Titan is half again as large as Earth's Moon. It is the only satellite in the solar system with a serious atmosphere. Like Earth's air, Titan's is mostly nitrogen. Problem is, Titan's atmosphere is so thick with natural smog that astronomers can hardly see through it, so they know little about what exists at the surface.

For decades, researchers have speculated that Titan could harbor liquid lakes or seas made of hydrocarbons, which would rain out of the atmosphere as a result of sunlight breaking down methane, also prevalent in the air.

Titan has a preplanned entry course, but the specific landing site cannot be chosen, said Lebreton. Wind could carry the probe to sites as potentially distant as the Bahamas are from Miami.

Since the Huygens capsule is designed to take pictures and sense its environment on the way in, beaming the data back to Cassini, researchers should learn exactly what happens after Cassini relays the data to Earth.

"Images by the camera a few kilometers above the surface and a few minutes before landing should show if we are coming down on land or sea," Lebreton explained.

The 700-pound (318-kilogram) probe will report on Titan's surface for as brief as three minutes or as long as a half-hour, according to NASA, which manages the Cassini mission.

Several instruments -- an impact sensor, accelerometer and tilt sensor -- should confirm what sort of surface the probe lands on or in, Lebreton said. "After impact, an acoustic sonar will measure the depth of the sea down to about 1 kilometer [0.62 miles]" if it indeed lands in liquid.

A sea landing has one clear advantage: The probe will bob into an upright position -- important for getting data up to Cassini.

Built by the European Space Agency, the detachable probe aboard Cassini is named for Christiaan Huygens (1629-1695), a Dutch astronomer who discovered Titan and also figured out that Saturn had rings (Galileo had earlier spied the rings, which looked like lobes on the planet, and he could not explain what he saw).

Cassini will arrive at Saturn early next year, study the planet and its rings and also gather more data on Titan's atmosphere. It will release Huygens several months later.

Scientists have high hopes for the combined assault on the smoggy satellite.

Some scientists see Titan as resembling the early Earth, where organic molecules formed prior to life developing. Few expect the moon to harbor life, at least not life as we know it. The surface is frigid, with temperatures hovering around minus 288 degrees Fahrenheit (-178 degrees Celsius). While hydrocarbons can be liquid at that temperature, the water expected to exist on Titan would all be frozen solid. And liquid water, biologists say, is crucial for all known life forms.

Scientists are intrigued, though, by how Titan seems to regenerate methane.

If the hydrocarbons form when sunlight breaks down methane in the atmosphere, why is there still methane in the air? On Earth, life refreshes the methane supply. Theorists have suggested that methane seas on Titan would serve to replenish the atmospheric supply.

A splashdown on Titan is by no means certain.

"The surface of Titan is one of the last unstudied parcels of real estate in the solar system," said Donald Campbell, a Cornell University astronomer who led the new radar study, "and we really know very little about it."

Campbell's team can't rule out that the mirror-like glints came from very smooth, solid surfaces. But, he said in a telephone interview, the signature of the glints looks more like reflective liquid.

The radar reflections were evident in about three-fourths of the 25 observations, each aimed at a different part of Titan's equatorial region. If those observations are representative of the whole moon, Campbell said, then it's possible the satellite is up to 75 percent liquid, though the seas would not be global in nature, but rather split up into patches.

Ralph Lorenz of the University of Arizona analyzed Campbell's work for Nature. He said the transient nature of the glints suggest liquid regions that are 30 to 93 miles (50 to 150 kilometers) across.

"These features may be impact craters," Lorenz writes, "that have filled to form lakes and seas. The radar data suggest that as much as 75 percent of Titans surface could be covered in this way." Scientists have long theorized that Titan could be mottled by craters, much like Earth's Moon. And other studies have indeed indicated Titan's topography is not simple.

Only Huygens -- which will reach Titan on Jan. 14, 2005 -- will provide a definitive look the veiled surface, and astronomers can't wait.

"The radar data," Lorenz said, "suggest that on Titan itself, as well as in the terrestrial media, this event will make quite a splash."