The second most massive resident of the asteroid belt, almost 200 million kilometres from the Earth between Mars and Jupiter, is the Vesta asteroid.

On Monday - thanks to NASA's Dawn spacecraft - the world got its first glance of the giant spinning ball that Mission Director Marc Rayman compared to a large U.S. state.

"At three hundred and thirty miles in diameter it has twice the surface area of California - this is a big place."

Dawn - the largest interplanetary probe ever launched by NASA - arrived at Vesta last month after a four year journey. 

"We believe this goes back to the first five million years of the solar system", said Chris Russell, Dawn Principle Investigator. Analysing the surface, "enables us to determine what has happened to Vesta over the eons."

Fresh colour photos show differences in the chemical composition of the asteroid's surface but what scientists really want to know is what caused the dark grooves that can clearly be seen on the asteroid's surface?

They also want to know what's going on in and around three huge craters that they have already nicknamed, "The Snowmen", according to Holger Sierks of the Dawn camera team. "They appear to be shallow and filled with debris."

NASA - stung by harsh criticism over the ending of the Space Shuttle programme - published the Vesta snaps less than two weeks after Shuttle Atlantis rolled to a halt at the Kennedy Space Center in Florida.

The four hundred million dollar Vesta project was conceived long before the United States decided to send astronauts to an asteroid by next decade but presumably the data gathered will help that mission.

Dawn will circle Vesta for the next year before moving off to film its icy neighbour Ceres, which it will reach in 2015.