If aliens do exist, they would likely live on rocky planets similar to ours. However, new research suggests a new type of habitable planet that is very different from Earth.
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Earth is the only functional model that we have of a world habitable. Astrobiologists are therefore hopeful that they will find evidence of extraterrestrials living on exoplanets rocky Earth-like. Our planet's size, chemical composition, temperature and position in the solar system make it friendly for life.
New research in The Astrophysical Journal has suggested that a new class of planets, called Hycean worlds could also be habitable. Although this type of planet is not found in our solar system they are quite common in the galaxy. These planets are basically what you would expect from Earth and Neptune having a baby. They're large and warm and have an atmosphere filled with hydrogen. The oceans that cover them are huge.
New research suggests that Hycean planets could be habitable, and that oceans can support microbial life or other complex life. The researchers, led Nikku Madhusudhan, from Cambridges Institute of Astronomy proposed a set of biosignatures for astronomers to look out for when studying these planets. They also included a list of potential Hycean candidates near them (cosmologically speaking).
Madhusudhan invented the term Hycean. It is a portma-nteau of hydrogen and ocean. He explained it to me via email. While studying K2-18b, a potentially habitable mini Neptune, the astronomer came up this idea. Madhusudhan was intrigued by the exoplanet's conditions. He and his colleagues began a deeper investigation to determine if mini-Neptunes could be habitable.
Since the 1990s, thousands of exoplanets were discovered. The vast majority of them are low-mass planets that are between one and four times the Earth's size. The new study was focused on mini-Neptunes. These are smaller than Neptune, but approximately 1.6 times larger than Earth.
According to the study, these objects are smaller than ice-giants but too big to have rocky interiors such as super-Earths. Mini-Neptune interiors can be habitable if they are cooled with the right properties. This has been proven by past explorations.
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The proposed class of habitable exoplanets can grow to be 2.6 times larger than Earth and have temperatures of 392 Fahrenheit (200 Celsius). Madhusudhan answered the question, "The presence of liquid water as the surface of Hycean worlds would be covered by ocean", and said that the atmosphere is hydrogen-rich, which provides both protection from harmful radiation and the necessary surface conditions.
Madhusudhan stated that Hycean worlds can exist in the vicinity of a variety of star types. Madhusudhan believes that a Hycean exoplanet locked to tidal is likely to be habitable even though it never faces its host star. (The researchers call these exoplanets Dark Hycean planets, which sounds very sci-fi). Madhusudhan stated that these exoplanets must have the chemical properties necessary to support microbial life. However, it is not clear if the planets will be able to produce and sustain this kind of life.
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Although the surface conditions can affect the depth to which life may exist in Hycean oceans, researchers believe that life could be found deeper than the ocean floor. If this life does exist, it would be microbial in nature. Madhusudhan stated that it is open to question whether or not more complex life could develop in such an exotic environment. He said that there are two possible barriers to human habitability: excessive UV radiation and a lack of nutrients needed to sustain or form life.
The Hycean worlds are fortunate to exist in a larger habitable zone than they were used to. This is also known as the Goldilocks Zone, which is the area of a star system where liquid water can exist at its surface.
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Madhusudhan explained that a Hycean planet can be far away from the star and still be habitable. The planet can also be closer to the star than an Earthlike planet, and still be habitable. Because of the Hycean worlds' hydrogen-rich atmosphere and their higher surface temperatures than planets similar to Earth, this is possible.
Astrobiologists will find the new paper of great interest. The existence of Hycean worlds in the Milky Way is very common, which suggests that there may be more habitable exoplanets than we thought. Researchers also gave a list of trace biosignatures scientists should look for when studying these exoplanets. These include oxygen, methane and nitrous oxide as well as rare gases like dimethyl sulphide and methyl chloride. While not indicative of life on Earth, they could indicate life on Hycean planets.
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The team identified 11 potential Hycean worlds that orbit nearby starsall red dwarfs, which are promising targets for biosignature research. Madhusudhan said that K2-18b is the most promising, and we have already made observations with the James Webb Space Telescope.
The James Webb space telescope (JWST) will provide a great tool to study K2-18b, and other mini-Neptunes that are Hyceans. After many years of delay, the next-generation telescope will launch later in the year.
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This paper's hypothesis is testable. If spectroscopic scans on Hycean worlds show no trace of the proposed biosignatures it is likely that this indicates that these exoplanets may be dead and inhospitable. However, if these biosignatures are detected in our observations, it would be a completely different story and a very exciting result.
