PASADENAt, July 1: Hours after it completed a journey of nearly seven years to Saturn, the spacecraft Cassini sent its first pictures back to Earth on Thursday, showing sharp edges and ripples of energy in the planet's enormous rings.

The early photos, taken from the unilluminated side of the rings, were full of electronic "noise" and only in black and white, but were still clear enough to show fine ring structures and edges sharper than might be expected, given all the particles in the rings colliding with each other.

"Ring scientists love sharp edges. They're very mysterious - they have to be held sharp by some mechanism," said Carolyn Porco, leader of the Cassini imaging science team.

Scientists were thrilled with the quantity and clarity of the images - the closest pictures of the rings that will be taken during the mission. "These images are more or less serendipity," Porco said.

The images also showed "density waves," disruptions in the particles in the rings caused by the energy of moonlets passing outside them, that scientists said could best be compared to the pattern of bunching and thinning out seen in traffic jams.

Scientists from NASA and other international agencies cheered and called the photos "beautiful" and "mind-blowing." "It's so flawless it almost seems faked - but it's not," Porco said in live commentary from the Jet Propulsion Laboratory here.

The truck-sized probe slipped through those rings and entered orbit around Saturn on Wednesday night, after travelling 2.2 billion miles (3.5 billion km) since its October 1997 launch. Along the way, it used the gravity of Venus, Earth and Jupiter to slingshot it out to the sixth planet from the sun.

Cassini is set to spend at least four years studying the planet, its rings and some of its 31 known moons. Much of that time will be dedicated to Titan, one of the solar system's largest and most intriguing moons, with an atmosphere and composition that have inspired science fiction dreams of an emerging home for life. -Reuters