The Ceres asteroid orbits the sun between Mars and Jupiter

               Speck is in fact Ceres – a strange world that could reveal the origin of life on Earth.The image was taken when the Dawn spacecraft was around 740,000 miles (1.2 million km) from Ceres, on its way to meet the asteroid.Dawn will be captured into Ceres' orbit in March, marking the first visit to a dwarf planet by a spacecraft.

               Ceres, the largest asteroid in the solar system, orbits the sun in the asteroid belt between Mars and Jupiter.

'Now, finally, we have a spacecraft on the verge of unveiling this mysterious, alien world,' Dawn mission director and chief engineer Marc Rayman, of Nasa's Jet Propulsion Laboratory in Pasadena, California said.

                Soon it will reveal myriad secrets Ceres has held since the dawn of the solar system.'The image was taken as part of a final calibration of the science camera before Dawn's arrival. On December 1, Ceres was about nine pixels in diameter - nearly perfect for this calibration.It provides data on very subtle optical properties of the camera that scientists will use when they analyse and interpret the details of some of the pictures returned from orbit.Ceres is the bright spot in the centre of the image.

                 Because the dwarf planet is much brighter than the stars in the background, the camera used a long exposure time to make the stars visible.The long exposure made Ceres appear overexposed, and exaggerated its size; which was corrected by superimposing a shorter exposure of the dwarf planet in the centre of the image.Ceres is 590 miles (950 km) across and was discovered in 1801.

                  In January, researchers discovered that water was gushing from its surface at a rate of 13lb (6kg) per second.Observations by the European Space Agency's Herschel telescope suggested they could be coming from geysers or ice volcanoes.Ceres orbits the sun in the asteroid belt between Mars and Jupiter and is very similar to Jupiter's moon Europa and Saturn's moon Enceladus - both considered potential sources for harbouring life.

                   Dr Michael Kuppers, of the Esa's lab in Villanueva de la Canada in Spain said: 'Although ground and space-based observations may further map the behaviour of Ceres over its orbit the Dawn spacecraft mission arriving to orbit Ceres in early 2015 is expected to be key in providing a long-term follow-up on the water outgassing behaviour of Ceres.

               'The presence and abundance of water in bodies like Ceres could have relevance for the origin of life on Earth and the large-scale migration of planets such as Jupiter.

                   One scenario suggests as the giant planets migrated they disturbed populations of small rocky and icy asteroids and comets which hit the early Earth and Moon - delivering organic molecules and water to Earth.