Water detected in atmosphere of potentially habitable super-Earth

For the first time, astronomers have peered into the atmosphere of an exoplanet – a planet outside our solar system – and discovered both water vapor and temperatures that could potentially support life, according to a new study.

The exoplanet, known as K2-18b, is eight times the mass of Earth and known as a super-Earth, or exoplanets between the mass of Earth and Neptune. It orbits a red dwarf star 110 light-years away from Earth in the Leo constellation. The planet was first discovered in 2015 by NASA’s Kepler spacecraft.

An artists's conception shows planet LP 791-18d. The volcanically active planet, which is a similar size to Earth, was discovered by NASA's Spitzer Space Telescope.

This artist's illustration depicts the rocky exoplanet GJ 486 b, which orbits a red dwarf star located 26 light-years away from Earth. Astronomers have detected hints of water vapor in the system, but they can't be sure if it signifies a planetary atmosphere or if it's part of the star.

This illustration shows an Earth-size exoplanet called TOI 700 e, discovered orbiting the small, cool M dwarf star TOI 700, which is located 100 light-years away. Its other Earth-size sibling, TOI 700 d, can be seen in the distance.

TOI 700 d is the first potentially habitable Earth-size planet spotted by NASA's planet-hunting TESS mission.

Artist's impression of the exoplanet WASP-121 b. It belongs to the class of hot Jupiters. Due to its proximity to the central star, the planet's rotation is tidally locked to its orbit around it. As a result, one of WASP-121 b's hemispheres always faces the star, heating it to temperatures of up to 3000 degrees Celsius. The night side is always oriented towards cold space, which is why it is 1500 degrees Celsius cooler there.

This artist's impression shows a close-up view of Proxima d, a planet candidate recently found orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The planet is believed to be rocky and to have a mass about a quarter that of Earth. Two other planets known to orbit Proxima Centauri are visible in the image too: Proxima b, a planet with about the same mass as Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

The discovery of a second exomoon candidate hints at the possibility that exomoons may be as common as exoplanets.

This artist's impression shows the football-shaped planet WASP-103b (left) closely orbiting its host star.

This image shows double-star system b Centauri and its giant planet b Centauri b. The star pair is the bright object at top left. The planet is visible as a bright dot in the lower right. The other bright dot (top right) is a background star.

This artist's rendering shows a Jupiter-like planet orbiting a dead white dwarf star 6,500 light-years away from Earth. The planet survived the violent phases of stellar evolution leading to the star's death.

This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky.

Astronomers have identified a new class of habitable planets, which they call Hycean planets. These are hot, ocean-covered planets with hydrogen-rich atmospheres.

This artist's illustration shows L 98-59b, one of the planets in a planetary system 35 light-years away from Earth. This planet has half the mass of Venus.

In this artist's illustration, two gaseous exoplanets can be seen orbiting the bright sun-like star HD 152843.

An artist's rendering of TOI-1231 b, a Neptune-like planet about 90 light years away from Earth.

This artist's conception depicts a violent flare erupting on the star Proxima Centauri as seen from the viewpoint of a planet orbiting the star called Proxima Centauri b.

After losing its gaseous envelope, the Earth-size core of an exoplanet formed a second atmosphere. It's a toxic blend of hydrogen, methane, and hydrogen cyanide that is likely fueled by volcanic activity occurring beneath a thin crust, leading to its cracked appearance.

This illustration shows the metaphorical measuring of the density of each of the seven planets in the nearby TRAPPIST-1 system. New measurements have revealed the most precise densities yet for these planets and they're very similar -- which means they also likely have similar compositions.

This artist's illustration shows the view from the furthest planet in the TOI-178 system.

This artist's illustration shows TOI-561b, one of the oldest and most metal-poor planetary systems discovered yet in the Milky Way galaxy. Astronomers found a super-Earth and two other planets orbiting the star.

