By Dr David Whitehouse BBC News Online science editor

In the outer reaches of the Solar System

It was discovered on Friday by an automated sky survey project designed to search for threatening asteroids that may be on an Earth impact course.

The object is about 570 km across, making it one of the largest bodies of its kind found in modern times.

The new body, made of rock and ice, is designated 2003 VS2. Re-examining past records, astronomers have found it in images taken as far back as 1998.

Resonance orbit

The object is one of the largest yet found in the Kuiper Belt, a region of space littered with small rocky worlds orbiting the Sun.

It was discovered by the automated Near Earth Asteroid Tracking (Neat) project using a large telescope at Mount Palomar in California, US.

KUIPER BELT OBJECTS Icy planetary bodies that orbit beyond Neptune in the distant region of the Solar System More than 400 such objects are currently known They are believed to be remnants of the formation of the Solar System and among the most primitive objects available for study

It is in a so-called resonance orbit with Neptune. This means that it completes two orbits of the Sun for every three completed by the eighth planet.

Such orbits are stable as they allow the object to approach Neptune's orbit without any possibility of collision. Pluto, currently the most distant true planet, is in such an orbit.

Because of the similarity astronomers have classified 2003 VS2 as the latest "Plutino", or "little Pluto". Dave Jewitt of the Institute for Astronomy of the University of Hawaii told BBC News Online that this Plutino was probably among the top ten Kuiper Belt objects found so far.

Since the first Kuiper Belt Object was discovered in 1992, several hundred have been found, and many of them are in the Neptune resonance condition, too.