US-European spacecraft Cassini became the first man-made object that orbits Saturn late Wednesday for a four-year study of Saturn and its rings that can reportedly help understand how planets of the solar system evolved.

When Cassini started orbiting Saturn as planned around 12 p.m. EDT (0400 GMT Thursday), the mission control at the US Jet Propulsion Laboratory erupted in cheers for the success.

The critical step of orbit insertion began at 10:36 p.m. EDT Wednesday (0236 GMT Thursday), with Cassini's main engine to burn for the spacecraft to slow to be captured by the gravitational force of Saturn, the sixth planet from the sun.

The engine continued its burning which ended at 12:12 p.m. EDT (0412 GMT Thursday) after Cassini entered the orbit.

Before the engine burn, Cassini's high-gain antenna was oriented forward to shield the spacecraft from impact during a 90-minute and 158,000-km flight through Saturn's ring plane.

Cassini could have flown past Saturn if the engine burn failed to properly slow it down.

Nuclear-powered Cassini is planned to complete 76 orbits in the next four years or more and make 52 close passes at seven of Saturn's 31 known moons. It will fly closest to Saturn during the first orbit, to be within 80,230 km from the planet's center and about 19,980 km from its cloud tops.

The first images taken by Cassini are expected to reach Earth at about 8 a.m. EDT (1200 GMT) on Thursday.

Cassini is 6.6 meters long and 3.9 meters wide and weighs 5,670kg. It carries 12 scientific instruments and probe Huygens which is developed by the European Space Agency. Huygens, about 2.7 meters in diameter and 317 kg in weight, will be released from Cassini on Dec. 25 and penetrate on Jan. 14 the atmosphere of Titan, Saturn's largest moon.

Titan is believed to have a "pre-biotic" environment. Its investigation can reportedly help understand how the primitive Earth evolved into a life-bearing planet.

Cassini was launched from Cape Canaveral, Florida, on Oct. 15, 1997, and has completed a 3.5-billion-km interplanetary journey. The 3.3-billion-US-dollar Cassini-Huygens project was first proposed in 1982 and is joined by NASA, the European Space Agency and the Italian Space Agency. About 260 scientists from 18 countries have been taking part in it.