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Far beyond the orbit of Neptune, trillions of comets left over from the formation of the solar system lie in wait in a region known as the Oort cloud.

Here they are kept in relatively stable orbits around the sun, posing little threat to Earth save for the occasional icy rock that ventures inwards.

But in the blink of a cosmic eye that could all change, when a star passes near our solar system in 240,000 years - and it will possibly shower the planets with thousands of deadly comets.

A scientist from the Max Planck Institute in Germany says a star could have a closer encounter with Earth 'soon' - in cosmic terms. Dr Coryn Bailer-Jones says there is a 90% chance one will come close in 240,000 to 470,000 years. This will disturb the orbits of distant comets - sending them towards Earth (illustrated)

According to Dr Coryn Bailer-Jones from the Max Planck Institute for Astronomy in Heidelberg, Germany, there are several stars that could pose a danger to our solar system.

As our sun performs its cosmic dance around the Milky Way, it comes closer to and further from other stars in the vicinity.

He said that in as few as 240,000 years, there is a 90 per cent chance that one of these stars will come as close as 0.13 light-years to the solar system.

This may sound distant, but considering the Oort cloud extends to about 0.8 light-years, it is clearly too close for comfort.

Dr Bailer-Jones says an approaching star could disturb this region and be a threat to Earth.

'Stars which pass close to the sun can perturb the Oort cloud, injecting comets into the inner solar system where they may collide with the Earth,' he wrote in his paper.

He used data from Esa's Hipparcos spacecraft, which scanned the sky in the 1990s, to study the future of 50,000 stars.

The star of most danger is Hip 85605, a star slightly smaller than our sun that will come between 0.13 and 0.65 light-years in 240,000 to 470,000 years.

The possibility that an incoming star could disturb the Oort cloud in such a way to threaten the planets has been known for a while.

But this is one of the most accurate estimates yet for when and where a star will actually approach the solar system.

It should be noted that the position and motion of Hip 85605 may be incorrect, meaning it will not pass so close.

But even so, there are other stars that will take its place. A dwarf called GL 710, for example, has a 90 per cent chance of coming within 0.3 to 1.4 light-years in 1.3 million years.

The Oort cloud (illustrated) is a vast and mysterious region that is thought to surround our solar system. It contains trillions of comets left over from the birth of the universe - and possibly larger objects like dwarf planets as well. Long-period comets originate here, while short-period comets come from the Kuiper Belt

Speaking to MailOnline, Dr Bailer-Jones said that while the star could come close in cosmic terms, it might not be obviously noticeable to our distant descendants.

In addition, he says the process through which comets are sent into the solar system will take millions of years, and will likely increase the current rate of 10 or so comets a year to a hundred.

'If there are people around at that time in the future and they look up in the night sky, they wouldn't particularly notice the star,' he explained.

'Calculation of one object suggests it would be slightly brighter than Venus, which is pretty bright, but not as bright as the moon or sun or anything.'

But he says such an encounter is 'inevitable,' although the chances of a star actually entering the solar system is close to zero.

Using Hipparcos data, Dr Bailer-Jones has been able to look forward and back in to the future about 20 million years.

With data from the Gaia spacecraft, however, he hopes to extend this to about 50 million years - which will likely reveal more stars that once encountered our solar system, or will do in the future. 

Dr Bailer-Jones used data from Esa's Hipparcos spacecraft, shown left, which scanned the sky in the 1990s, to study the future of 50,000 stars. He plans to use data from the Gaia spacecraft (illustrated right) in 2016 to create even more accurate models of future and past stellar encounters with Earth

It's believed that a stellar encounter in the past may have caused comets to come towards Earth, possibly even causing the rock that killed the dinosaurs (illustration shown) to hit our planet. Dr Bailer-Jones hopes to use data to look 'back in time' and see if this is true

It is not just a disturbance in the Oort cloud that would threaten life on Earth, but also radiation from the stars themselves.

'If intense enough - and in particular if the star turned supernova during an encounter - then such ionising radiation could kill organisms outright, erode the Earth's ozone layer to expose life to harmful solar UV radiation, or induce long-term global calling through the nitrogen dioxide produced in our atmosphere,' wrote Dr Bailer-Jones.

He notes that there are several events throughout history that have been linked to cosmic events.

The mass extinction of the dinosaurs 65 million years ago, for example, was almost certainly formed by some form of large impact.

A layer of iron-60 radioisotopes deposited at the bottom of the ocean 2.8 million years ago, meanwhile, is suspected to be the result of a nearby supernova.

And other nearby supernova have been blamed for more mass extinctions on Earth.

Dr Bailer-Jones says to truly know how much danger we will be in, though, more data is needed.

This will hopefully be returned by Esa's Gaia spacecraft in 2016, which is currently mapping one billion stars in the Milky Way - one per cent of its total stars.

And he also wants to use the data to look backwards in time, and see if any craters on Earth could be explained by close passes of stars.