A Gas-Rich Mini-Neptune with No Habitable Surface. Exoplanet K2-18b is garnering a lot of attention. James Webb Space Telescope spectroscopy shows it has carbon and methane in its atmosphere. Those results, along with other observations, suggest the planet could be a long-hypothesized ‘Hycean World.’

The exoplanet K2-18b could be a “Hycean World”. This is based on observations from the James Webb Space Telescope, which show that the planet’s atmosphere contains carbon and methane.

A Hycean exoplanet is a planet that could have a hydrogen-rich atmosphere and a surface covered by water oceans. The discovery paper for K2-18b argues that the data can be best explained by a habitable “Hycean” world. This world would consist of a thin atmosphere dominated by H2, overlying a liquid water ocean. 

K2-18b is a gas-rich mini-Neptune with no defined surface. A mini-Neptune is a planet that is less massive than Neptune, but has a thick hydrogen-helium atmosphere, and possibly deep layers of ice, rock, or liquid oceans. 

K2-18b was discovered in 2015 and is 124 light-years from Earth. It has a mass of 8.92 Earths and takes 32.9 days to orbit its star.

Here are some examples of planets that contain carbon and methane:

• K2-18b A super-Earth exoplanet with water and temperatures that could support life. NASA’s Webb telescope discovered methane and carbon dioxide in the atmosphere of K2-18b. 
• Mars and Titan A team led by Michael Mumma of NASA detected methane concentrations in excess of 250 ppbv on Mars and Titan. 
• Saturn The atmosphere of Saturn contains trace amounts of methane and ammonia, along with hydrogen, helium, nitrogen, and oxygen. Methane and carbon dioxide are greenhouse gases, which are gases that accumulate in the Earth’s atmosphere and help maintain a warmer temperature. Other greenhouse gases include nitrous oxide, ozone, chlorofluorocarbons, and water vapor.

No, methane and carbon dioxide are not the most abundant greenhouse gases in the atmosphere. Water vapor is the most abundant greenhouse gas, followed by carbon dioxide. Methane is only found in trace amounts. 

Here are some details about methane and carbon dioxide:

• Methane Methane is the second most abundant anthropogenic greenhouse gas (GHG), accounting for about 16% of global emissions. Methane is more than 28 times as potent as carbon dioxide at trapping heat in the atmosphere. 
• Carbon dioxide Carbon dioxide accounts for about 0.04% of the atmospheric gases. It is the primary anthropogenic greenhouse gas, accounting for 64% of the human contribution to the greenhouse effect in 2019.

Yes, methane’s greenhouse effect is higher than carbon dioxide’s over a 20-year period. Methane is 80 times more potent at warming than carbon dioxide over a 20-year period. However, carbon dioxide has a longer-lasting effect

Methane is responsible for more than 25% of the global warming we are experiencing today. It’s estimated to be contributing about 25% to warming temperatures from climate change. 

Methane concentrations in the atmosphere have more than doubled over the last two centuries, largely due to human-related activities

In September 2023, NASA’s James Webb Space Telescope (JWST) discovered carbon-bearing molecules, including methane and carbon dioxide, in the atmosphere of the exoplanet K2-18 b. K2-18 b is 120 light-years from Earth and orbits the cool dwarf star K2-18. It’s 8.6 times more massive than Earth and may have a surface covered with water oceans

The JWST’s observations of exoplanet atmospheres can provide important clues about the conditions on the planet’s surface and whether it could support life. So far, scientists have detected a variety of gases in the atmospheres of exoplanets, including hydrogen, helium, water vapor, carbon dioxide, and methane

K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. A new investigation with NASA’s James Webb Space Telescope into K2-18 b has revealed the presence of carbon-bearing molecules including methane and carbon dioxide

The James Webb Space Telescope (JWST) can detect gases in the atmosphere of exoplanets by breaking down light into its colors. This allows researchers to identify the characteristic “fingerprints” of different gases and determine the composition of the atmosphere

During transits, a small amount of starlight passes through the exoplanet’s atmosphere before reaching telescopes like Webb. The starlight’s passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet’s atmosphere. 

