NASA scientists said they discovered a fifth planet orbiting a star outside our own solar system and say the discovery suggests there are many solar systems that are, just like our own, packed with planets.

The new planet is much bigger than Earth, but is a similar distance away from its sun, a star known as 55 Cancri, the astronomers said on Tuesday.

Four planets had already been seen around the star, but the discovery marks the first time as many as five planets have been found orbiting a solar system outside our own with its eight planets, said Debra Fischer, an astronomer at San Francisco State University.

The world's largest passenger plane, the Airbus A380, has landed in Sydney on its first commercial flight, after a seven-hour journey from Singapore.

Singapore Airlines took delivery of the huge plane, dubbed the Superjumbo, just over a week ago. Passengers bought seats in a charity online auction.

It can carry some 850 passengers, but took about 450 to Sydney.

The superjumbo's advent ends a reign of nearly four decades by the Boeing 747 as the world's biggest airliner.