Dec. 13, 2004 — The Cassini spacecraft zoomed past Saturn's largest moon early Monday, its radars and other science instruments piercing Titan's thick atmosphere in search of suspected liquid seas and atmospheric features.

Data began trickling in to NASA's Deep Space Network Monday evening — about 12 hours after the probe's closest approach to Titan. Cassini flew within about 750 miles, or 1,200 kilometers of the moon's surface. Details of the voyage will be released during a news conference on Thursday.

The flyby was Cassini's second Titan encounter. The probe arrived July 1 for a four-year mission. The first flyby produced more questions than answers about Titan, including indications that perhaps theories of liquid oceans were in error.

The second encounter, with the closest approach occurring at 6:38 a.m. ET, was devoted to refining information about Titan's atmosphere, which will help engineers determine how close they can plot future flybys.

The data also may be useful for European scientists fine-tuning plans for the Huygens spacecraft mission to Titan, slated for January. The probe is being carried aboard Cassini and will be released on Dec. 25 to begin its independent mission.

Scientists had planned to route Cassini on a path that would fly over Titan at a different angle than its first close encounter in October. But a trajectory shift caused by gravitational forces from the Saturn moon Iapetus forced Monday's flyby to be geometrically similar to Cassini's first pass.

Scientists plan to use the data to look for changes on Titan's surface and verify information obtained during the earlier encounter.

Investigations planned during Cassini's pass over Titan included a two-hour scan using infrared-sensitive detectors for previously undetected molecules in the stratosphere, which begins about 240 miles above the moon's surface. Cassini also was to collect temperature data to compile of thermal map of the stratosphere.

The flyby presented the Cassini imaging team with several opportunities for high-resolution photographs. The team is particularly interested in photographing the landing site for the Huygens probe, which is to make a parachute descent through the moon's atmosphere and touch down on Titan's surface.

As Cassini flies away from Titan, cameras were to be aimed to try to capture a view of the moon's north pole, illuminated by "Saturn-shine" — sunlight reflecting off Saturn.

Titan is the only satellite in the solar system with a sizeable atmosphere. Like Earth, Titan's atmosphere is comprised primarily of nitrogen. It also contains significant amounts of aerosols and organic hydrocarbons, such as methane and ethane.

The moon's face is masked by its thick, hazy atmosphere, but scientists believe the moon has the proper chemistry to produce lakes, seas or river. Other liquids also may exist beneath Titan's surface.

Results of Cassini's pass by Titan as it entered orbit six months ago, as well as its first dedicated flyby in October, show the moon to be more complex than originally thought.

Scientists are still searching for clear evidence of surface liquids. They also have yet to identify what processes are in play to account for observable surface features and atmospheric phenomena, such as clouds.

Monday's flyby was the second of 45 planned visits to Titan scheduled during Cassini's primary mission.