First evidence of water found in atmosphere of planet K2-18b

Federico Mansilla
Setiembre 13, 2019

Astronomers can only see this exoplanet's upper atmosphere, but it's twice the size and has eight times mass than Earth.

Prior to the discovery of K2-18b, the search for an inhabitable planet outside our solar system was feeling a bit futile.

The habitable zone is the region around a star where temperatures are sufficiently benign for water to exist in liquid form on the surface of a planet. If "most planets are born with a large atmosphere of hydrogen and helium that they can't get rid of, it might make it more hard for complex life to develop - we simply don't know enough at this stage", he said. "This is not only because super-Earths like K2-18b are the most common planets in our Galaxy, but also because red dwarfs - stars smaller than our Sun - are the most common stars".

While K2-18b represents a potential to be Earth-like, it also is quite different from the planet that we call home.

What they found suggests that the composition of K2-18b's atmosphere could range from 0.1 percent water vapor (about the proportion in Earth's upper atmosphere) to a whopping 50 percent.

Because light from the K2-18b's star takes a century to reach the Earth, to travel over there would be "impossible", he said.

The other important result here is due to the fact that Neptune-like planets have turned out to be much more common than we might have expected, and we don't have a strong sense of how their composition might vary based on distance from their host stars. "While not a true Earth-analogue due to its size, this bodes well for our exploration of small planets", Josh Lothringer, who studies exoplanet atmospheres at Johns Hopkins University in the USA, said on Twitter.

Angelos Tsiaras, an astronomer at UCL, said the team is focusing its attention on identifying exoplanets with conditions similar to those on Earth.

More news: Hubble's Brand New Image of Saturn

Two research groups announced this week that they've found water vapor in the atmosphere of a planet 110 light-years away in the constellation Leo. The team's analysis of eight of these transits, as well as transits observed by the Kepler and Spitzer space telescopes, will appear in the Astronomical Journal. However, it brings us closer to answering the fundamental question: "Is the Earth unique?" said Tsiaras.

In a tantalizing first, scientists have discovered water at a planet outside our solar system that has temperatures suitable for life. The team behind the find developed new algorithms that analyzed light from the host star as it filtered through the planet's atmosphere.

Further studies are required to estimate cloud coverage and the percentage of atmospheric water present, the researchers said.

The astronomers who comb through data on planetary surveys looking for potentially habitable planets are searching for worlds with certain specific characteristics. The results revealed the molecular signature of water vapor, and also suggest the presence of hydrogen and helium in the planet's atmosphere.

Not quite Earth 2.0 Even though it has water, K2-18b may be hostile to life since it is likely to be exposed to more high-energy radiation.

"This planet is about the same temperature as Earth, but 2.7 times larger".

Co-author Professor Giovanna Tinetti said: "Our discovery makes K2-18b one of the most interesting targets for future study". The James Webb Space Telescope, when it finally comes online, should be well-suited for exploring exoplanets like these.

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