In this blog post, we will look at the possibility of extraterrestrial life and the scientific approach to space exploration, focusing on Drake’s equation.
One of the most important initial conditions in the search for extraterrestrial life is to confirm the presence of carbon and liquid water on the target planet or moon. This is because these are the basic criteria for determining whether the elements necessary for life exist.
First, carbon has the property of easily combining with various elements to form organic compounds. These organic compounds are the basic substances that make up the structure of living organisms and play an important role in synthesizing various substances essential for life. For example, most molecules necessary for life, such as DNA, proteins, and fats, are composed mainly of carbon. Therefore, the presence of carbon is an important clue suggesting the possibility of life in that environment.
Water is also a key factor in determining the possibility of life. Water is one of the rare substances that can exist in a liquid state over a wide range of temperatures, and it acts as a medium that mediates or promotes various chemical reactions that occur within living organisms. Living organisms constantly undergo physical and chemical reactions within themselves to generate energy and circulate substances, and liquid water is essential for this process. Since life cannot be sustained or evolve in an environment without water, the presence of water is a decisive factor in the search for extraterrestrial life.
In addition, in order to confirm the existence of life, it is necessary to analyze whether specific chemicals are being consumed in the environment. This is a method of confirming signs of metabolism, which is one of the key characteristics of life. Living organisms constantly take in energy and substances from the outside and convert them internally to sustain their life activities. This metabolic process causes chemical changes in the surrounding environment, which can be detected as changes in the concentration of certain substances. Therefore, if certain chemicals are missing or present in abnormal proportions in an extraterrestrial environment, this could be a strong clue to the existence of life.
There are several celestial bodies within the solar system that are considered to have a relatively high probability of harboring life. A prime example is Mars. Mars has geological evidence that suggests it may have once had water, and there is speculation that water may still exist in the polar regions or underground. In addition, Jupiter’s moon Europa and Saturn’s moon Titan are also considered prime targets for the search for extraterrestrial life. These moons may have liquid oceans beneath their surfaces, and Titan has a unique environment with methane lakes and rivers on its surface. For these reasons, many probes have already been sent to these celestial bodies, and various international exploration projects are planned for the future, so the search for clues to extraterrestrial life will continue. If life is confirmed on even one of these worlds, it will be a turning point for human civilization. This is because it would extend the conventional wisdom that life can only arise in the unique environment of Earth to a generalized theory that life can arise anywhere in the universe if the right conditions are met.
For extraterrestrial life to exist outside the solar system, i.e., in an exoplanetary system, several essential conditions must be met. The most basic premise is that planets capable of supporting life like Earth must orbit a star similar to the Sun. This is because stars provide adequate light and heat to form a “habitable zone” where liquid water can exist on the surface of a planet.
Through astronomical research and technological advances in recent decades, it is becoming increasingly clear that exoplanetary systems similar to our solar system exist. However, exoplanets are very difficult to observe directly because they do not emit light themselves. Instead, indirect methods are used, such as analyzing changes in the position or brightness of a star caused by minute gravitational changes that occur when these planets revolve around it, or observing the phenomenon of “transit” that occurs when a planet blocks the star.
Since the discovery of the first exoplanet in 1994, hundreds of exoplanets have been discovered, and the number continues to grow. Many of these are large, heavy gas planets like Jupiter, and relatively few rocky planets similar to Earth have been found. However, as observation technology becomes more precise, the possibility of discovering Earth-like planets is steadily increasing.
Currently, various projects are actively underway to find exoplanets using large telescopes on Earth. In particular, ground-based telescopes are limited by atmospheric effects, so space telescopes are being developed to overcome this limitation, and several telescopes have already been launched or are scheduled for launch. Among them, a notable project is the Terrestrial Planet Finder developed by the National Aeronautics and Space Administration (NASA). This searcher was developed with a target launch date of 2014 and will operate five large telescopes with a diameter of 3.5 meters in formation in space to perform the mission of precisely searching around exoplanets. The ultimate goal of this searcher is to directly observe exoplanets with conditions similar to Earth and detect substances in their atmospheres that could be signs of life, such as oxygen, ozone, and methane.
Furthermore, assuming that extraterrestrial life exists, if that life has long-range communication technology, another way to confirm its existence is through radio wave detection. If advanced civilizations use radio waves to communicate, the radio signals they send are likely to have certain patterns or repetitions that differ from naturally occurring random radio waves. In particular, since they would use powerful radio waves to maximize communication efficiency, these signals can be relatively easily detected by detection equipment.
There are two ways to search for radio signals. One is to quickly scan the entire sky to survey a wide area, and the other is to search intensively in a narrow area around a specific star or stars. Both methods are strategies for detecting radio waves that could be sent by extraterrestrial intelligent life, and they are used in parallel depending on the purpose of the search and the technical conditions.
Generally, the composition and characteristics of celestial bodies and interstellar gas are revealed by analyzing the radio waves emitted from them. In particular, hydrogen atoms (H) and hydroxyl groups (OH) are widely distributed throughout our galaxy, and these two molecules are also the main components of water (H₂O). The radio waves emitted by hydrogen atoms have a frequency of approximately 1,420 MHz, while those emitted by hydroxyl groups have a frequency of approximately 1,721 MHz. The frequency band between these two frequencies is called the “water hole.” This frequency band has little radio wave interference and is considered to be very suitable for radio communication as it is the region where the main molecules in the galaxy exist. Therefore, experts believe that if extraterrestrial life exists, it is highly likely that they would use this frequency band to send signals.
Based on this assumption, in 1960, Frank Drake conducted Project Ozma, which used a 26-meter radio telescope at the National Radio Astronomy Observatory to search for extraterrestrial radio signals from approximately 500 stars near the sun. This is considered the beginning of the scientifically organized search for extraterrestrial intelligent life. Subsequently, in 1984, the SETI (Search for Extra-Terrestrial Intelligence) research institute was established to specialize in the search for extraterrestrial intelligent life. Precise exploration work is underway to select candidates for radio signals that may have been sent by extraterrestrial life forms by analyzing repetitive radio signals, changes in intensity at specific frequencies, and the direction and distribution of signals.
So, how many advanced extraterrestrial civilizations capable of communicating with us exist in our galaxy? To provide a scientific estimate, Frank Drake devised a formula known as the Drake Equation. This equation is composed of the following factors:
The rate of star formation suitable for life within our galaxy
The probability of a star having planets
The number of planets with conditions suitable for life
The probability of life actually occurring on those planets
The probability of life evolving into intelligent life
The probability of intelligent life developing communication technology
And how long such a civilization can survive, or its “lifespan.”
The Drake equation is not so much a mathematical model as a scientific framework for predicting the number of extraterrestrial civilizations. Drake himself acknowledged that most of the variables in this equation are still uncertain and that it is impossible to substitute exact figures. Nevertheless, as humanity’s knowledge of space science gradually accumulates, it is hoped that this equation will provide clues to the number of extraterrestrial civilizations within our galaxy that are capable of communicating with us.
