Nasa probe enters Ceres orbit to take closer look at dwarf planet

The Dawn spacecraft has started orbiting Ceres, the largest-known body in the asteroid belt between Mars and Jupiter, taking “close-up” images that scientists hope will reveal the mystery of a pair of bright spots on the dwarf planet.

Scientists have been intrigued by earlier images from the Nasa probe of 1,000 kilometre-wide Ceres, with the brighter of the two spots in a crater reflecting at least 40 per cent of the sunlight that falls on it.

Given that frozen water makes up at least a quarter of the bulk of Ceres, speculation so far is that they may well be patches of primordial ice. The bright spots might also be the work of volcanic eruptions on Ceres that blast ice out from the body’s interior.

Yet another explanation could be the materials that make up the object. Some asteroids shine brightly because of their mineral properties. Known as enstatite asteroids, they are rich in magnesium silicates, which can reflect nearly half of the light they receive.

Dawn, which was launched in 2007, will spend the next 16 months photographing its icy surface.

First classified as a planet, Ceres was later demoted to an asteroid. In 2006 it was re-classified as a dwarf planet. Dwarf planets are spherical celestial bodies revolving around the sun, similar to a planet but not large enough to gravitationally clear its orbital region of most or all other celestial bodies.