Nasa’s New Horizons spacecraft has returned its first colour images of Pluto and its moon Charon.

It is now just three weeks until the spacecraft makes its historic flyby of the dwarf planet, a moment that has been decades in the making.

And in these latest images, it can be seen that Pluto and Charon have different colours - although exactly why is not yet known.

Scientists in Colorado have revealed new images of Pluto and Charon (shown). They are the first colour images of the two by the New Horizons probe. Pluto appears beige-orange and Charon is grey in the images. New Horizons will arrive at the Plutonian system on 14 July

The images, revealed by scientists in Colorado, were taken by New Horizons from a distance of about 30 million miles (50 million kilometres) over the course of a few days.

The images are close to what Pluto and its moon Charon would look like in true colour, although they show only a few pixels, because the spacecraft is still so far away.

They were taken using the Multicolour Visible Imaging Camera on the instrument known as Ralph.

‘It’s exciting to see Pluto and Charon in motion and in colour,’ said New Horizons Principal Investigator Dr Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado.

‘Even at this low resolution, we can see that Pluto and Charon have different colours - Pluto is beige-orange, while Charon is grey.

‘Exactly why they are so different is the subject of debate.’

This animation, made by stitching nine images together, shows the rotation of Charon around Pluto in colour, with Pluto at the centre. Charon completes an orbit every 6.4 days, exactly the same amount of time it takes Pluto to rotate, so the moon remains at the same point above the surface

On 14 July, after a journey of three billion miles and more than nine years, and more than two decades of planning, New Horizons (artist's impression shown) will fly past Pluto. The flyby, lasting just a few hours, will see it pass 7,800 miles (12,500km) above the surface, the first ever mission to Pluto

The images, revealed by scientists in Colorado, were taken by New Horizons from a distance of about 30 million miles (50 million kilometres) over the course of a few days.The images are close to what Pluto and its moon Charon would look like in true colour, as seen in this view from one of Pluto's other moons

PLUTO AND CHARON Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth. It is about two thirds the size of our moon. With a surface temperature estimated to be -229°C (-380°F), the environment at Pluto is too cold to allow liquid water on its surface. Pluto's moons are also in the same frigid environment. The moon Charon is almost half the size of Pluto, and it is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system. The distance between them is 12,200 miles (19,640 km). Charon's orbit around Pluto takes 6.4 Earth days. The two are gravitational locked, so Charon neither rises nor sets, but hovers over the same spot on Pluto's surface. Advertisement

On 14 July, after a nine-year journey of three billion miles, and more than two decades of planning, New Horizons will fly past Pluto.

The flyby, lasting just a few hours, will see it pass 7,800 miles (12,500km) above the surface, the first ever mission to Pluto.

Using its array of instruments and cameras, New Horizons will help answer questions about Pluto’s surface, its atmosphere and its moons.

After the fly past, one or several Kuiper Belt Objects (KBOs) will be picked for further study.

A second animation of images was also created, this time showing the orbit of Pluto and Charon based on their common centre of gravity, denoted by an ‘x’.

Pluto completes a rotation every six days, nine hour and 17.6 minutes, and in the animations a shift in the dwarf planet’s brightness can be seen.

This is likely due to lighter and darker regions on the different faces on Pluto.

A second animation of images was also created, this time showing the orbit of Pluto and Charon based on their common centre of gravity, denoted by an ‘x’, seen here

Charon is the largest of Pluto's five moons, and is so large that it and Pluto are sometimes said to be a binary planet system. Shown is the Plutonian system as imaged by the Hubble Space Telescope

The images will gradually get better and better over the next few weeks, culminating in the best images on 14 July.

‘Colour observations are going to get much, much better, eventually resolving the surfaces of Charon and Pluto at scales of just kilometers,’ said Dr Cathy Olkin, New Horizons deputy project scientist from SwRI.