A stunning new photograph of Pluto, showing the dwarf planet silhouetted in front of the sun, has been released by Nasa.

Taken by the New Horizon spacecraft as it passed around 120,000 miles away, it was pieced together from six separate images that were taken on 14 July 2015, but not released until now.

It shows the unusual blue haze in Pluto’s atmosphere. Scientists are unsure what caused the phenomenon but believe the colour comes from sunlight hitting methane in the planet’s atmosphere.

This produces hydrocarbons that clump together, blocking sunlight and creating a blue shimmer. A similar process takes place in the Earth’s atmosphere.

The particles that produce the haze form numerous layers in the atmosphere, some of which extend for to up to 120 miles above the planet.

The outline of mountains on Pluto’s surface can also be seen near the top of the image. Each one pixel of the picture is the equivalent of one kilometre in distance.

Nasa has named the photo “Farewell to Pluto” because it was taken as the New Horizons module moved away from the dwarf planet.

In pictures: Nasa mission to Pluto Show all 5 1 /5 In pictures: Nasa mission to Pluto In pictures: Nasa mission to Pluto Mission to Pluto The 3 billion miles journey to Pluto began nine and a half years ago NASA In pictures: Nasa mission to Pluto Mission to Pluto A close-up image of a region near Pluto's equator reveals a range of youthful mountains rising as high as 11,000 feet (3,500 meters) above the surface of the icy body NASA In pictures: Nasa mission to Pluto Mission to Pluto Hydra, one of Pluto's moons, in an image obtained by the New Horizons spacecraft In pictures: Nasa mission to Pluto Mission to Pluto Charon, Pluto's largest moon, in a image taken from a distance of 289,000 miles (466,000 kilometers) NASA In pictures: Nasa mission to Pluto Mission to Pluto A NASA graphic of a spectra obtained by the Ralph instrument on the New Horizons spacecraft revealing methane ice on the frozen surface of Pluto NASA

The spacecraft launched in 2006 and spent nine years travelling to Pluto for a six-month observation.