Scientists have found that a planet more than twice as big as Earth could be habitable, opening up new possibilities in the search for life on other planets.
The new discovery suggests that alien life could flourish on worlds bigger than Earth but smaller than Neptune, just like the exoplanet K2-18b.
Researchers looked at the mass, radius and atmospheric data of the distant exoplanet and used models to find that it is possible the planet could have liquid water, in habitable conditions, underneath the hydrogen-rich atmosphere on its surface.
The exoplanet is found 124 lightyears away, relatively close by in terms of exoplanets. It is also relatively similar to Earth: with a radius 2.6 times as big as our planet’s and a mass 8.6 times Earth’s.
The world known as K2-18b is also already somewhat famous. It was discovered in 2017, prompting frenzied speculation about what conditions might be like there, and was the subject of even more excitement towards the end of last year, when it was the first ever potentially habitable planet found to have water vapour in its atmosphere.
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Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas flom fledgling stars buried within, was captured by Nasa’s Hubble Space Telelscope in February 2010
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The first ever selfie taken on an alien planet, captured by Nasa’s Curiosity Rover in the early days of its mission to explore Mars in 2012
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Death of a star: This image from Nasa’s Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy
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Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa’s New Horizons spaceraft at a distance of 4.1 billion miles from Earth
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An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust
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The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth
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Pluto, as pictured by Nasa’s New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015
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A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun
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Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand
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Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015
Nasa/Scott Kelly
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Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas flom fledgling stars buried within, was captured by Nasa’s Hubble Space Telelscope in February 2010
Nasa/ESA/STScI
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The first ever selfie taken on an alien planet, captured by Nasa’s Curiosity Rover in the early days of its mission to explore Mars in 2012
Nasa/JPL-Caltech/MSSS
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Death of a star: This image from Nasa’s Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy
Nasa
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Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa’s New Horizons spaceraft at a distance of 4.1 billion miles from Earth
Getty
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An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust
Nasa
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The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth
Getty
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Pluto, as pictured by Nasa’s New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015
Nasa/APL/SwRI
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A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun
Nasa
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Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand
Nasa/JPL/University of Arizona
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Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015
Nasa/Scott Kelly
The new study gives the first look at what conditions could be like underneath that atmosphere, however. And it suggests that they could be habitable in just the way scientists had hoped.
Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the study, said: “Water vapour has been detected in the atmospheres of a number of exoplanets but, even if the planet is in the habitable zone, that doesn’t necessarily mean there are habitable conditions on the surface.
“To establish the prospects for habitability, it is important to obtain a unified understanding of the interior and atmospheric conditions on the planet – in particular, whether liquid water can exist beneath the atmosphere.”
Because of the size of K2-18b, some suggest it would be more like a smaller version of Neptune than a larger version of Earth.
It is thought a mini-Neptune would have a significant hydrogen envelope surrounding a layer of high-pressure water, with an inner core of rock and iron.
If this envelope is too thick, it would be too hot, and pressure at the surface of the water layer beneath would be far too great to support life.
According to the new study published in The Astrophysical Journal Letters, despite the size of K2-18b, its hydrogen envelope is not necessarily too thick and the water layer could support life.
Astronomers used the existing observations of the atmosphere, to confirm the atmosphere is hydrogen-rich with a significant amount of water vapour.
They also found that levels of other chemicals such as methane and ammonia were lower than expected.
But whether these levels can be attributed to biological processes remains to be seen.
The researchers found that the maximum extent of the hydrogen envelope allowed by the data is around 6% of the planet’s mass, though most of the solutions require much less.
The minimum amount of hydrogen is about one-millionth by mass, similar to the mass fraction of the Earth’s atmosphere.
Additional reporting by agencies
