Saturn Spectacular
Solving the puzzles of the ringed planet
A
A. In 1610 the Italian astronomer Galileo pointed his crude telescope at the planet Saturn and was dumbfounded by what he saw: "The planet Saturn is not alone, but is composed of three, which almost touch each other, and never move or change with respect to one another." Even more surprising, the two bulging planets on either side of the main planet had disappeared when he looked again a few months later. Eventually, the frustrated Galileo decided never to look at Saturn again. Now, of course, we have much better telescopes, and we know that Galileo was looking at the planet's unique set of wide, thin rings. Seen broadside, they resembled companion planets through Galileo's weak lenses; later, seen edge-on, they shrank to nothingness. But nearly 500 years after Galileo's observations, Saturn still teases astronomers. Saturn's magnificent rings, for example, consist of trillions of pieces of ice, some no bigger than a speck of dust. The ring particles are so small that they could be expected to scatter and fall into the planet, yet they are still there. Scientists are unsure about the origin of the rings, their exact chemical composition, and why they behave in the way that they do.
B
B. However, as spectacular as Saturn's rings are, the fuzzy orange ball of Saturn's giant moon Titan is even more interesting. Although it is larger than the planet Mercury, Titan probably resembles other large moons in the Solar System. It is a rock covered with ice and dirt. However, it has something no other moon has: a substantial atmosphere whose pressure is 50% greater than Earth's. Even more intriguing, Titan's atmosphere consists mainly of nitrogen (the primary component of our own air), mixed with carbon-based compounds. Cloaked in this atmosphere, Titan's surface may resemble the surface chemistry of the early Earth, but astronomers cannot see through the moon's maddeningly opaque orange fog.
C
C. All sorts of Earth-like chemical interactions could happen on Titan. Scientists hesitate to speak of the possibility of life when they speak of Titan, but it is a distant possibility. Living on Titan would be no walk in the park. From the vantage point of the Saturn system, the sun is a rather dim bulb. Titan is therefore a very cold place. Surface temperatures average about -300 degrees Fahrenheit. At those temperatures, water is a rock and would flow only from volcanoes. Although Titan is half water, there is nowhere to get a drink. In addition, there is no oxygen in Titan's atmosphere-it is all locked up in water ice. The only hope for life as we know it, and it is an exceedingly slim one, is that water mixed with ammonia may get warm enough deep below the surface to liquefy. If so, life could possibly eke out an underground living much like the hardy microbes that surround Earth's hydrothermal vents (deep cracks on the seabed through which boiling water and hot gases escape).
D
D. Titan could contain information on the prebiotic chemistry that led to life on Earth and perhaps elsewhere in the Universe. The bitterly cold temperatures that make Titan so forbidding for life in some ways make it more intriguing. Titan's chilly climate keeps things in a state of preservation, so that it can hang on to most of the substances that it has acquired during its 4.5 billion years in the Solar System. The organic reactions that may have established the starting conditions for life on the early Earth are long gone, erased by our planet's high-speed chemical and geologic evolution. On Titan, similar reactions may still be sitting in deep storage.
E
E. Measured against its showy rings and haze-obscured moon, Saturn itself seems dowmight ordinary. Yet the 75,000-mile-wide planet-the second largest in the Solar System-holds some serious interest of its own. Like the planet Jupiter, Saturn is a gas giant: a relatively small ball of rock surrounded by a vast envelope of helium, hydrogen, and various hydrogen compounds. Saturn is only half as dense as Jupiter, even less dense than water. It releases less heat than Jupiter, but, given its smaller size, scientists are not sure why it radiates any heat at all. Saturn's storms are, surprisingly, more powerful than Jupiter's, and its jet streams are much faster. The planet looks blander, however, because a thick haze of ammonia crystals obscures the colorful banding seen so easily on Jupiter.
F
F. Scientists hope that studying these differences will reveal how giant planets form, how weather systems work under different conditions, and what planets around other stars might be like. A recent spacecraft that investigated Saturn and Titan (the Cassini-Huygens probe) has produced results that Galileo would have dearly appreciated back in 1610: photographs that finally show Saturn with crystalline clarity. After all the data from Cassini-Huygens has been interpreted, even though that might take 40 years, all questions on these topics may have been answered once and for all.
1.
Paragraph A
A longstanding puzzle
List of Heading
Comparing two planets
A surprisingly small moon
A longstanding puzzle
Saturn’s fascinating moon
The importance of Titan's gravity
Expectations of possible solutions
The problems for life on Titan
An advantage of the low temperatures
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