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The extreme gravity would make walking impossible, and the sunlight is so fierce that developing cancer would be inevitable. Yet planet K2-18b, which lies 110 light years away in the constellation Leo, is the first world ever discovered which could realistically support alien life.
In a groundbreaking breakthrough, scientists at University College London (UCL) have found that the rocky planet contains liquid water and has an atmosphere, raising the first real hope of finding living extra-terrestrial organisms somewhere other than Earth.
Water was detected by measuring light waves filtering through hydrogen molecules in the planet’s atmosphere, in archived data captured by the Nasa’s Hubble Space Telescope in 2016 and 2017.
Although Hubble did not carry any instruments capable of spotting signs of life - such as methane - new telescopes will soon be launched which can hunt for biosignatures, and may finally answer the question of whether we are alone in the universe.
Dr Angelos Tsiaras, of UCL’s Centre for Space Exochemistry Data, said: “Finding water in a potentially habitable world other than Earth is incredibly exciting.
“This is the only planet we know outside of Solar System that has the correct temperature for liquid water, making it the best candidate for habitability that we know right now.
“This study marks a new era in exoplanet research, crucial to ultimately place the Earth, our only home, into the greater picture of the Cosmos. It brings us closer to answering the fundamental question: Is the Earth unique?”
The planet was first discovered in 2015 by Nasa’s Kepler mission which was looking for worlds in the so-called ‘Goldilocks Zone’, where the temperature is neither too hot or too cold for liquid water.
Water and an atmosphere are now thought to be crucial for life, so much so that scientists no longer think living organisms will be found on Mars, which was stripped of its atmosphere and water billions of years ago.
In constant, K2-18b is wet and warm enough for life to have evolved. It is around twice the size of Earth and eight times the mass, orbiting a highly-active red dwarf star. Although its star is far cooler than our Sun, the planet is much closer to the star, so has a temperature range similar to Earth.
It orbits the star every 33 days, meaning one year on the planet is roughly the equivalent of a month on Earth.
Dr Ingo Waldmann, of UCL, said: “We know how one world that is habitable, our own. We are hoping this is one of many ‘Super-Earths’ that might also be habitable.
“We don’t really know what it’s like down there. It could be a waterworld, the surface could be quite wet, or we may have an entirely dry surface.
“But it will certainly have a high surface gravity so it would be hard to walk on, and if you looked up you would see a red star rather than our orangey-yellow Sun.
“There is higher UV radiation on the surface and for life on Earth that would be bad, as we we would all get cancer.
“Maybe this is not quite your vacation destination just yet, but life may have evolved differently there.”
Even if the surface was more hospitable, visiting or setting up a colony there is impossible. The planet is is 660 trillion miles away and would take 3.7 million years to get there travelling at 20,000 mph.
Data from the planet have been available for several years, but the UCL team developed specialist software to re-examine the wavelengths of light, looking for signs of water.
The technique is called ‘transit spectroscopy’ and takes advantage of the fact that when a planet passes in front of its host star a small chunk of light is filtered through its atmosphere, leaving a footprint of the chemicals in that atmosphere.
The next generation of space telescopes, including Nasa and the European Space Agency’s (ESA) James Webb Space Telescope and ESA’s ARIEL mission carry will advanced instruments that detect even more molecules, and could finally answer whether life is present.
Co-author Professor Giovanna Tinetti, of UCL, and Principal Investigator for ARIEL, said: “Our discovery makes K2-18b one of the most interesting targets for future study.
“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.”
The research was funded by the government’s Science Technology Funding Council (STFC)
Dr Colin Vincent, Head of STFC’s Astronomy Division, said: “Finding other planets that might have the capability to support life is one of the holy grails of the astronomy community.
“This result based on Hubble data gives an exciting taste of what may be possible in the next few years as a number of new telescopes and space missions come online.”
Secretary of State Andrea Leadsom added: “Space exploration is one of the greatest adventures of our time, and for decades, scientists and astronomers have scoured the skies for planets capable of supporting life.
“This discovery by UK researchers is a giant leap forward in this endeavour, opening a new world of possibilities.
“The secrets of our universe are out there, and I am enormously proud that our Government-backed researchers and councils are at the forefront of efforts to unlock answers to mysteries that have endured for centuries.”
The discovery was published in the journal Nature Astronomy.