Exoplanet K2-18b has the potential to be an ocean planet with a hydrogen-rich atmosphere. Not only that. There is methane and carbon dioxide on this planet!
Illustration of exoplanet K2-18b and its host star. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
Planet K2-18b. This planet was discovered by the Kepler Telescope in 2015 orbiting a red dwarf star in the constellation Leo. The distance of this system is 120 light years from Earth. Far but close on an astronomical scale.
What is attractive about this exoplanet is that its location is not too far and not too close to its parent star. In short, planet K2-18b is in the star’s habitable zone or the area where water can remain liquid on the planet’s surface. Even though it is at a distance of 0.14 AU, which is much closer than Mercury’s distance to the Sun, K2-18b is still within the star’s habitable zone range. This is because the star K2-1b is a red dwarf star which is also smaller and cooler than the Sun, so its habitable zone is also closer than the Sun. The parent star of this system is only 0.35 solar masses with a temperature of 3457 K.
Discovery of the Webb Telescope
In 2019, the Hubble Telescope discovered traces of water vapor in the planet’s atmosphere as well as the possibility of rain on the planet. Because of this, astronomers then suspect that the planet K2-18b has the potential to have water.
In the latest observations from the James Webb Telescope, the results of observations at infrared wavelengths actually show what is in the atmosphere of planet K2-18b. Astronomers discovered carbon molecules in the planet’s atmosphere. More precisely, they discovered the presence of methane and carbon dioxide which sparked the idea that K2-18b is a Hycean planet or a planet that has the potential to have a hydrogen-rich atmosphere with oceans on the planet’s surface.
The abundance of methane and carbon dioxide and the lack of ammonia discovered by the James Webb Telescope are supporting factors that suggest that an ocean of liquid water might exist beneath a hydrogen-rich atmosphere. And of course it would be interesting if it turned out that life was developing in the water. But of course this is still homework that will only be completed far in the future when our technology can detect water on the surface of exoplanets.
For now, we still suspect that this planet has water under its atmosphere which triggers the formation of carbon dioxide and methane in the upper layers of the atmosphere. However, there are other interesting discoveries from observations by the James Webb Telescope.
Spectrum of exoplanet K2-18b showing the composition of the planet’s atmosphere. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
Astronomers found weak indications of the presence of dimethyl sulfide (DMS) molecules in the spectroscopy results of the James Webb Telescope. This molecule is quite closely related to life. Dimethyl sulfide (DMS) or methylthiomethane molecules, are organic sulfur compounds with the formula (CH3) 2S. On Earth, this compound is produced by phytoplankton and bacteria in the ocean. Because if this DMS compound is in K2-18b then it could be that there is the potential for life on this planet.
However, the conclusion that K2-18b has the potential to have life due to the presence of DMS is still premature. Further observations to confirm the presence of DMS molecules must still be carried out to obtain certainty about the traces of DMS molecules in the planet’s atmosphere.
Is K2-18b Livable?
Exoplanet K2-18b is indeed in the habitable zone and has the potential to be habitable if there is liquid water on its surface. However, we need to analyze various factors to conclude that planet K2-18b is a habitable planet.
Generally, when astronomers look for planets that have the potential to have life, they look for planets like Earth. In this case, the composition, size and mass of the planet being sought are not much different from Earth. Apart from that, the location is also in a stellar habitable area.
In terms of location, K2-18b already meets the requirements. But not with other characteristics. One thing is certain, planet K2-18b is a type of planet that does not exist in the Solar System.
Planet K2-18b is 2.7 times larger and 8.9 times more massive than Earth. The maximum size a planet can have on a rocky surface under a thin atmosphere is only about 1.3 times the size of Earth and twice as massive as Earth.
Not only that. The density of K2-18b is only 2.38 gr/cm3, or only half the density of Earth (5.5 gr/cm3).
Inevitably, K2-18b is not a super-Earth planet but a mini-Neptune planet. If so, then this planet likely has a high-pressure icy interior like Neptune, with a hydrogen atmosphere and oceans on the surface. However, the ocean on K2-18b could be too hot for life or even unable to survive in liquid form.
Another factor that needs to be taken into account is that exoplanet K2-18b is a planet that is gravitationally locked with its host star. Thus, this planet has one side of eternal day and another side that is always dark or eternal night. The implication is that the temperatures on both sides will be very different. On the day side, the planet’s surface will continue to be baked by radiation, while the night side is actually very cold. K2-18b does receive the same heat as Earth. But how heat is distributed to the night side and how life can grow in an environment like this is still a question mark.
Apart from that, the red dwarf star K2-18b also regularly emits bursts of X-rays and ultraviolet rays that can destroy life forming on planets.
So, it looks like K2-18b is still the same. This is not a planet suitable for life as we know it. But if there really is exotic life there, it would certainly be very interesting to study.
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2023-09-28 09:52:07
#Indication #Exoplanet #K218b #Ocean #Planet
