This article was originally published in conversation. The publication contributed this article to Space.com Expert Voices: Columns and Insights.
There is only one example of biological formation in the universe—life on Earth. But what if life could have formed in other ways? How do you search for alien life when you don’t know what it looks like?
These questions have attracted the attention of astrobiologists, scientists who search for extraterrestrial life Earth. Astrobiologists attempt to propose universal rules to govern the emergence of complex physical and biological systems on and off Earth.
I’m an astronomer and have written extensively about astrobiology. Through my research, I learned that the most abundant alien life forms may be microorganisms, since single cells are easier to form than larger organisms. But just in case there is advanced alien life out there, I’m on an international advisory committee that designs the messages to be sent to these civilizations.
Detecting life beyond Earth
Since the first discovery exoplanet In 1995, more than 5,000 exoplanets, or planets orbiting other planets Starhas been discovered.
Many exoplanets are small and rocky like Earth and lie within the habitable zone of their stars. this habitable zone It is the range of distances between a planet’s surface and its orbiting star that allows a planet to host liquid water, thereby supporting life on Earth.
The exoplanet samples detected so far suggest that there are 300 million potential biological experiments in our galaxy, or 300 million places, including exoplanets and other celestial bodies such as moons, with conditions suitable for the emergence of life.
Researchers’ uncertainty begins with the definition of life. It feels like defining life should be easy because we know life when we see it, whether it’s a bird flying or a microbe moving in a drop of water. But scientists don’t agree on a definition, and some say a comprehensive definition may not be possible.
NASA Define life as “self-sustaining chemical reactions capable of realizing Darwinian evolution.” This means that living organisms have complex chemical systems that evolve by adapting to their environment. Darwin’s theory of evolution believes that the survival of organisms depends on their adaptability to the environment.
Life on Earth has evolved over billions of years, from single-cell organisms to large animals and other species, including humans.
Exoplanets are distant and hundreds of millions of times dimmer than their parent stars, making them challenging to study. Astronomers can use spectroscopic methods to examine the atmospheres and surfaces of Earth-like exoplanets to look for chemical signatures of life.
Spectroscopy can detect signatures of oxygen (the microorganisms known as blue-green algae were produced by photosynthesis on Earth billions of years ago) or chlorophyll signatures (indicative of plant life) in a planet’s atmosphere.
NASA’s definition of life raises some important but unanswered questions. Is Darwin’s theory of evolution universal? What chemical reactions could lead to the creation of life beyond Earth?
evolution and complexity
All life on Earth, from fungal spores to blue whales, evolved from the last common ancestor of microorganisms some 4 billion years ago.
The same chemical processes occur in all organisms on Earth, and these processes may be universal. They may be completely different elsewhere as well.
In October 2024, a diverse group of scientists came together to think outside the box about evolution. They want to step back and explore what processes create order universe Whether it’s biological or not, find out how to study the emergence of life completely different from life on Earth.
The two researchers propose that complex chemical or mineral systems evolve to store more information when placed in an environment that allows some configurations to persist better than others. as time Over time, systems will become more diverse and complex, acquiring the functions necessary for survival through a kind of natural selection.
They speculated that there might be a law describing the evolution of various physical systems. Biological evolution through natural selection is just one example of this broader law.
In biology, messages are the instructions stored in the sequence of nucleotides on the DNA molecule, which together make up the genome of an organism and determine its appearance and function.
If you define complexity using information theory, natural selection will cause the genome to become more complex because it stores more information about its environment.
Complexity may help measure the line between life and nonlife.
However, it would be wrong to conclude that animals are more complex than microorganisms. Biological information increases with genome size, but evolutionary information density decreases. Evolutionary information density is the fraction of functional genes within a genome, or the fraction of total genetic material that expresses adaptation to the environment.
The genomes of organisms thought to be primitive, such as bacteria, have high information density and therefore appear to be better designed than those of plants or animals.
A universal theory of life remains elusive. Such a theory would include concepts of complexity and information storage, but it would not be tied to DNA or the specific types of cells we find in terrestrial biology.
Researchers have explored alternatives to terrestrial biochemistry. All known organisms, from bacteria to humans, contain water, which is an essential solvent for life on Earth. A solvent is a liquid medium that facilitates chemical reactions that create life. But it’s also possible that life could have emerged from other solvents.
Astrobiologists William Baines and Sarah Seager explore thousands of molecules that may be related to life. Possible solvents include sulfuric acid, ammonia, liquid carbon dioxide, and even liquid sulfur.
Alien life may not be based on carbon, which forms the backbone of all life’s basic molecules—at least on Earth. It might not even need a planet to survive.
Advanced life forms on alien planets may be so strange that they are impossible to identify. When astrobiologists try to detect life beyond Earth, they need to get creative.
One strategy is to measure the mineral signatures of exoplanet rocky surfaces, because mineral diversity tracks the evolution of terrestrial life. As life evolved on Earth, it used and created minerals for exoskeletons and habitats. The 100 minerals present when life first formed have grown to approximately 5,000 today.
Zircon, for example, is a simple silicate crystal that dates back to before the beginning of life. Zircons found in Australia are the oldest known fragments of Earth’s crust. But other minerals, such as apatite, a complex calcium phosphate mineral, are produced biologically. Apatite is a major component of bones, teeth and fish scales.
Another strategy for searching for life different from Earth’s is to detect evidence of civilization, such as artificial light or the industrial pollutant nitrogen dioxide in the atmosphere. These are examples of tracers of intelligent life known as technological signatures.
It’s unclear how and when the first discovery of life beyond Earth will occur. it may be in solar systemeither by sniffing the atmospheres of exoplanets or by detecting man-made radio signals from distant civilizations.
Searching is a winding road, not a smooth road. This is true for life as we know it – and for life as we don’t know, all bets are off.
This article was originally published in dialogue. read Original article. Follow all Expert Voices issues and debates – and be part of the discussion – Facebook, twitter and Google+. The views expressed are those of the author and do not necessarily reflect those of the publisher. This version of the article was originally published on Space Network.