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k2-18b water discovery

Water discovered on an exoplanet

In a fascinating discovery, astronomers found water in a planet’s atmosphere orbiting a far-flung star outside our solar system with Earth-like temperatures that could sustain life. This exoplanet is almost 110 light-years away from our world, and the discovery of water is rather exciting.

According to the research released in the journal Nature Astronomy, K2-18b is eight times the Earth’s mass. It is now the only exoplanet known to have water and temperatures possibly inhabitable. Unlike other giant exoplanets where atmospheric water has been detected, K2-18b could be rocky and rugged like Earth, Venus, and Mars.

Researchers said the planet orbits the cool dwarf star K2-18, which is in the Leo constellation.

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“Finding water in a potentially habitable world other than Earth is incredibly compelling,” remarked author Angelos Tsiaras from the University College London (UCL) in the UK.

“K2-18b is not’ Earth 2.0′ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?” adds Tsiaras.

K2-18b was discovered in 2015. Since then, it has been researched on, and it was a bit of a tricky exoplanet to explore. We understand this rounds up quite carefully around a red dwarf star named K2-18, completing the round every 33 days. Furthermore, the stellar rates of radiation on the planet are comparable to those on Earth (except for the elevated flare activity typical of red dwarfs).

We also understand that the planet’s size is about twice as large as the earth, and about eight times the mass. Astronomers have even reduced the planet to two kinds. In 2017, a team concluded, either a rocky, atmospheric planet like Earth but more massive, or a world with a mostly watery interior covered by a dense ice shell, like Enceladus or Europa.

Kepler space telescope which used to identify planets using the transit method recognized this planet. This is possible when the star, planet and earth are in the same line. The light coming from the star is monitored and when the planet passes in between star and earth (transit), we can see a dip in star’s light. This can give us a lot of data.

It can also support us in studying the atmosphere of a planet. If the light from the star moves through specific wavelengths, certain gasses can absorb them, thus, creating a range of lines. These can be decided by comparing a spectral star profile with a spectral transit profile.

It isn’t simple, however. Even the first detection of the planet needs extremely delicate instruments to detect starry dips, as well as remarkably faint spectral absorption lines.

Tsiaras and his team used the WFC3 device on the Hubble space telescope. They pictured eight transits of the planet in front of the star, bringing them together to generate a weighted average, thereby producing the planet’s spectral profile.

After this, they had to understand what the spectral star profile conveyed through modeling.

Originally, they ran K2-18b atmosphere models with a range of atmospheric molecules that could produce absorption lines, comprising water (H2O), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and ammonia (NH3).

In the planet’s spectrum, only water could be recognized with confidence. Keeping this in mind, the team developed their analysis, now using water solely as a trace gas.

They then formed the atmosphere by applying three different approaches: cloudless, with water vapor in a hydrogen-helium atmosphere; cloudless, with water vapour, hydrogen-helium, and molecular nitrogen; and then cloudy, with water vapour and hydrogen-helium.

All three simulations produced a statistically notable atmosphere at high-resolution levels, with values so similar they couldn’t quite distinguish the three basic types.

We need a lot more data to confirm things and probably the next-generation space telescopes like James Webb telescope might clarify things

Journal Reference: Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b

About the author: Sai Teja Moderator
Sai Teja is a second-year computer science undergraduate at the University of Hyderabad. With expertise in many modern technologies like Machine Learning, he is also a blogger and has interests in digital marketing and SEO also. He has a dream to build a single internet destination for science and technology enthusiasts

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