Astronomers have discovered two more tiny moons orbiting the distant planet Uranus. It means that Uranus overtakes Saturn as the planet with the largest number of moons.

One of the new moons

The new worlds were discovered by a team of astronomers led by Dr J.J. Kavelaars of McMaster University in Canada. The new satellites' orbits are highly elliptical and inclined to the planet's equator.

The two new satellites bring the total around Uranus to 20. They have been given the provisional names of 1999 U1 and 1999 U2. Eventually they will be named after Shakespearean characters.

They have diameters less than 20 kilometres and are made of dark rock. The discovery was announced in an International Astronomical Union circular.

Two years ago, Dr Kavelaars and three other scientists found two other satellites around Uranus, the 16th and 17th which are now named Caliban and Sycorax.

Three months ago, Dr Erich Karkoschka of the University of Arizona found an 18th satellite on a 1986 Voyager 2 photograph.