"Exploring the Possibility of Extraterrestrial Life in Our Vast Universe: Searching for Signs of Life in the Solar System and Beyond"

2023-04-19 07:17:28

Are we the only ones in the vast universe?

When you look up at the night sky in a quiet rural village or a place free of light pollution, you feel as if the stars are about to pour down. It is known that there are more than 600 stars in our observable universe, at least several times more than the number of grains of sand on every beach and desert in the world. The universe is arguably so large that it cannot be compared to the size we imagine. Indeed, do life exist only on Earth in this vast and vast universe? Carl E. Sagan, the author of ‘Cosmos’, also once said that if life exists only on Earth in this wide universe, it would be a huge waste of space.

It is known that there are at least several hundred billion planets in our galaxy. Of course, the actual number of planets could be much higher, given that the above numbers may be set by telescopes and current technology. Humanity has already found countless Earth-like planets among them, but it is currently impossible to approach the alien solar system with human technology. Therefore, astronomers are struggling to find more scientific and convincing evidence of extraterrestrial life through high-performance telescopes.

What about our solar system? Even the solar system is an object too large for the size of the Earth, but unlike the inaccessible outer solar system. This is because almost all objects in the solar system are accessible within a relatively few decades. Then, the remaining question will be which variables are the most important and what to observe from which celestial body in order to find another life in the solar system.

Is the birth of life easy?

The birth of intelligent life like humans is not an easy task not only in our solar system but also in other solar systems. First, if you look at the elements that make up humans, you can see that a supernova explosion has occurred nearby and a number of different elements must be supplied. For reference, this shows that we are descended from the stars. This is not a poetic or romantic expression. It’s just a scientific fact.

Even a nearby supernova explosion isn’t easy, but it’s just the beginning. Among the many planets that make up the (extraterrestrial) solar system, the planets must orbit at an appropriate distance from the sun to maintain a temperature friendly to life. In addition, there must be a process in which water and organic elements, which can be said to be the source of life, are transmitted through small bodies (comets, asteroids), etc. There must be a nearby planet to block it from approaching. This is because changing the orbits of small bodies in the solar system is so common that there is always a risk.

Of course, there must be a magnetic field on the above planet that can trap a lot of atmosphere on the planet to allow life to breathe. Like this, it is the birth of an intelligent life that is only possible when miracles are piled up on miracles. In the case of dinosaurs, they dominated the earth before humans, but as they are considered extinct due to the impact of an asteroid on the earth, continuous miracles are necessary for the stable evolution of life.

Earth is a friendly environment for life because it has a magnetic field. © NASA/Goddard/Conceptual Image Lab

On the other hand, the birth and evolution of microorganisms or primitive bacteria that are not normal life forms may be relatively easy. In particular, there may not even be a need for a lot of atmosphere if breathing with oxygen is not necessary, as is the case with many animals, including humans, currently living on Earth. Thus, some of the many miracles may not be necessary. For example, in the case of microorganisms, there are anaerobes that grow only in the absence of air. Anaerobic microorganisms that only need carbon dioxide to survive on Earth have already been discovered.

In conclusion, the extraterrestrial life we can find (or at least find easily), or other life in the solar system, will not be in the form of ETs or big-eyed green creatures as we would expect, but in the form of tiny microbes.

Searching for signs of life in the solar system

Humanity started looking for traces of various life forms in various celestial bodies in the solar system. Astronomers and biologists claim that as long as life exists in the volcanoes of the earth, life can live even in various adverse conditions if the right conditions are given. For example, in the case of Venus, where scientific evidence of active volcanic activity has been revealed, the surface temperature and atmospheric pressure are very high, which is very unfavorable for the evolution of life. However, studies have shown that life is likely to exist in Venus’ acidic clouds or in the sulfur dioxide-rich upper atmospheric layer of Venus that can absorb ultraviolet light. (Go to related article – “Active Volcanoes on Venus, Earth’s ‘Devil’s Twin’”)

The Mars rover Perseverance, which has been active on Mars since 2021, has collected two rock samples containing organic molecules that may be traces of ancient microbes from an ancient delta region on Mars’ northwestern edge. The research team confirmed that the above rocks contained sulfate minerals and organic molecular layers together, and said that the above sulfate minerals appeared to have been deposited together as the lake evaporated. As sulfate deposits on Earth are often known to harbor traces of life, the possibility of life on Mars increases as a result.

Organic matter centered on carbon can be created regardless of life, but it is often regarded as a trace of life because it often exists together with oxygen, nitrogen, and phosphorus. If more complex organic molecules, such as proteins or amino acids, are found in the stomach, the evidence for (past) life is stronger.

The Mars rover Perseverance collected organic molecules. © Perseverance/JPL/NASA

water is the most important substance

However, the most important substance in finding traces of life is water, which is considered to be the source of life. Water is the most important substance among the substances that make up living things. Of course, it’s possible that there could be life that doesn’t need water, or that doesn’t involve water at all, but we don’t know of such life forms yet. Therefore, in order to find life forms other than humans on celestial bodies other than Earth, it is necessary to find an environment with water first. In particular, water must be able to exist on the surface of a planet or celestial body.

Water has several special properties because of hydrogen bonding. For example, water, which has a very large heat capacity (the heat required to raise the temperature of a substance by 1 degree), has a relatively small temperature change. This allows life to maintain a fairly stable internal temperature. Also, water has a significantly higher boiling point than other liquids of the same molecular weight. Because of this, it is possible to exist in a liquid state over a fairly wide range of temperatures. Hydrogen bonds in water can dissolve many substances due to their electrical properties.

Model of hydrogen bonding between water molecules (1) Schematic diagram © Qwerter

Therefore, the probability that life can exist is very high in places where traces of water have been found among celestial bodies in the solar system or where water has been found. Specifically, water exists in the form of ice because the temperature decreases as it moves away from the sun. In addition, places where comets are born, such as the Kuiper belt or the Oort cloud, the second dusty disk of the solar system, deliver various materials in the form of ice to various planets or moons.