While the possibility of a catastrophic asteroid slamming into Earth is extremely rare, it may only be a matter of time before this threat becomes a reality.

But experts have warned that humans are not prepared for an asteroid impact, and should one head for Earth, there's not much we can do about it.

A Nasa scientist has said that our best hope is building an interceptor rocket to keep in storage that could be used in deflection missions.

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Experts have warned that humans are not prepared for an asteroid impact, and should one head for Earth, there's not much we can do about it (stock image)

Dr Joseph Nuth, a researcher at Nasa's Goddard Space Flight Centre in Maryland was speaking at the annual meeting of the American Geophysical Union earlier this week.

He said: 'The biggest problem, basically, is there's not a hell of a lot we can do about it at the moment.'

While dangerous asteroids and comets rarely hit Earth, Dr Nuth warned that the threat was always there.

He said: 'They are the extinction-level events, things like dinosaur killers, they're 50 to 60 million years apart, essentially.

'You could say, of course, we're due, but it's a random course at that point.'

In the past, comets have come very close to hitting Earth.

In 1996, a comet narrowly missed our planet, instead flying into Jupiter, and again in 2014, a comet passed 'within cosmic spitting distance of Mars', according to Dr Nuth.

And comets are often only discovered when it's too late to launch a deflection mission.

Dr Nuth said: 'If you look at the schedule for high-reliability spacecraft and launching them, it takes five years to launch a spacecraft.

Nasa is planning an ambitious mission that will see a robotic spaceship visit an asteroid to create an orbiting base for astronauts. Nasa plans to study the asteroid and test deflection techniques that one day may be necessary to save Earth from a catastrophic collision

'We had 22 months of total warning.'

Dr Nuth advises that Nasa should build an interceptor rocket alongside an observer spacecraft, which he says could cut the five-year delay to launch in half.

And if a rocket could be devised that could launch within a year, Dr Nuth says it 'could mitigate the possibility of a sneaky asteroid coming in from a place that's hard to observe, like from the sun.'

This is not the first time that experts have warned that the Earth is unprepared for an asteroid strike.

In September, director of the Office of Science and Technology Policy, John Holdren, warned that an impact could 'do a lot of damage to the Earth.'

The expert noted two catastrophic events in recent history that took the world by surprise – the Chelyabinsk strike in 2013, and the Tunguska fireball in 1908.

While scientists have made great strides in detecting potentially hazardous Near-Earth Objects, Mr Holdren explained that there is still much work to be done.

In the 1998 film, Armageddon, humans discover that an asteroid that size of Texas is on course for the Earth. And experts believe that this could one day be the case, if a deflection mission is not sent

'We are not fully prepared, but we are on a trajectory to get much more so,' Mr Holdren said.

Events like the Chelyabinsk strike and the Tunguska explosion are extremely rare, he said, with the first thought to occur once every hundred years and the latter every 1,000.

But, 'if we are going to be as capable a civilization as our technology allows, we need to be prepared for even those rare events, because they could to a lot of damage to the Earth.'

Despite how unusual these events may be, these strikes could have devastating effects on the planet, and Earth must be prepared.

The expert warned: 'Ultimately, we may need to deflect an asteroid on a collision course with the Earth.

'This is a hazard that 65 million years ago the dinosaurs succumbed to. We have to be smarter than the dinosaurs.'

Mr Holdren says that Nasa's Asteroid Redirect Mission could provide the necessary education on how to handle these threats.

The so-called Asteroid Redirect Mission is estimated to cost about £1.1 billion ($1.4 billion) not including launch costs and is targeted for liftoff in December 2021.

In the planned mission, a robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming a destination to prepare for future human missions to Mars, the US space agency has revealed.

Following a key program review, Nasa has approved the Asteroid Redirect Mission (ARM) to proceed to the next phase of design and development for the mission's robotic segment.

ARM is a two-part mission that will integrate robotic and crewed spacecraft operations in the proving ground of deep space to demonstrate key capabilities needed for Nasa's journey to Mars.

In the Spacecraft Structures Lab at Nasa's Langley Research Center, the Asteroid Redirect Mission robotic contact and restraint system is prototyped and tested

The crewed segment, targeted for launch in 2026, remains in an early mission concept phase, or pre-formulation.

'This is an exciting milestone for the Asteroid Redirect Mission,' said Nasa Associate Administrator Robert Lightfoot.

'Not only is ARM leveraging agency-wide capabilities, it will test a number of new technologies already in development.'

The robotic component of the ARM will demonstrate the world's most advanced and most efficient solar electric propulsion system as it travels to a near-Earth asteroid (NEA).

NEAs are asteroids that are fewer than 121 million miles (1.3 AU) from the sun at the closest point in their orbit.

Although the target asteroid is not expected to be officially selected until 2020, Nasa is using 2008 EV5 as the reference asteroid while the search continues for potential alternates.

In the planned mission, a robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming a destination to prepare for future human missions to Mars, the US space agency has revealed

Before beginning its trip to lunar orbit, the ARM spacecraft will demonstrate a widely supported asteroid deflection technique called a gravity tractor.

The spacecraft plus the mass of the captured boulder will create a small gravitational attraction to alter the orbit of the large asteroid.

After collecting a boulder from the asteroid, the robotic spacecraft will slowly redirect the boulder to an orbit around the moon, using the moon's gravity for an assist, where Nasa plans to conduct a series of proving ground missions in the 2020s.

There, astronauts will be able to select, extract, collect, and return samples from the multi-ton asteroid mass, and conduct other human-robotic and spacecraft operations in the proving ground that will validate concepts for Nasa's journey to Mars.