Looming like a giant flying saucer in our outer solar system, Saturn puts on a show as the planet and its magnificent ring system nod majestically.



Looming like a giant flying saucer in our outer solar system, Saturn puts on a show as the planet and its magnificent ring system nod majestically.




When the clock strikes midnight on Dec. 31, heralding the start of 2004, dash outside and look up. Directly overhead you'll see a yellow star outshining the others around it. That star is a planet: Saturn, having its closest encounter with Earth for the next 29 years.


"Saturn's going to be really beautiful," says NASA astronomer Mitzi Adams. "Not only will Saturn be about as close to Earth as it can get -- 1.2 billion kilometers (748 million miles) away--but also its rings are tipped toward us. Sunlight reflected from Saturn's rings makes the planet extra bright."


If you have a telescope, advises Adams, be sure to point it at Saturn. Even a small 'scope will reveal the spectacular rings. "They're breathtaking," she says.


2004 is going to be a big year for Saturn. The Cassini-Huygens spacecraft, en route since 1997, will arrive there in June. Other spacecraft have visited Saturn -- Pioneer 11 and the Voyagers -- but they merely flew by, taking hurried pictures during encounters that lasted little more than days. When Cassini reaches Saturn it will stay, orbiting and studying the planet for at least four years.


Saturn is a world of great mystery. Consider its rings: Researchers aren't sure what made them or when. Some evidence suggests that the rings are young -- only a few hundred million years old. If so, they first encircled Saturn at about the same time dinosaurs took over the Earth. In the cosmic scheme of things, this is recent history.


Saturn's rings might be collapsing just as fast as they formed -- so say some theorists. Small moons orbiting through the outermost regions of the ring system are gaining angular momentum at the expense of the rings, a result of gravitational interactions between the moons and chunks of ring-matter. During the next few hundred million years, the outer half of the rings could sag toward the planet as the little moons (called shepherd satellites) are flung away. Saturn will look much less impressive after that.


Could it really happen? Cassini will gather the data scientists need to answer that question and many others about Saturn's rings, moons, weather and magnetism. There's much to learn about this distant planet.







A Hubble Space Telescope image of Titan.
A Hubble Space Telescope image of Titan. The bright area (about the size of Australia) might be a continent, an ocean, an impact basin. No one knows.







At least as intriguing as Saturn is its giant moon Titan.
"You can see Titan through a telescope--an 8th magnitude "star" a few ring-diameters from Saturn, moving from night to night as it orbits the planet," notes Adams. Titan is bigger than Mercury and Pluto, and it has an atmosphere 60 percent denser than Earth's. In other words, Titan is a full-fledged world. If it orbited the sun it would surely be considered a planet.


The curious thing about Titan is how little we know about it. It could be teeming with life or peppered by ruins from ancient civilizations, and we wouldn't know because Titan is completely covered by thick orange clouds. A camera onboard the Hubble Space Telescope has been able to see through them, to a degree, by observing at infrared wavelengths. The images hint of continents and seas, but Titan is so far away even Hubble can't take a clear picture of it.


In January 2005, the European Space Agency's Huygens probe will finally enter Titan's clouds to find out what lies underneath. This could be one of the most exciting moments in solar system exploration -- ever. Huygens will take more than 1,100 images during its two and a half hour descent by parachute. Scientific instruments will sample Titan's atmosphere, gauge its winds, and--if the probe survives landing--measure the physical properties of the ground.


Huygens probably won't find evidence of life, at least not life as we know it. Titan is too cold. Its surface temperature, researchers estimate, is minus 178 Celsius (289 Fahrenheit below zero). This doesn't mean life is impossible, though. Titan's atmosphere is rich in organic compounds: ethane, methane, hydrogen cyanide and others. The low temperature of the moon encourages ethane and methane to liquefy, so there might be puddles, lakes or even oceans of liquid hydrocarbons sloshing around on the surface. Perhaps these are places where organic molecules get together for the first stirrings of simple life.


The truth is, no one knows what Huygens will find. Or Cassini. And that's what makes exploration fun--something worth pondering this New Year's Eve. At the stroke of midnight. Looking up at a world of mystery.


Written by Dr. Tony Phillips, Science@NASA, NASA's Marshall Space Flight Center.