Different gases absorb different combinations of colors. Researchers can analyze small differences in brightness of the transmitted light across a spectrum of wavelengths to determine exactly what an atmosphere is made of. 

The JWST’s unmatched infrared sensitivity allows it to see objects that emitted light inside a dusty cloud.

K2-18 b is an exoplanet that orbits the cool dwarf star K2-18 in the habitable zone, 120 light-years from Earth. It is 8.6 times as massive as Earth, and recent studies have suggested that its surface could be covered with water oceans. 

The detection of these molecules, along with a shortage of ammonia, is consistent with the presence of an ocean. This discovery adds to previous studies that suggest that K2-18 b could be a Hycean exoplanet

While K2-18 b is in the habitable zone and has carbon-bearing molecules, it’s not guaranteed to be able to support life. Here are some reasons why K2-18 b might not be habitable: 

• Lack of oxygen K2-18 b has oceans, rain, and certain gases, but it lacks oxygen, which makes it uninhabitable for humans. However, life on K2-18 b may have developed differently than on Earth. 
• Mini-Neptune Most scientists classify K2-18 b as a mini-Neptune, which is unlikely to be habitable. Mini-Neptunes are thought to have a thick hydrogen envelope around a layer of high-pressure water, with an inner core of rock and iron. If the envelope is too thick, it would be too hot and the pressure at the surface of the water layer would be too great to support life. 
• Radiation K2-18 b may be more hostile than Earth and is likely to be exposed to more radiation due to the high level of activity of its red dwarf star. 
• Hydrogen atmosphere Planets like Neptune have deep hydrogen atmospheres and no real solid surface. K2-18 b’s vast size suggests an interior dominated by high-pressure ice, similar to Neptune

According to NASA, the abundance of methane and carbon dioxide, and lack of ammonia, suggest that K2-18 b may have a water ocean under a hydrogen-rich atmosphere. 

However, according to Big Think, there’s no water in the upper atmosphere of K2-18 b, where it could be detected using current technologies. 

K2-18 b is classified as a “hycean planet”, which is a type of planet that has both abundant liquid water and a hydrogen envelope

Yes, K2-18 b has gravity. According to The Extrasolar Planets Encyclopaedia, the exoplanet’s gravitational acceleration is 15.6 m/s2, which is almost 1.6 times Earth’s gravity. 

If most of the exoplanet is solid rock and ice, a visitor would feel 37% heavier than they do on Earth. This is because the gravitational force decreases with the square of the distance from a planet’s center. 

Most scientists consider K2-18 b to be a mini-Neptune, with a deep atmosphere of hydrogen and/or helium, and possibly no solid surface at all.

K2-18 b is likely tidally locked to its star, with one hemisphere always facing the star. However, it’s also possible that K2-18 b orbits in a spin-orbit resonance, similar to Mercury. In a spin-orbit resonance, the planet rotates on its axis 2–3 times for every 1–2 orbital revolutions. 

K2-18 b is a super-Earth exoplanet that orbits an M-type star. It completes one orbit every 33 Earth days. Because red dwarfs are dim, their habitable zones are much closer in.

K2-18 b is a super-Earth, which is a planet with a mass between Earth and Neptune. It’s also a sub-Neptune, meaning it’s between the size of Earth and Neptune

K2-18 b is also a transiting exoplanet, which means that astronomers can detect a drop in brightness when it passes in front of its star. 

K2-18 b is located in the constellation Leo, around 120 light-years from Earth. It orbits the red dwarf star K2-18, which is also known as EPIC 201912552. 

K2-18 b is 8.6 times more massive than Earth. It has a bulk density between Earth and Neptune, which suggests that it may have a rocky or icy interior and a hydrogen-rich cover

K2-18 b is 124 light-years (38 pc) away from Earth. It orbits the red dwarf star K2-18, which is also known as EPIC 201912552. 

K2-18 b was discovered in 2015 by the Kepler space telescope. It’s one of the few exoplanets known to have water and an atmosphere

While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life

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