The spacecraft Cassini, which successfully entered the Saturn's orbit late Wednesday, sent back the first images of the giant planet's rings to Earth early Thursday.

The first images taken from the unlit side of the rings when the probe entered orbit late Wednesday were followed by increasingly clear pictures on Thursday. Pictures arrived later at Earth were taken from the sunlit side of the rings. All the images show fine ring structures and surprisingly sharp edges.

Mission scientists at NASA's Jet Propulsion Laboratory called the photos "beautiful" and "mind-blowing." They still need time to analyze the images. Scientists believe data from the Saturn system can help them understand how the planets of the Solar system evolved.

Cassini entered Saturn's orbit late Wednesday as planned. After a safe flight through Saturn's ring plane with its high-gain antenna oriented forward to shield it from small particles, Cassini performed a critical engine firing to slow it down so it could be captured by the gravitational force of Saturn, the sixth planet from Sun and the second largest.

The orbit insertion came after two decades of work by about 260 scientists from the United States and 17 European countries. The 3.3-billion-US dollar mission, which was funded by NASA, the European Space Agency and the Italian Space Agency, has been hailed as a model of international cooperation.

Cassini is expected to make 76 orbits and repeated fly-bys at seven of the 31 known moons of Saturn in the next four years or more, for the study of Saturn, its rings and some of its moons.

In December, it is planned to release from its back the smaller probe Huygens, which is expected to fall on the surface of Saturn's largest moon Titan in January to conduct a brief study of Titan's atmosphere.

The Cassini and Huygens probes are named after 17th century astronomers Jean Dominique Cassini and Christiaan Huygens.

Major facts of Cassini space probe of Saturn

Cassini, named after 17th century Italian-French astronomer Jean Dominique Cassini, who discovered four Saturn moons, was sent to explore Saturn, its rings, magnetic fields and icy moons.

Power: Nuclear powered

Launch: Oct. 15, 1997, from Cape Canaveral, Florida

Saturn arrival: June 30, 2004 PT (July 1 GMT)

Flight distance to Saturn: 3.5 billion km

Primary mission: four years

Cost: 3.27 billion US dollars, including 2.6 billion dollars from the United States and 660 million dollars from Europe

Size: 6.6 meters long and 3.9 meters wide

Weight: 5,712 kg.

Instruments: 18 in total, including cameras, ultraviolet imaging spectrograph, radar, plasma spectrometer, infrared spectrometer, ion and neutral mass spectrometer, magnetometer, cosmic dust analyzer

Development partners: the US NASA, the European Space Agency, the Italian space agency Agenzia Spaziale Italiana

Personnel and countries involved: abut 260 scientists from 18 countries

HUYGENS PROBE:

The Huygens probe will explore Titan, Saturn's largest moon believed to have a "pre-biotic" environment. The craft, developed by the European Space Agency, is named after 17th century Dutch astronomer Christiaan Huygens.

Size: about 2.7 meters in diameter and 317 kg in weight

Release from Cassini: Dec. 24, 2004

Titan landing: Jan. 14, 2005

Instruments: imaging equipment, Doppler wind experiment, gas

chromatograph and mass spectrometer, atmospheric structure

instrument, surface science package

SATURN FACTS:

6th planet from the sun

Distance from sun: 1.43 billion km or about 10 times as far as

Earth and twice as far as Jupiter

Number of moons: 31 known

Number of rings: seven

Saturn year (time to orbit around the sun): 29.42 Earth years

Saturn day (time to rotate): about 10.5 hours