A New World is Uncovered

10/08/2011 15:27 | Updated 10 October 2011

This week, one hundred and fourteen million miles away, in deep space, where the sun is a fainter source of light than it is at Earth, in the vast but not empty gap between the planets Mars and Jupiter, a new world is being uncovered.

Today the Dawn spacecraft starts its first science orbit around the 350-mile wide rocky world called Vesta, and begins unravelling some of the secrets it has been keeping since the solar system was young.

Vesta was discovered in 1807 by the German astronomer Heinrich Wilhelm Matthäus Olbers. It was the fourth small world found between Mars and Jupiter in just a few years, and for almost 40 years they were considered true planets. It was only around 1845 that many more were discovered, and then classified as minor planets or asteroids.

There are countless such objects out there. Oblong worlds tumbling through space, mostly small but with a few really big ones like Vesta. They are the remnants of a planet that could not form due to the gravitational disruption caused by nearby Jupiter. Nothing large could accumulate there, and anything that tried was smashed asunder by other chunks of rock. But in the solar system's badlands there are clues about how our Earth formed.

When Vesta was young its interior became hot due to radioactive Aluminium. Its core became molten and metalic, like the Earth. Viscous rocks began circulating inside it before, as the radioactivity waned and its heart cooled, they began to crystalise and their motions became frozen forever. Molten rock poured out of cracks and coated parts of Vesta's surface meaning that there is in this tiny world, a microcosm of our own planet's history waiting to be deciphered.

Dawn will circle Vesta for a year before its ion-drive rocket glows once more to take it to another, larger, asteroid called Ceres. Unlike Vesta it is spherical and coated in ice. Astronomers class it as a true dwarf planet, and can't wait to see it up close.

These are extraordinary times for the exploration of the solar system. A few days ago the Mars rover Opportunity reached the rim of a large crater in whose rocks we will be able to determine more about the Red Planet's history and its long transition from a warm, waterworld of billions of years ago, to the frozen globe it is today. We have new probes arriving at the Moon, and one called Messenger having recently become the first ever to orbit the closest planet to our Sun - Mercury. Juno has just been dispatched to Jupiter and New Horizons is just a few years away from giving us our first ever close up of distant, enigmatic Pluto.

If you go out at midnight tonight and look due south, low down, you will be gazing deep in the constellation of Capricornus. Vesta and its visitor lies in the same direction, floating like a mote of dust in a sunbeam.