Large rocky exoplanet 'could have right conditions to sustain life'

Large rocky planet 124 light years away from Earth appears to be covered in WATER and ‘could have right conditions to sustain alien life’

  • The planet is about twice the size of the Earth with possible lakes and vast seas
  • Researchers predict they will know whether it has signs of life within the decade 
  • Large amounts of water vapour have been discovered encircling the planet
  • It has been called K2-18b by astronomers who plan to study it in more detail when the James Webb Space Telescope comes online

A large rocky planet twice the size of the Earth has been discovered orbiting inside its star’s habitable zone and could have the right conditions to sustain alien life.

The exoplanet, called K2-18b, is 124 light years away appears to be covered in water, according to researchers from Cambridge University.

While they can’t tell whether there is life on the planet now, by the end of the decade scientists think new telescopes will be able to spot the gases made by alien species.

Computer models suggest an ocean world – with liquid water below the atmosphere at pressures and temperatures similar to those found in our seas.

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Artist’s impression of K2-18b with its potentially vast oceans and lakes across the ‘waterworld’ planet – it may contain signs of life

Last autumn two different teams of astronomers detected water vapour encircling the exoplanet and new analysis hints at a life supporting ecosystem.

The Cambridge team confirmed the atmosphere is hydrogen-rich with a significant amount of water vapour but levels of other chemicals such as methane and ammonia were lower than expected.

The next generation of space telescopes being launched this decade will be able to investigate if this is down to biological processes.

If the lower levels of methane and ammonia are due to biological processes then it is likely that planet contains active life of one form or another. 

Lead author Dr Nikku Madhusudhan said water vapour has been detected in the atmosphere of a number of exoplanets studied so far.

‘Even if the planet is in the habitable zone, that doesn’t necessarily mean there are habitable conditions on the surface,’ Madhusudhan said.

‘To establish the prospects for habitability, it’s 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.’

The researchers determined the composition and structure of both the atmosphere and interior for the first time using existing observations.

They used detailed numerical and statistical models and took into account its radius and mass. These are 2.6 and 8.6 times greater than Earth’s, respectively.

K2-18b is in a planet category known as a ‘super Earth’ – and has a temperature cool enough to have liquid water, between 32F and 104F – similar to Earth.

Given its size it’s been suggested it’s more like a small Neptune than a large Earth.

This is likely to cause it to have a significant hydrogen ‘envelope’ surrounding a layer of high-pressure water – with an inner core of rock and iron.

If the hydrogen envelope is too thick, the temperature and pressure at the surface of the water layer beneath would be far too great to support life.

However, the latest findings, published in The Astrophysical Journal Letters, show that is not the case and it is more likely closer to Earth’s atmosphere.

Co-author Matthew Nixon said: ‘We wanted to know the thickness of the hydrogen envelope – how deep the hydrogen goes.

‘While this is a question with multiple solutions, we’ve shown you don’t need much hydrogen to explain all the observations together.’

The James Webb Space Telescope is due to launch in 2021 and will help astronomers discover the conditions on exoplanets and possibly find signs of life

The researchers found the maximum extent of the hydrogen envelope allowed by the data is around six per cent of the planet’s mass.

The minimum amount of hydrogen is similar to the Earth’s atmosphere.

In particular a ‘number of scenarios allow for an ocean world,’ said the researchers.

The study will also enable the search for habitable conditions and signs of life on planets outside the solar system that are much bigger than Earth.

Additionally, planets such as K2-18b are more accessible to atmospheric observations with current and future facilities.

The techniques used by the Cambridge experts can be refined further by using future observations from NASA’s James Webb Space Telescope.

The much anticipated space-based observatory is being launched next year to accelerate the search for alien life.

The findings have been published in the Astrophysical Journal Letters. 


Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere. 

To understand these new world’s, and what they are made of, scientists need to be able to detect what their atmospheres consist of.  

They often do this by using a telescope similar to Nasa’s Hubble Telescope.

These enormous satellites scan the sky and lock on to exoplanets that Nasa think may be of interest. 

Here, the sensors on board perform different forms of analysis. 

One of the most important and useful is called absorption spectroscopy. 

This form of analysis measures the light that is coming out of a planet’s atmosphere. 

Every gas absorbs a slightly different wavelength of light, and when this happens a black line appears on a complete spectrum. 

These lines correspond to a very specific molecule, which indicates it’s presence on the planet. 

They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.

By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up the atmosphere of a planet. 

The key is that what is missing, provides the clues to find out what is present.  

It is vitally important that this is done by space telescopes, as the atmosphere of Earth would then interfere. 

Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study the light before it has had chance to reach Earth. 

This is often used to look for helium, sodium and even oxygen in alien atmospheres.  

This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium 

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