Water discovered in the atmosphere of an exoplanet in the habitable zone. It could be rain

Astronomers using the Hubble Space Telescope have discovered water in the atmosphere of an exoplanet located in the habitable zone of its star. If confirmed, this will be the first time we detect water – an essential ingredient of life as we know it – on an exoplanet. Water has been detected as vapor in the atmosphere, but the temperature of the planet means that it could maintain liquid water on the surface, if it is rocky.

The planet is called K2-18b and is about 110 light-years away. The planet is very different from the Earth. It is a super-earth, twice as big as Earth and about eight times more massive. K2-18b is orbiting a red dwarf star and was discovered in 2015 by the Kepler Space Telescope.

Astronomers from the Center for Space Exochemistry, data from University College London in the UK, have discovered data from the Hubble Space Telescope's wide-field camera 3. Their findings appear in an article entitled "Water vapor in the atmosphere of the habitable zone planet K2-18b", published in Nature Astronomy.The detection is based on the spectroscopic signature of the water in the atmosphere of the exoplanet.

Dr. Angelos Tsiaras (CSED), its lead author, said in a press release, "Finding water on a potentially habitable world other than Earth is incredibly exciting. K2-18b is not "Earth 2.0" because it is much heavier and has a different atmospheric composition. However, this brings us closer to the answer to the fundamental question: is the Earth unique?

The team behind the discovery developed algorithms and managed the Hubble archived data from 2016 to 2017. They analyzed the light of the stars of the red dwarf as it crossed the atmosphere of the exoplanet. They discovered the molecular signature of water, as well as hydrogen and helium.

These results have yet to be confirmed, but if and when they are, the implications are intriguing. Scientists believe that super-lands like this are the most common type of planet in the Milky Way. And red dwarf stars like the K2-18b orbits are the most common type of star. They are also the coolest and most durable, while being the smallest. This indicates that there could be many more exoplanets similar to this one.

Kepler has discovered hundreds of Super-Earths, which are planets whose masses lie between Earth and Neptune, and NASA's TESS is expected to find hundreds more. According to the co-author of this new article, Dr. Ingo Waldmann, this bodes well for the search for potentially habitable exoplanets.

In a press release, Dr. Waldmann said, "With so many new super-Earths expected to be discovered over the next two decades, it is likely to be the first discovery of many potentially habitable planets. This is not only because the super-lands like K2-18b are the most common planets of our Milky Way, but also because the red dwarfs, stars smaller than our Sun, are the stars most common. "

The planet has a very short year. It only takes 33 days to complete an orbit. The researchers think that K2-18b is a rocky or icy planet. If it is icy, it can hold a lot of water inside. But these are just preliminary results.

According to the authors, the atmosphere could also contain nitrogen and methane, two chemicals associated with life. But unfortunately, they were unable to detect them. This will have to wait for further studies, which will also allow them to estimate the cloud cover and the percentage of water in the atmosphere.

K2-12b is really close to its star, but since red dwarfs are not as energetic as our Sun, the exoplanet receives about as much energy as Earth sends from our Sun. Astronomers' calculations show that its temperature is similar to that of Earth: somewhere in the range of about 72 ° C to 47 ° C (-99 to 116 ° F).

These are exciting results, but the prospects for life on this exoplanet are not fantastic. Although the planet itself is in the habitable zone of the star, the star it orbits is perhaps not very hospitable. Red dwarfs can emit a lot of flares and all this energy can significantly limit the potential for survival.

On the other hand, the fact that K2-12b has an atmosphere is exciting, all the more so as it contains a lot of hydrogen. An atmosphere can protect a planet from the radiation of a star, just as the Earth does. If the atmosphere of the planet is dominated by hydrogen, which is very light and easily dissipated by stellar radiation, it is an indication that, in a certain way, the K2-12b could be protected, even if he turns around a red dwarf.

The size of K2-12b and other super-terrestrial is also a factor in favor of habitability. "The water can stay long enough because the superlands can keep their atmosphere longer, because they have a greater gravity," said Giovanna Tinetti, a physicist who co-wrote the paper, in an appeal to the press.

"This study contributes to our understanding of habitable worlds beyond our solar system and marks a new era for exoplanet research, crucial for placing the Earth, our only home, in the big picture of the Cosmos," he said. Dr. Tsiaras.

This discovery requires follow-up observations to confirm it. We also need better telescopes to study its atmosphere in more detail and that of other exoplanets. Two telescopes in the horizon will tackle this problem. The James Webb Space Telescope will have the powerful ability to examine the atmosphere of the exoplanets, which is really the next step in understanding all the exoplanets discovered by Kepler and that will be by TESS.

ESA's ARIEL mission (a major investigation into infrared infrared exoplanets with remote sensing) will be launched in 2028 and will study in detail the atmospheres of about 1000 exoplanets. ARIEL and JWST will give us a much better understanding of K2-12b and similar exoplanets.

Professor Giovanna Tinetti (UCL CSED), co-author and lead researcher for ARIEL, said: "Our discovery makes K2-18b one of the most interesting targets for future studies. More than 4000 exoplanets have been detected, but we know little about their composition and their nature. By observing a large sample of planets, we hope to reveal secrets about their chemistry, their formation and their evolution. "

"Understanding how habitability evolves in a hydrogen-rich atmosphere will become a very intense subject of study over the next 10 years," Waldmann said.

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