Is There Anyone Else in the Universe?
“Is there life in space?” The question has been one of humanity’s favourites, with an increasing interest for centuries. When we look at the stars in the sky, the magical mystery of an endless universe comes alive in our minds. In the last century, humanity has taken great steps in finding answers to this question, with the help of advances in space exploration.
Mankind’s interest in searching for extra-terrestrial life goes back at least as far as known history. While ancient civilizations associated the bright dots in the sky with the gods, modern scientists use more technologically advanced tools to explore space and understand the depths of the universe. Space observations gained an entirely new dimension with the invention of telescopes, helping us learn more about planets, stars and galaxies.
First, let’s take a look at some of the methods scientists use to look for signs of life beyond the Earth…
Remote-sensing is a technique involving remote observation to detect signs of life in space. Telescopes and other observing instruments collect radiation from different parts of the electromagnetic spectrum. Scientists analyse this radiation to look for traces of molecules known as biomarkers in the atmospheres of planets. The presence of certain gases like oxygen, methane and ozone may indicate the possible presence of life on a planet.
Spectroscopy is a technique that involves analysing wavelengths of electromagnetic radiation. Data obtained from the atmospheres of planets or the light spectra of stars are used for determining the presence of certain types of molecules. Scientists try to detect the presence of compounds associated with life, including water vapour, carbon dioxide, ammonia, and methane in particular.
Transit Photometry aims to detect the presence of planets by measuring drops of starlight caused by a planet while it passes between its star and the observation instrument. Decreases in a star’s brightness indicate that all or part of the planet is passing in front of it. Periodic repetition of these drops can reveal the existence and the size of a planet.
Radial Velocity is a method that aims to detect velocity changes in the motion of a star due to the influence of planets orbiting it. A planet orbiting a star causes the star to wobble because of its gravitational pull. The wobbling results in minor shifts in the amount of observed starlight, which may provide information about the planet’s mass and orbit.
Biomarkers are signs that may indicate the existence of life. Scientists look for biomarkers in the atmospheres of distant planets, or in data from other celestial bodies. Common biomarkers include oxygen, methane, or other gases that living organisms can produce. Advanced telescopes such as the James Webb Space Telescope aim to detect the atmospheric composition of distant planets in greater detail.
Scientists use various strategies to identify habitable zones by examining the basic necessities of life. For a planet to be habitable, the existence of elements such as water, energy and chemical compounds is important. For example, researches on Mars indicate the presence of water in the past, and that the planet was potentially habitable. Likewise, the underwater oceans on Jupiter’s moon Europa offer a potentially habitable environment for microorganisms.
The most important condition for life to exist -as we know it- is the presence of surface water on a planet. One of the most important criteria for choosing a potentially habitable exoplanet to focus studies on is that the planet should be in the “habitable zone”. The habitable zone refers to the distance from a star at which water could exist in liquid form on orbiting planets’ surfaces –which is a decisive factor in the search for life. Scientists acknowledge that the existence of water is necessary for life. Water is an essential component and medium for biochemical reactions to take place, the nutrients to be transported, and the organisms to survive.
After an exoplanet is detected by transit photometry, and its orbit is confirmed to be in the habitable zone, its atmosphere is examined by spectroscopy.
Spectroscopy allows analysing the chemical compounds in the planet’s atmosphere and even the emission or absorption patterns of light to detect potential signs of life. The best, and perhaps the only way to gain insight on how life may have begun on other worlds is to understand how it originated in the place we know the best, on Earth.
For more in-depth information about how life began on Earth, you may read our previous article On the Origin of Life.
Extremophiles
Regarding the search for life in space, an important subject to consider is the extremophiles. These refer to microorganisms that are able to live in extreme conditions and thus may be found in environments dominated by high temperature, low temperature, high pressure, high salinity, and acidic or alkaline pH.
Extremophiles constitute significant models in the search for extra-terrestrial life due to the ability of these organisms to survive in very limited physical and chemical conditions. This could help us understand the potential life forms in space. Considering the possible extreme conditions on planets and moons in outer space, the adaptive abilities of extremophile organisms may increase the likelihood of life existing in these far-away worlds.
Additionally, extremophiles may contribute to the interplanetary panspermia theory. This theory suggests that life can be propagated through space from one location to another via events like an asteroid impact or a comet pass-by. Due to their ability to survive in space, extremophiles can ensure the preservation of microorganisms during such transports. Organic molecules found on the asteroid Ryugu, described in our article Stones from Space, support this idea.
Such extreme life forms show us that we may be able to find some traces of life in celestial bodies located outside habitable zones. Therefore, studying the surfaces and internal structures of planets is important in the search for life.
Mars is one of the focal points of research in our own Solar System. The majority of Mars, and research tools such as Curiosity and Perseverance, are used for studying the planet’s geology, atmosphere, and its past or present “potential” habitability. Finding traces of ancient microbial life on Mars is one of the key goals of NASA’s Mars Sample-Return mission.
Europa and Enceladus, the respective moons of Jupiter and Saturn, are thought to have oceans of liquid water under the icy crusts on their surface. These satellites are of great interest as they can host environments suitable for life. Future missions, such as NASA’s Europa Clipper and the currently proposed Enceladus Life Finder, aim to explore these moons and look for signs of life.
Until now, searching for carbon-based life forms has been a priority, as most of the known life forms on Earth rely on carbon. However, it is important to consider that carbon-based life is not the only option, and thus scientists use different approaches to search for non-carbon life. First, they assume that other elements, particularly nitrogen, phosphorus, sulphur and silicon could also be used as basic building blocks of life instead of carbon. These elements are known to have properties similar to those of carbon in their ability to provide chemical diversity and complexity.
In order to investigate unknown life forms, it is necessary to expand biosignatures. This can be done by investigating different gases, chemical imbalances, or other indications to detect traces of potential non-carbon life forms.
However, there is great uncertainty in the process of research and discovery, as we do not know exactly what non-carbon life looks like. Therefore, we need further research, more technological advancement, and observation strategies to search for these in space. Even though there is no definitive proof regarding the existence of non-carbon life, scientists keep an open mind to this possibility.
SETI
The main point of techniques and developments we have described so far was to find biological traces of extra-terrestrial life. SETI (Search for Extra-terrestrial Intelligence), one of the first important projects in this field, is research to detect traces of extra-terrestrial intelligence. The main goal of SETI is to actively work to detect artificial signals from other planets or stars and to demonstrate the presence of a potentially intelligent civilization with these signals.
This never-ending quest serves the purpose of understanding humanity’s place in the universe. Plus, the search for life in space supports technological progress and contributes to the development of new tools for space exploration and observation.
As a result, the search for life in outer space is a topic of great interest and excitement in popular science. Scientists search for potential traces of life through a variety of studies, including space telescopes, planetary characterization, and Solar System exploration missions. Although there is no definitive proof yet, the data obtained so far suggest that the probability of life in the universe is high. The search for extra-terrestrial life represents our place in the universe and our efforts to unravel the secrets of the universe.
REFERENCES
- 1. https://www.astronomy.com/science/how-well-find-life-in-the-universe/
- 2. https://www.esa.int/Science_Exploration/Space_Science/COROT/The_search_for_life
- 3. https://exoplanets.nasa.gov/search-for-life/can-we-find-life/#otp_how_will_we_find_life?
- 4. https://www.scientificamerican.com/article/the-search-for-extraterrestrial-life-as-we-dont-know-it/