Saturn's largest moon, Titan, appears to be covered by oily oceans.

Astronomers used the world's largest radio/radar telescope in Puerto Rico to aim radar waves towards the smog-shrouded moon.

The observations suggest the presence of liquid hydrocarbon lakes on the surface in the form of methane.

Saturn's moon TitanCourtesy: NASA

It's the first time astronomers have major evidence of oceans on a planetary body other than on Europa, one of Jupiter's moons.

A Cornell University-led team analysed the dim signal. They say it points to the presence of craters filled with oily oceans or lakes below.

Titan is about 50 per cent larger than Earth's moon. It is the only satellite in our solar system with a dense atmosphere.

"The surface of Titan is one of the last unstudied parcels of real estate in the solar system, and we really know very little about it," said Cornell astronomer Donald Campbell in a release.

Campbell led the observation team.

Next summer, NASA's Cassini spacecraft is scheduled to go into orbit around Saturn and its moons for four years.

The European Space Agency's probe Huygens is piggybacking on Cassini. It will eventually plunge into Titan's hazy atmosphere and land on the moon's surface to take a look.

The study appears in Friday's issue of the journal, Science.