The Cassini spacecraft on Tuesday cruised to within 745 miles of Titan, Saturn’s planet-size moon, for the first close encounter with it. The moon, long an enigma wrapped in smog, has been described by one scientist as the ‘‘largest unexplored surface in the solar system.’’Scientists and flight controllers here at NASA’s Jet Propulsion Laboratory had to wait hours to learn if the mission was a success. While Cassini’s cameras, radar system and other instruments were surveying the moon, as planned, its antenna was facing Titan and unable to communicate with Earth.Late Tuesday evening, radio transmission from the spacecraft confirmed that the flyby was successful and pictures of Titan were being received. Mission officials had said they had reason to be optimistic.Dr Earl H. Maize, the deputy program manager, noted that the spacecraft and all systems were ‘‘in perfect shape’’ before the encounter. A rocket maneuver over the weekend had put Cassini on course to give scientists a revealing look at the moon’s surface while passing safely above the outer fringe of its dense atmosphere.The moment of closest approach to Titan presumably occurred at 12:44 pm ET. The first detailed exploration of Titan is perhaps the most eagerly anticipated goal of the $3.2 bn Cassini mission. Spacecraft began orbiting on June 30.Titan, larger than the planets Mercury and Pluto and second in size only to Jupiter’s giant satellite Ganymede, is a bitterly cold world — minus 290 degrees Fahrenheit — but with an active carbon-based chemistry that creates the thick smog and may shed light on conditions that contributed to the origin of life on Earth.Dr. Tobias Owen, a planetary scientist at the University of Hawaii at Manoa, called Titan, with a diameter of 3,200 miles, the largest unexplored surface in the solar system. And a strange landscape it may be: ridges and deep cracks, stretches of ice and tar, pools of liquid hydrocarbons, perhaps resembling, in Owen’s description, “a frozen chocolate sundae.’’‘‘We’re not expecting to find life — it’s too cold — but are expecting to find prebiotic chemistry like that in the very earliest days of Earth,’’ Owen said.Titan is also intriguing because it is the only moon in the solar system with a substantial atmosphere and its main constituent is nitrogen, as is Earth’s. Owen said that Titan may prove to be a natural laboratory for studying the origin of Earth’s own atmosphere.Dr. Torrence V. Johnson of the Jet Propulsion Laboratory, a member of the imaging team, said scientists did not know what they would find. ‘‘I’m expecting to be pleasantly bewildered,’’ Johnson said, adding the findings would probably challenge preconceptions and provoke ‘‘lively debate among scientists.’’In previous photography by two Voyager spacecraft passing at much greater distances and the Hubble Space Telescope, Titan was heavily veiled in pale yellow light, like a fuzzy tennis ball. Cassini’s first pass at Titan, at a distance of 200,000 miles, yielded little more than dark smudges on the surface and puffy white methane clouds near the south pole.At this distance, Cassini’s wide-angle and narrow-angle cameras were designed to penetrate the opaque smog and lower clouds to photograph surface features down to the size of a football stadium. —NYT
