Depending on which source of information we quote, the number of exoplanets—planets orbiting stars other than our sun—is experiencing an exponential population explosion. The longer we wait, the more exoplanets are discovered. Their number has roughly doubled every 27 months from the discovery of the first exoplanets in the 1990s. The population explosion is a function of the enhanced information sensing capabilities of our equipment. As time passes, we see farther; we see more clearly. Best of all, information concerning conditions on these exoplanets is revealed.
We have advanced from the days of early telescopes which could only detect and magnify images of visible light. The Spitzer Space Telescope, launched in 2003, works by observing certain wavelengths of infrared radiation, thereby making optically dark objects visible. All bodies in our universe emit infrared radiation at all times. Visible light is a minuscule portion of the electromagnetic spectrum. We observe wondrous images of our environment in visible light, but there is far more information available to scientists studying our universe by observing other wavelengths. There are many wavelengths longer and shorter than visible light. However, the human eye cannot see them.
In February exciting news hit the press. Around a fairly close ultra-cool star a mere 39 light years distant, scientists discovered seven generally earth-sized planets rapidly orbiting very close to their parent star named TRAPPIST-1. This star is less than one tenth the size of our sun and less than one quarter as warm. The Spitzer Space Telescope produced its images from infrared wavelengths emanating from the TRAPPIST-1 star and planetary system.
The most exciting element of this news focused on the planets’ existence in a possible “habitable zone.” The seven planets orbit quickly in a matter of days at a close distance from their cool parent star. They all revolve at less than the distance Earth’s planet Mercury orbits our Sun. Therefore, if some of the planets contain water, it is likely the water is liquid because of the not too hot, not too cold temperature on their surfaces. Scientists believe liquid water is necessary for any planet to sustain life.
We recall the excitement generated when the existence of first exoplanet was affirmed in 1992. Many students in my classroom had imagined that life, perhaps similar to Earth life, almost certainly existed somewhere else in our universe. The students of 25 years ago would be even more excited to know that some of the 3537 exoplanets in the immediate neighborhood of our huge Milky Way Galaxy in the past quarter century may have potential for intelligent life. This gripping notion seems more probable considering that many more billions of stars in our home Milky Way Galaxy certainly harbor planets. The possibility of other sites for intelligent life in our universe seems even more likely given our knowledge that over 100 billion galaxies exist in our vast universe!
Passion for the notion that many other sites of intelligent life exist on orbiting planets has been dampened, at least in our cosmic neighborhood. The stunning uniqueness of Earth life becomes increasingly obvious as we grasp the improbability that hundreds of just right physical planetary conditions must be present to support our vast array of life. Upwards of nine million species of complexly functioning organisms are embedded on this special planet. Eliminating even one required physical planetary condition precludes the possibility of human life, not to mention the life of nine million other species.
Whenever a discovery such as the science fiction-like TRAPPIST-1 discovery is made, scientists and laypeople alike rush to speculate on the possibility of extraterrestrial life. When my students inquired about my belief or disbelief in life anywhere else in the universe, I responded with an answer such as: “Not one intelligently produced signal has ever been received from outer space. If there are billions of instances of intelligent civilizations in our universe, at least one of them may have acquired the knowledge to communicate via radio or light signals if they were curious about the existence of other intelligent beings. But we have heard nothing at all.” For the past 150 years since the discovery of the electromagnetic spectrum and the invention of radio, Earth’s scientists have released billions of electromagnetic signals into space. Some signals have already reached the 3537 exoplanets discovered so far.
In February Seth Shostak, senior astronomer for the SETI institute noted “…The SETI Institute used its Allen Telescope Array (in 2016) to observe the environs of TRAPPIST-1, scanning through 10 billion radio channels in search of signals. No transmissions were detected although new observations are in the offing…” SETI stands for the Search for Extraterrestrial Intelligence. Nevertheless on February 22, 2017, Shostak wrote that the TRAPPIST-1 “…discovery has underlined the growing conviction that the universe is replete with real estate on which biology could both arise and flourish.” Read more about SETI and the search for extraterrestrial intelligence here:
We contrast Shostak’s unbridled optimism with our personal view. There are abundant reasons for dismissing the likelihood that any other planetary site in our universe could harbor life, even if it were blessed, for example, with the presence of liquid water and a reasonably friendly temperature. As we discover more and more stunning requirements for life possessed by Earth together with the absence of that array of requirements on even the most promising planetary systems, we realize anew the truth of Psalm 104:24 (The Message Translation): “What a wildly wonderful world, God! You made it all, with Wisdom at your side, made earth overflow with your wonderful creations.”