This massive and distant exoplanet, called HD106906 b, has an elongated and angled orbit that causes it to take 15,000 Earth years to complete one lap around its twin stars.

This is an artist's impression of a free-floating rogue planet being detected in our Milky Way galaxy using a technique called microlensing. Microlensing occurs when an object in space can warp space-time.

This is an artist's impression of exoplanet WASP-189 b orbiting its host star. The star appears to glow blue because it's more than 2,000 degrees hotter than our sun. The planet, which is slightly larger than Jupiter, has a tilted orbit around the star's poles rather than its equator.

For the first time, an exoplanet has been found orbiting a dead star known as a white dwarf. In this artist's illustration, the Jupiter-sized planet WD 1856 b orbits the white dwarf every day and a half.

This illustration shows a carbon-rich planet with diamond and silica as ts main minerals. Water can convert a carbon-rich planet into one that's made of diamonds. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be made of an iron-carbon alloy.

This image shows a young sun-like star being orbited by two gas giant exoplanets. It was taken by the SPHERE instrument on European Southern Observatory's Very Large Telescope. The star can be seen in the top left corner, and the planets are the two bright dots.

This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star.

This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887.

The newly discovered exoplanet AU Mic b is about the size of Neptune.

This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth.

This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures.

This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away.

Weird and wonderful planets beyond our solar system

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A research team used archival data collected by the Hubble Space Telescope between 2016 and 2017 that captured starlight as it passed through the atmosphere of the exoplanet. The researchers said they clearly saw the signature for water vapor in the atmosphere when they put the data through algorithms. They also observed the signatures of hydrogen and helium in the atmosphere, two of the most abundant elements in the universe.

The detection of water vapor in the atmosphere of this exoplanet is particularly exciting to the researchers because the exoplanet also lies within the habitable zone of its star, which includes the right temperatures for liquid water to exist on the surface of the planet and potentially support life as we understand it.

Artist's composition of a volcanic exo-Io undergoing extreme mass loss. The hidden exomoon is enshrouded in an irradiated gas cloud shining in bright orange-yellow, as would be seen with a sodium filter. Patches of sodium clouds are seen to trail the lunar orbit, possibly driven by the gas giant's magnetosphere. CREDIT ? University of Bern, Illustration: Thibaut Roger

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The researchers published their findings in the journal Nature Astronomy on Wednesday.

“Finding water in a potentially habitable world other than Earth is incredibly exciting,” said Angelos Tsiaras, study author and research associate at the University College London’s Centre for Space Exochemistry Data. “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?”

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The exoplanet completes one orbit around its star every 33 days and it’s much closer to its star than Earth is to the sun. But the red dwarf star is also much cooler than our sun. Based on the researchers’ calculations, they believe the planet could even be at a similar temperature to that of Earth. But the range extends to include temperatures much colder or warmer than Earth because of the constraints of their data.

The red dwarf star is an active one, however, which is likely exposing the exoplanet to more radiation than Earth receives.

“With so many new super-Earths expected to be found over the next couple of decades, it is likely that this is the first discovery of many potentially habitable planets,” said Ingo Waldmann, study co-author and lecturer in extrasolar planets at the University College London’s Centre for Space Exochemistry Data. “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.”

Trappist-1 system

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The Hubble Space Telescope is only sensitive to the signature of water, but future telescopes like the James Webb Space Telescope and the European Space Agency’s ARIEL mission will be able to study exoplanet atmospheres in greater detail with more advanced instruments.

The researchers believe that other elements like nitrogen and methane could also be present in the atmosphere, but only future observations by more advanced telescopes will reveal them.

“Our discovery makes K2-18 b one of the most interesting targets for future study,” said Giovanna Tinetti, study co-author and principal investigator for ARIEL. “Over 4,000 exoplanets have been detected but we don’t know much about their composition and nature. By observing a large sample of planets, we hope to reveal secrets about their chemistry, formation and evolution.”