as a chemical process. Further, because the process can be started by things as common as lightning or element- rich volcanic eruptions, the beginnings of life are probably not unique to Earth.
Although many—if not most—of the universe’s planets have not produced life, the probability of extraterrestrial life is nevertheless high.
Molecules here on Earth developed from a coordination of amino acids, fatty acids, and sugars, which created nucleic acids that directed proteins to manufacture self-replicating cells. Although we understand the roles of the basic building blocks, the way in which proteins “got the message” remains a mystery.
Further, human understanding of the specific types of early microorganisms is hazy at best. Still, we surmise that very simple forms of life, bacteria, evolved into other, more sophisticated forms. Assuming that bacteria developed and evolved on planets other than Earth, it is not unreasonable to suggest that sophisticated life forms exist (or have existed) elsewhere in the universe. Of course, a bacterium is a “sophisticated life form”; likewise an amoeba, a mold spore, and yeasts. There are no “simple life forms.” Even the humblest-seeming form of life is incredibly complex. And when we turn our attention to plant life, marine life, animal life, and to ourselves, we are in realms of almost unimaginable complexity.
Other planets of our solar system hold only modest promise of any life at all, and virtually none for intelligent life. Although the giant planets of the outer solar system—Jupiter, Saturn, Uranus, and Neptune—are enormous contrasted to Earth (even the smallest of the giants, Neptune, is nearly four times the size of our planet), the giants have far less overall density, and are less massive than their sizes suggest. Little on these planets is solid. Jupiter, for instance, is mainly a swirl of liquid hydrogen. Because that liquid also contains water, ammonia, and methane, primitive bacteriological life could exist there. For more advanced life to germinate and take hold, however, a planet needs oceans (where life develops) and dry land (where life migrates and evolves). Even when we stretch the limits of speculation, and known science, to consider intelligent life on Jupiter and the other giants, the planets’ lack of solid surfaces mandates the evolution of intelligent life quite different from ours—one, for instance, denied the capability to construct buildings or manufacture spaceships. Our solar system’s other planets (including the dwarf planet, Pluto) are too hot or too cold to encourage life as we understand it.
Europa, a moon of Jupiter, has an ice-covered ocean that may support microbial life. Titan, the largest moon of Saturn, is the only satellite in our solar system to have a significant atmosphere. Life may have secreted itself there.
Perhaps the most compelling argument against intelligent life in our solar system is that the distances between planets are not great. (The enormous distance separating Earth from “Planet Nine” is another matter, and will be discussed in this book’s afterword.) Communication from one party or another should already have been achieved. Instead, there is silence (other than random radio signals) from Earth’s sister planets, and no visual evidence of agriculture, terraforming, or other intelligence-based alterations to the planets’ surfaces or atmospheres. (Europa, its surface decorated with spidery red tracers, may be the exception.) The only possible sentient life is akin to the sort already discussed: a liquid, gaseous, or other form, lacking manufacturing capability. If such life exists in our solar system, evolution forces it to remain silent and unidentifiable, and almost certainly unaware that we are here.
