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For the first time, water ice has been spotted in images of craters on the planet Mercury by Nasa's Messenger spacecraft.

The groundbreaking discovery reveals the shape and size of the ice in the planet's polar regions.

It might also help us discover how water was transported to other planets in the solar system such as Mars and Earth.

Scientists at the Johns Hopkins University Applied Physics Laboratory have spotted ice in visible image of Mercury for the first time. One area was Kandinsky crater, near Mercury's north pole. On the right is a higher contrast image of the crater, revealing an expanse of ice on its floor

Water ice was speculated to exist on Mercury by Messenger back in 2012. However, this is the first time ice has been seen in visible images of the surface.

Found in permanently shadowed craters, it is thought to be tens of metres thick but may extend over vast regions of the crater floors. 

In addition the ice may be relatively young, on the order of just ten or 100 million years.

Why the ice can only exist in these craters, and not elsewhere on the surface, is due to Mercury's position in the solar system. 

Mercury is the closest planet to the sun, at an average distance of just 36 million miles (58 million kilometres).

It completes a rotation about once every 58 Earth days, meaning that its entire surface is subjected to the full brunt of the sun.

Without an atmosphere to protect the surface the temperatures reach a scorching 427°C (800°F) in the day this drops to -173°C (-280°F) at night.

These huge fluctuations make it impossible for ice or water to form on most of the surface.

However, in the polar regions of Mercury, some of the crater floors stay in endless shadow.

As the planet rotates it tilts in such a way that sunlight can never enter some of the craters at these extreme regions, so they stay eternally dark.

This means that ice can survive, as it is never heated to a high temperature by the sun and instead stays far below zero.

Back in 2012, Nasa spotted water ice in its permanently shadowed craters through a number of indirect methods.

But with these new images the ice has now been directly imaged, something Dr Nancy Chabot, the Instrument Scientist for Messenger, tells MailOnline is 'very exciting'.

This close-up of the Kandinsky crater image shows the ice in more detail. Dr Chabot tells MailOnline it is likely tens of metres thick but may extend across almost the entirety of the crater floor. How the ice came to be there though is somewhat of a mystery. It may have been carried by a comet

This image reveals the permanently shadowed surface within Prokofiev crater, the largest crater in Mercury's north polar region. The area in yellow, a zoomed in segment of the pink rectangle, is thought to be water ice residing inside the crater

'The main implications, aside from it being cool to see ice on Mercury, is that these cold traps are cold enough to have had ice for billions of years,' says Dr Chabot.

However it's thought that some of the ice was deposited fairly recently in cosmic terms, perhaps just ten or 100 million years ago.

'Even though you have water ice, we don't think there's the other things you need to have life,' she explains.

'We might not have life there, but understanding the delivery of water from the early solar system to Earth, Mars and other places that might have life. Understanding how water was distributed has implications for the solar system.'

To find the ice the researchers zeroed in on craters that had previously been identified to have bright material that could be ice.

This included Prokofiev, the largest crater in Mercury's north polar region.

By increasing the contrast in images, the ice in the crater floor was revealed.

Dr Chabot adds that the discovery may indicate ice formation on Mercury is something that is still continuing today.

But, most importantly, ice was likely taken to the planet by comets.

It is thought that other planets in the solar system, including Earth, had water and possibly life delivered in this way.

Discovering how this ice came to be on Mercury could, in turn, reveal the origins of our own water and ice on Earth, and even ourselves.

Messenger (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a Nasa-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. It entered orbit around Mercury on 17 March 2011