Astronomers could finally show that alien life does exist on a distant planet following observations today. 

Planet K2-18b – which is more than twice as big as Earth and 120 light-years away – sits within the habitable zone of its star in the Leo constellation.  

Scientists said last year they thought they'd detected dimethyl sulphide gas in its atmosphere – a compound that is 'only produced by life'.

Now, to confirm the finding, the James Webb Space Telescope will undertake hours of observations of the planet on Friday.  

However, space fans will have to wait several months for the results to be authenticated and published.

Scientists made an exciting and potentially ground-breaking discovery in the search for alien life - after detecting signs of a gas produced only by living organisms on a distant water planet known as K2-18b (pictured in an artist's impression)

Detection: A gas 'uniquely associated with life' when found on Earth has been discovered in the atmosphere of K2-18 b. The compound dimethyl sulphide was spotted along with large amounts of carbon dioxide and methane (pictured)

Planet K2-18b: Key facts 

Discovered: 2015 

Star: K2-18 

Orbital duration: 33 days

Constellation: Leo 

Mass: 8.6 times that of Earth 

Radius: 2.6 times that of Earth

Investigations of planet K2-18b are being led by Dr Nikku Madhusudhan, an astrophysicist at the University of Cambridge. 

He's called it a 'hycean' world – a relatively new term he coined for a rocky planet with a hydrogen-rich atmosphere and oceans of water.

'If we do detect DMS [on K2-18b] it does put it basically at the top for potential signs of habitability,' he told the Times. 

K2-18b – more than eight times the mass of Earth and over twice as big – was discovered in 2015.

But it was only in 2019 that the presence of water vapour in K2-18b's atmosphere was reported. 

Then, last year, the James Webb telescope detected carbon dioxide and methane in its atmosphere, as well as a shortage of ammonia.

Dr Madhusudhan called this a 'very profound moment' because it supports the theory that there's a water ocean underneath a hydrogen-rich atmosphere.

But it was the presence of something else that got astronomers even more excited. 

Planet K2-18b - more than eight times the mass of Earth and 120 light-years away - sits within the habitable zone of its star in the Leo constellation. It's closer to its star than the Earth is to the sun, meaning it has shorter years, completing its orbit in 33 days while ours takes 365

It is thought to be a 'Hycean' world (depicted) - a new class of exoplanet possessing key ingredients for alien species because of their hydrogen-rich atmospheres and oceans of water

More observations by the James Webb Space Telescope (pictured) could confirm the presence of DMS in the planet's atmosphere 

READ MORE Hopes of finding life on Jupiter's moon are DASHED 

Europa is comprised of an icy shell about 15 miles thick

Initial Webb observations provided a possible detection of a molecule called dimethyl sulfide (DMS), which on Earth is 'only produced by life'. 

The bulk of the DMS in Earth’s atmosphere is emitted from phytoplankton in marine environments – suggesting a similar form of life on the distant planet.

In fact, scientists have been unable to think of any natural geological or chemical process that could create DMS without living organisms. 

Dr Madhusudhan said the finding was a shock but because they were initial observations he could only say with 50 per cent confidence there is DMS on K2-18b. 

'It was a real shock, I had sleepless nights for a week,' he added.

'That week, I didn’t even muster the courage to break it to my own team.'  

Today, eight hours of observations by the James Webb telescope should provide a definitive answer – although the expert will have to spend months poring over the data to get it.

NASA's $10 billion (£7.4 billion) observatory is able to analyse the chemical make-up of a distant planet by capturing the light from its host star after it has passed through the planet's atmosphere on its way to Earth. 

Gases in the atmosphere absorb some of the starlight but each leave tell-tale signatures in the spectrum of light that astronomers can then unpick. 

James Webb telescope has detected key molecules, as depicted in this graph from a paper published last year. Today, the observatory will be specifically searching for dimethyl sulfide (DMS)

Although Hycean worlds are predicted to be covered in water, researchers say it is also possible that K2-18 b's hypothesised ocean is too hot to be habitable or be liquid. 

In fact, a study published earlier this year suggested the ocean may be lava. 

K2-18b is known as a 'super Earth' because it is bigger than our planet but smaller than Neptune. 

K2-18b's large size – with a radius 2.6 times the radius of Earth – means that the planet's interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. 

'Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,' said researcher Subhajit Sarkar of Cardiff University. 

'We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.'

The James Webb Telescope: NASA's $10 billion telescope is designed to detect light from the earliest stars and galaxies

The James Webb telescope has been described as a 'time machine' that could help unravel the secrets of our universe.

The telescope will be used to look back to the first galaxies born in the early universe more than 13.5 billion years ago, and observe the sources of stars, exoplanets, and even the moons and planets of our solar system.

The vast telescope, which has already cost more than $7 billion (£5 billion), is considered a successor to the orbiting Hubble Space Telescope

The James Webb Telescope and most of its instruments have an operating temperature of roughly 40 Kelvin – about minus 387 Fahrenheit (minus 233 Celsius).

It is the world's biggest and most powerful orbital space telescope, capable of peering back 100-200 million years after the Big Bang.

The orbiting infrared observatory is designed to be about 100 times more powerful than its predecessor, the Hubble Space Telescope.

NASA likes to think of James Webb as a successor to Hubble rather than a replacement, as the two will work in tandem for a while. 

The Hubble telescope was launched on April 24, 1990, via the space shuttle Discovery from Kennedy Space Centre in Florida.

It circles the Earth at a speed of about 17,000mph (27,300kph) in low Earth orbit at about 340 miles in altitude.