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Exploring Saturn and Titan

A billion miles out from the sun – 10 times farther than Earth – lies a world we’ve yet to explore.

Galileo Galilei was the first to turn a telescope to Saturn, in 1610; the planet, he found, “bulged.”

Half-a-century later, with a much better ‘scope, Giovanni Cassini resolved the “bulges” into a planet-encircling ring. Cassini also discovered that Saturn did not orbit the sun alone – it was accompanied by a moon, which he named Titan.



Early 20th century astronomers determined that Titan was huge – larger than the planet Mercury. And by mid-century, they knew that Titan had an atmosphere.

The robot explorer Voyager 1 reached Saturn and Titan in 1980, radioing back our first-ever close-up view of Titan. It looked like a featureless, orange ball.




The sun’s ultraviolet (UV) radiation promotes cancer by breaking the bonds that hold DNA together.

Fortunately, most solar UV expends its energy dozens of miles overhead as it breaks the bonds that hold oxygen molecules together. When the broken molecules recombine, they form ozone, which absorbs even more UV.

At a billion miles out, it takes about an hour for sunlight to reach Saturn, where it’s barely strong enough to raise Titan’s surface temperature much over 300 degrees below zero (Fahrenheit). But the sun’s UV is still strong enough to bust up molecules.

Titan’s atmospheric chemistry is different from Earth’s: Instead of forming ozone, the busted-up molecules recombine to create the orange haze that fills its upper atmosphere – and obliterates our view.

Stained glass absorbs most colors of light, but not all – some colors get through, giving the glass its color.

The haze in Titan’s atmosphere blocks pretty much all colors of visible light, but other colors make it through – invisible colors that only our instruments can see.

Observing in haze-piercing infrared and radio wavelengths, astronomers have seen Titan’s surface.

Some areas are brighter; some are darker. But what are these bright and dark areas – continents of water ice?

Rivers and lakes of liquid ethane (like gasoline, but thinner)? Glaciers of frozen propane?

In 1997, Earth launched a spacecraft – “Cassini” – toward Saturn. Arriving this past summer, Cassini injected itself into orbit and began radioing back infrared and radar images that are clearer and more detailed than any we’ve seen before. Bright and dark regions leapt out at the eye.

But we still don’t know what they are.

Cassini did not go to Saturn alone. A saucer-shaped spacecraft built by the European Space Agency has been riding piggy-back on Cassini, locked to the mother craft by explosive bolts.

Three weeks ago, a jolt of electricity detonated the explosives; the bolts disintegrated, and the two spacecraft sprang apart. The hitchhiker, named for 17th century astronomer Christian Huygens, began a three-week solo journey. Early this morning, Titan’s gravity will have pulled Huygens into its atmosphere.

Hitting the atmosphere at 14,000 miles an hour, Huygens squeezed and heated the air to incandescence as its saucer shape slowed it to less than a thousand miles an hour. Parachutes slowed the craft yet more.

It would then analyze Titan’s atmosphere – an atmosphere similar to Earth’s when life first evolved on our planet.

Once below the haze layer, Huygens should have recorded what the surface of Titan really looks like.

Huygens was not designed to survive a landing, but it might. If it were to splash down (rather than land) in a hydrocarbon lake, it would float.

At 7 p.m. on Saturday, Jan. 29, come join us at the old Nevada City airport, where some friends and I will set up telescopes to observe the stars, the rings of Saturn and Titan.

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Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesday on KVMR-FM (89.5).


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