Biosignatures are chemical or physical processes that indicate the presence of living organisms in a particular region. Astrobiology searches for life outside Earth and has gained attention since the Viking missions to Mars. The presence of liquid water is essential for life, and subsurface oceans have been discovered on moons of Jupiter and Saturn. Red dwarf stars are the most likely to possess habitable planets, and biosignature compounds include methane, nitrous oxide, chloromethane, and sulfur-based compounds. The broadening of biosignature theories suggests life may exist on planets previously thought to be inhospitable.
A biosignature is a chemical or physical process that can be detected from a distance and indicates the presence of living organisms in a particular region. The concept is often used in the field of astrobiology, which is a branch of biology that searches for life outside Earth’s terrestrial, aerial, and marine environments. The search for a biomarker to indicate the past or present existence of life on the planet Mars has gained increasing attention in astrobiology since the US Viking I and II missions were sent there to search for life between the mid-1970s and the early 1980s, and probes to other regions of the Solar System continued the search. The field has begun to expand since 2011, however, due to the fact that dozens of exoplanets have been discovered outside Earth’s solar system. A small minority of these planets are speculated to be Earth-like in size and structure, and may have an astrochemical biosignature indicating an ability to support life.
Understanding of the conditions necessary for planetary habitability by at least primitive life forms such as bacteria evolved in the 20th and 21st centuries. That’s because science has discovered the biosignature of organisms on Earth in regions like deep underwater volcanic vents that were previously thought to be completely inhospitable to all life forms. The resistance of such organisms to living in conditions absent of light and oxygen, and under extreme levels of temperature and pressure, suggests that the biosignature for life on other worlds may be broader than previously assumed.
The presence of liquid water is still considered essential for the existence of any form of life beyond the borders of the Earth. While liquid water was once thought to be rare in the Solar System existing only on Earth itself, this view has changed in the 21st century. Both Europa and Callisto, moons of the planet Jupiter, may possess subsurface liquid water oceans, and Enceladus, which is a moon of Saturn, is now known to have water-based volcanoes that can also support basic living organisms . The US Phoenix Mars Lander also found evidence of water-based ice in a region far from the polar ice caps on Mars in 2008, which could indicate a biosignature for bacterial activity that once existed or still barely exists under the surface of the red planet.
Detecting a biomarker for distant worlds is more challenging for current science as of 2011, as finding the worlds themselves is a challenge. The focus of research could begin by narrowing the range of star systems to those of red dwarfs. These are both the most common types of stars, making up about 75% of all stars in the Milky Way galaxy, and the most likely type to possess planetary systems that may be habitable due to their age and main-sequence presence. galaxy stars.
M-class dwarf stars are on average significantly smaller and cooler than Earth’s sun, so the planets that orbit them would need thick atmospheres to capture more light from their parent suns than Earth does. The probability suggests that, if life exists outside Earth, it would be more likely to be found on planets around red dwarfs than elsewhere. Classes of stars such as F, G and K, which are hotter and more luminous than the Sun, are also relatively rare compared to red dwarfs, so research is focusing on examining M-class stellar regions for planets with activity of biosignature.
Some gases singly or together would be a clear biosignature for the presence of potential life forms. These gases would also be longer-lived in the atmospheres of planets orbiting red dwarfs and easier to detect than planets orbiting hotter stars. These biosignature compounds include methane – CH4, nitrous oxide – N2O, chloromethane – CH3Cl, and ozone in the form of O2 or O3.
The detection of organisms on Earth living in sulfur environments near volcanic vents has also suggested that life can thrive on anoxic planets that are low in oxygen or completely devoid of oxygen. Organic sulfur compounds would therefore also be a strong indicator of life if detected in extraterrestrial atmospheres, including methanethiol – CH3SH and carbon disulfide – CS2. The presence of sulfur-based compounds would reflect biosignature theories about early life on Earth that existed before oxygen was widespread, and was a dominant life condition on Earth for at least 1,500,000,000 years.
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