Water Detected On Habitable ‘Super-Earth’ By Astronomers

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A planet just outside our solar system has been discovered by astronomers, and it’s known to have water and temperatures similar to Earth.

It’s the only planet outside our solar system with conditions which could support life, and sits around 110 light years away.

The exoplanet (a planet outside the solar system) has been named K2-18b. It’s eight times the size of Earth, lying in the constellation of Leo in the northern sky, and has been described as the ‘holy grail’ for planet hunters seeking an Earth-like planet with water in its atmosphere. The discovery of water in the atmosphere means life could be found there.

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Speaking about the discovery, first author Dr. Angelos Tsiaras, of University College London’s Centre for Space Exochemistry Data (CSED), said:

Finding water in a potentially habitable world other than Earth is incredibly exciting.

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?

The water vapour found in K2-18b comes from the evaporation of water or ice on the planet, and though vapour has been found on other far away planets, this is the first to be the ideal distance from the solar system’s star to allow life to develop.

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The team, whose findings are reported in Astronomical Journal, say the water’s source could exist in liquid form – a pre-requisite for life.

They combined data from 2016 and 2017 captured by the Hubble Space Telescope with their own algorithms to analyse starlight filtered through the atmosphere.

The results revealed the molecular signature of water vapour, while also indicating the presence of hydrogen and helium, which produces energy.

Other vital molecules, including nitrogen and methane, may also be present but remain undetectable with current observations. Further studies are required to estimate cloud coverage and the percentage of atmospheric water present.

K2-18b was first discovered in 2015, and is one of hundreds of super-Earths – planets with a mass between Earth and Neptune – found by NASA’s Kepler spacecraft. While more ‘super-Earths’ are expected to be uncovered in the coming years, K2-18b is the most promising so far. However, as the planet orbits an active red dwarf, its environment is expected to be more hostile than Earth.

Co-author Dr Ingo Waldmann, also of UCL CSED, said:

With so many new super-Earths expected to be found over the next couple of decades, it’s likely this is the first discovery of many potentially habitable planets.

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.

The next generation of space telescopes, including the NASA/ESA/CSA James Webb Space Telescope and ESA’s ARIEL mission, will be able to characterise atmospheres in more detail as they will carry more advanced instruments.

ARIEL is expected to launch in 2028, and will observe 1,000 planets in detail to get a truly representative picture of what they are like.

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Co-author Prof Giovanna Tinetti, also of UCL CSED 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 team looked for the signal of water absorption in starlight poking through the edges of the atmosphere when the planet passed in front of its star.

Björn Benneke, an exoplanet researcher at the University of Montreal and author of the study, told The Verge:

For the first time, a planet in this temperature regime — a regime that is very, very similar to the Earth — we are demonstrating that there is actually liquid water.

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However, according to exoplanet expert and MIT professor Sara Seager, we shouldn’t expect a mirror image of Earth just yet. She added: ‘These planets are not going to look a thing like Earth. It’s definitely not rocky as we know a rocky planet to be.’

According to Benneke though, climate modelling from the team’s observations found the water vapour is forming into clouds, condensing, and raining down on the planet. And it is this liquid water that is essential to life being a possibility there.

Dr Tsiaras added:

This study contributes to our understanding of habitable worlds beyond our solar system and marks a new era in exoplanet research, crucial to ultimately place the Earth, our only home, into the greater picture of the cosmos.

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Charlie Cocksedge

Charlie Cocksedge is a journalist and sub-editor at UNILAD. He graduated from the University of Manchester with an MA in Creative Writing, where he learnt how to write in the third person, before getting his NCTJ. His work has also appeared in such places as The Guardian, PN Review and the bin.