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Home / Science / Water vapor – and maybe even rain – can be found on a distant world twice the size of the earth

Water vapor – and maybe even rain – can be found on a distant world twice the size of the earth

Water vapor was found in the atmosphere of a distant planet just over twice the size of the Earth. It is the smallest world ever with water in the surrounding atmosphere, and it is possible that it even rains there liquid water. This makes this world a tempting candidate for the constant search for extraterrestrial life outside of our cosmic neighborhood.

It is particularly exciting for scientists to find water around an exoplanet (a world outside our solar system) because water is an important ingredient in our planet's life. It could be just as vital to life that exists elsewhere in the universe. Researchers have found this precious molecule earlier on exoplanets, but these worlds were not the places where life could thrive. They were big gas balls of similar size as Jupiter or Neptune, lacking any surface for life as we know it.

This something more unique is the planet described in a study submitted to the Astronomical Journal and published on arXiv last night , The name K2-1

8b is about nine times as massive as our own Earth, a kind of world often referred to as Mini Neptune. Worlds of this size are abundant in our galaxy, but they lack our own solar system. K2-18b also orbits a sweet spot around its host star, known as a habitable zone, where the surface of a planet can collect exactly the water that has the right temperatures. This means that this planet shares some very important features with our planet. "For the first time, with a planet in this temperature range – an area very similar to Earth – we are showing that there is indeed liquid water," explains Björn Benneke, exoplanet researcher at the University of Montreal and lead author of the ArXiv published study, telling The Verge .

Although it is a big deal for exoplanet explorers to find water, it is unlikely that this world is flooded in oceans. In fact, it seems unlikely that the surface of the planet is rocky due to its size. "These planets will not look like the Earth," says Sara Seager, an exoplanet expert and MIT professor not involved in this research The Verge. "It's definitely not rocky, as we know a rocky planet." K2-18b also orbits a star that is very different from our Sun. Overall, these factors significantly reduce the chances of survival.

Researchers found K2-18b for the first time thanks to NASA's Kepler Space Telescope, a spacecraft that was nearly 100 million miles from Earth and was looking for exoplanets in the last decade. Whenever an exoplanet passes directly between its parent star and the earth, the light of the star is slightly dimmed. This is a tiny change Kepler could see. In observing this transit, Kepler discovered more than 2,000 exoplanets. In 2015, the spaceship K2-18b, located 111 light-years from Earth, intercepted.

NASA's Hubble Space Telescope.
Image: NASA.

Then Benneke and his team used in 2016 and 2017 NASA's Hubble Space Telescope is currently in orbit around Earth to learn more about the atmosphere of K2-18b. The chemicals and molecules that surround an exoplanet can tell us a lot about what might lurk on the surface of the distant world. For example, the substantial amounts of methane in the earth's atmosphere are a by-product of the many biological organisms living here.

Investigating the atmosphere of an exoplanet is especially difficult for earth-like worlds. The light of these distant space rocks is easily overwhelmed by the light from their parent stars, making them incredibly hard to see. And to find out what's in the atmosphere of an exoplanet, researchers must observe the light of the star as it filters through the "outer edges" of the world. When the light flows through the gas, it is slightly warped, indicating the type of molecules present. It is an incredibly delicate – and challenging – measurement.

Researchers were lucky with K2-18b because it has an atmosphere that extends far into space, making it a bit easier to observe. "It's a bit like a hybrid planet that may have a rocky ice core, but most of its volume is actually gas," says Benneke. It also orbits a kind of faint little star known as the Red Dwarf, which is not as bright as a star like our Sun. This makes it easier to study planets that could circle nearby.

Benneke and his team watched the planet during its eight-fold transition to detect water vapor in the atmosphere. Then they made some climate models and found that the vapor is likely to form clouds in which water condenses and then rains down on the planet – just like on Earth. "When you talk to a biologist, the steam does not interest him, they take care of liquid water," says Benneke, "because biology only works if you have liquid water."

Yet, we do not know much about this planet, Seager notes that exoplanets believed to be rocky like Earth, Venus, or Mars are typically less than 1.6 times the size of our planet, which is 2.3 times as big as the earth, which means the surface is most likely not rocky. "It's way above that threshold," says Seager, who is either a rocky core surrounded by a huge shell of atmosphere or it is possible that half of it is made of water ice, both of which are not very conducive to oceans with water on rocky ground like here on Earth. "These objects, the mini-neptune are extremely widespread and we do not know what they are, "says Seager.

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