US astronomers announced last month they may have found a ninth planet beyond Neptune, but conceded they had no idea where on an estimated 10,000-20,000-year orbit it might be.

On Tuesday, a French science quartet said they have narrowed the search area.

By studying data from NASA's Cassini spacecraft orbiting Saturn, the seventh planet from the Sun, they could exclude two zones, the team wrote in the journal Astronomy and Astrophysics.

Their work confirmed that a ninth planet might exist in the far reaches of our Solar System, co-author Jacques Laskar of the Paris Observatory told AFP, "but not just anywhere".

Based on mathematical modelling, the French scientists calculated what influence a ninth planet -- travelling along the orbit postulated by the Americans -- would have on the movement of other planets as it passed nearby.

They then looked at how the known planets actually behaved.

The postulated planet is thought to circle the Sun in a lopsided, highly elongated, oval loop.
At its most distant from the Sun, the planet would be too far too away for any effect on other planets to ever be detectable, thus limiting