The search for extraterrestrial life
3 April 2023
We have allowed our thoughts to wander to thoughts of faraway worlds populated by beings who are not like us for as long as humans have looked to the night sky for divine meaning and a place in the universe. The first Western thinkers to seriously consider the possibility of an infinite universe with an infinite number of civilizations were the ancient Greeks. The Copernican model of a heliocentric solar system, developed in the 16th century, opened the door to a wide range of extraterrestrial speculations (who was to say that God hadn’t set other life-sustaining worlds in motion when the Earth was no longer at the center of creation? That way of thinking never went over well with the church. However, during the Enlightenment and into the twentieth century, speculation about alien life kept up with scientific research.
However, it wasn’t until the end of the 1950s that anyone came up with a plausible strategy for looking for these fictitious neighbors who were far away. Science was eager to learn what lay beyond the confines of our thin, insulating atmosphere as the space age began. The initial three Sputnik satellites had been launched into Earth orbit by the Russians in 1957 and 1958; In 1960, the successful Pioneer 5 interplanetary probe was scheduled to launch toward Venus. We were preparing machines to travel farther than the majority of us could imagine, but given the vastness of space, we would not be any closer to unknown planetary systems than if we had never left Earth.
Our only option was to hope that intelligent life had established itself somewhere else and progressed far beyond our technological capabilities to the point where they could communicate with us via the empty space plains. The problem we had was figuring out which phone might be ringing and exactly how to answer it. Thus, in the middle of September 1959, two young Cornell University physicists published a two-page Nature magazine article titled “Searching for Interstellar Communications.” That was the beginning of the modern search for extraterrestrial life, and life on Earth would never be the same again.
Two Cornell physicists, Giuseppe Cocconi and Philip Morrison, began their 1959 article in Nature magazine with frankness: Although we cannot rule out the possibility of intelligent life elsewhere in the universe, we are unable to accurately estimate its likelihood. Since we have evolved and are intelligent, it stands to reason that other civilizations could develop on planets in the vicinity of other sun-like stars. Some of those civilizations would most likely be older and more advanced than ours, and they would recognize our Sun as a star that might be home to life and want to get in touch with us. The main question of the paper was as follows: What means would they use to convey their message? The choice of electromagnetic waves was the most logical. They would not disperse over the vast distances between stars because they travel at the speed of light. But how frequently? Since it would be impossible to scan the entire electromagnetic spectrum, they made an assumption that has remained central to SETI research ever since. At 1420 MHz, which is the emission frequency of hydrogen, the most abundant element in the universe, they would listen in. They reasoned that it was the only obvious astronomical trait that we and an unknown civilization would share, and that they would also recognize it.
Cocconi and Morrison’s hazy assumptions were transformed into a genuine mathematical equation just a few years later, in 1961. Frank Drake, shown here with the equation, and a few other astronomers and scientists, including Carl Sagan, gathered in Green Bank, West Virginia, to work out the formula and variables needed to estimate the number of intelligent civilizations in our galaxy. It turns out that when you assign numbers to hazy assumptions, you get an answer with enough variance to make you wonder if you were really trying to clarify those assumptions in the first place. From fewer than a thousand to nearly a billion, the group proposed a range. You might think that the formula would have changed over time, but it hasn’t. Even though “held up” is a relative term for such a hazy equation, it has held up surprisingly well. Since the 1960s, data that can be used to support the initial estimates of measurable quantities like the frequency with which sun-like stars form and the number of those stars with planets has demonstrated that those estimates were fairly accurate. The remaining variables, such as the proportion of life that eventually develops intelligence and the average lifespan of an intelligent civilization, will never be quantified. However, despite being contentious, the equation has been the focus of SETI investigations for a long time and continues to be a useful framework.
It is safe to assume that we will not encounter any tiny green men on Mars. A grey humanoid with almond-shaped black onyx eyes and elongated skulls is also unlikely to be encountered. However, there is a good chance that we will discover alien life in the form of extremophiles or bacteria, which are bacteria-like organisms that are able to live in environments that appear to be hostile. From Mariner 4 in 1965 to the Phoenix mission, which landed in the polar region of Mars in May and continues to send back a tremendous amount of data, we have sent a variety of landers, orbiters, and probes there. One of the three keys to extraterrestrial life, water—whether ice or liquid—is the first thing we’re looking for. Senior Astronomer at the SETI Institute, Dr. Seth Shostak, states, “I think it’s probably the best bet for life nearby.” You could make the case that some of Jupiter’s moons, such as Europa, Ganymede, and Callisto, or Saturn’s moons Titan and Enceladus, may have life.