K2-18b

A far world orbits a small star. This world is much bigger than Earth. It might have a giant ocean of water. The air around it has water in it. It also has other gases.

K2-18b is a far-off world. It orbits a small, red star. This star is called K2-18. The star is in the constellation Leo. K2-18b is much larger than Earth. It is a sub-Neptune. This means it is bigger than Earth but smaller than Neptune. It is about 2.6 times wider than our home.

Scientists use big tools to study it. The James Webb Space Telescope looked at its air. This air is called an atmosphere. The telescope found methane and carbon dioxide. It also found water vapour.

In 2025, some people reported finding a chemical called dimethyl sulfide. On Earth, this chemical comes from life. However, scientists are not sure yet. They do not know if it is real. They do not know if life lives there. The planet stays in a habitable zone. This is a place where it might be warm enough for life.

K2-18b is a fascinating world located far away from Earth. It orbits a small, red star named K2-18 in the constellation Leo. This star is an M dwarf, which means it is smaller and colder than our Sun. K2-18b is a sub-Neptune planet with a radius about 2.6 times larger than Earth. It sits in the habitable zone of its star. This is the area where temperatures might allow liquid water to exist.

Scientists study this planet by looking at its atmosphere, which is the layer of gases surrounding it. When the planet passes in front of its star, we can see how the starlight changes. The James Webb Space Telescope (JWST) has been used to study these changes. This tool helped find methane and carbon dioxide in the atmosphere. It also found hints of water vapour. Some scientists think these gases suggest a special kind of world. They call these "hycean" planets, which have huge oceans under a layer of hydrogen gas.

We have learned more about K2-18b through many years of space study. It was first found using the Kepler space telescope. Later, the JWST provided much more detail about its chemical makeup. In 2025, researchers reported a possible discovery of a chemical called dimethyl sulfide. On Earth, this chemical is often made by living things. However, this finding is still a matter of debate among scientists. They are not yet sure if the signal is real or if it comes from other processes.

There are many specific facts about this distant system. The star K2-18 is about 2.4 billion years old. K2-18b takes 33 days to complete one orbit around its star. The atmosphere of the planet makes up at most 6.2% of its total mass. Its density is somewhere between the density of Earth and Neptune. Another planet, named K2-18c, also orbits inside the path of K2-18b. This extra planet might even pull on K2-18b using gravity through tides.

Thinking about K2-18b helps us understand how different worlds can be. It is much more like the ice giants Uranus or Neptune than our own Earth. Even though it is different, it receives a similar amount of light as Earth does from the Sun. This makes it a great place to practice finding life elsewhere. We use computer models to imagine its weather and winds. These models help us wonder if a real ocean could hide beneath its thick, hydrogen-rich clouds.

K2-18b is a distant exoplanet that orbits a red dwarf star named K2-18. Located in the constellation Leo, this world is classified as a sub-Neptune. This means it is larger than Earth but smaller than the gas giants in our solar system. K2-18b has a radius about 2.6 times that of Earth. It is a significant subject for astronomers because it orbits within its star's habitable zone. This is the region where temperatures might allow liquid water to exist on a planet's surface.

Scientists study the planet's atmosphere using a method called spectroscopy. When K2-18b passes in front of its host star, starlight filters through the planet's outer gases. By analyzing this light, the James Webb Space Telescope (JWST) can identify specific chemicals. These observations have revealed methane and carbon dioxide in the atmosphere. The JWST also found evidence of water vapour, though its exact concentration is debated. These chemical signatures help scientists build models of what the planet might actually look like.

There are different theories about the composition of K2-18b. Some researchers suggest it is a hycean planet. A hycean planet is a theoretical type of world that features a massive liquid water ocean underneath a hydrogen-rich atmosphere. Others believe it might be a mini-Neptune, which is a gas-rich planet similar to Neptune. The planet's density is intermediate between Earth and Neptune. This density suggests it possesses a thick envelope of hydrogen gas.

The discovery of K2-18b involved several major space missions. It was initially discovered using the Kepler space telescope. Later, the JWST provided much deeper data regarding its chemical makeup. In 2025, a controversial report suggested the presence of dimethyl sulfide (DMS). On Earth, DMS is a chemical produced by life. However, scientists are not yet certain if this signal is a real discovery. It could be caused by non-living chemical processes or measurement errors.

K2-18b exists in a complex stellar system. Its host star, K2-18, is an M dwarf star. This star is smaller and colder than our Sun, with a radius only 45% as large. The star is approximately 2.4 billion years old. K2-18b completes one full orbit around its star every 33 days. There is also another planet, K2-18c, located inside the orbit of K2-18b. This inner planet may interact with K2-18b through tidal forces.

Understanding the climate of K2-18b requires advanced computer simulations. These models look at how winds and temperatures move across the planet. Some models suggest the planet might be tidally locked. This means one side always faces the star while the other remains in darkness. In such a scenario, winds might carry air from the day side to the night side. Models also explore the possibility of clouds. These clouds could be made of water, or even chemicals like ammonium chloride and sodium sulfide.

K2-18b serves as a vital link in our study of planetary evolution. It helps scientists understand the "radius valley," a phenomenon where certain planet sizes are unexpectedly rare. This occurs because planets may struggle to hold onto their atmospheres against stellar radiation. The high-energy X-rays and UV radiation from the M dwarf star can drive atmospheric escape. This process creates an exosphere of hydrogen that slowly leaks into space. Studying K2-18b helps us learn how planets change over billions of years.