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Chronicling a bold voyage of discovery—the Cassini/Huygens mission to Saturn and its enigmatic moon Titan—"Voyage to the Mystery Moon" delivers striking images of these fascinating planetary bodies nearly a billion miles from Earth. Saturn's broad rings hold myriad mysteries, and Titan, whose soupy atmosphere is similar to the one that enshrouded our planet billions of years ago, may hold clues to the origins of life. In hopes of answering some long-standing astrophysical questions, teams from NASA and the European Space Agency gamble years of effort to both ease the Cassini spacecraft into a workable orbit around Saturn and land the Huygens probe on Titan's never-before-seen surface.
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Saturn is the sixth planet in order of distance from the Sun, and the second largest in our solar system. Saturn’s average distance from the Sun is 1,435 billion km (891.5 million mi), or about 9.59 astronomical unit (AU). An AU is equal to the average distance between the Earth and the Sun, or 150 million km (93 million mi). The diameter of Saturn is about 121,000 km (75,000 mi), and its mass is equal to the mass of about 95 Earths, making it the second largest planet in our solar system after Jupiter.
The Romans named the planet after their god of agriculture. Saturn's most distinctive feature is its ring system, which was first seen in 1610 by Italian scientist Galileo, using one of the first telescopes. He did not understand that the rings were separate from the body of the planet, so he described them as handles (ansae). The Dutch astronomer Christiaan Huygens was the first to describe the rings correctly. In 1655, desiring further time to verify his explanation without losing his claim to priority, Huygens wrote a series of letters in code, which when properly arranged formed a Latin sentence that read in translation, “It is girdled by a thin flat ring, nowhere touching, inclined to the ecliptic.” The rings are named in order of their discovery, and from the planet outward they are known as the D, C, B, A, F, G, and E rings. These rings are now known to comprise more than 100,000 individual ringlets, each of which circles the planet.
Saturn has 47 moons. They range up to 2,575 km (1,600 mi) in radius. They consist mostly of the lighter, icy substances that prevailed in the outer parts of the gas and dust nebula from which the solar system was formed and where radiation from the distant Sun could not evaporate the frozen gases. The discovery of 12 of Saturn’s moons was reported as recently as May 2005. These moons are irregular in shape and small, ranging in diameter from 3 km (2 mi) to 7 km (4 mi). All but one orbit Saturn in a direction opposite that of Saturn’s larger moons, suggesting that these recently discovered satellites were originally asteroids that were captured by Saturn’s gravitational field.
The five larger inner satellites—Mimas, Enceladus, Tethys, Dione, and Rhea—are roughly spherical in shape and composed mostly of water ice. Rocky material may constitute up to 40 percent of Dione's mass. The surfaces of the five moons are heavily cratered by meteorite impacts. Enceladus has a smoother surface than the others, the least cratered area on its surface being less than a few hundred million years old. The detection of geysers on Enceladus suggests that liquid water below the surface is being heated as a result of tidal forces—the gravitational pull of Saturn and other moons. These tidal forces cause friction that heats rocks within the interior of the moon. The Cassini spacecraft detected oxygen atoms in the geyser plumes that jet out from the moon’s southern polar region. The plumes reach about 418 km (about 260 mi) into space. Scientists concluded that the geysers were spewing out water molecules that then broke down into oxygen and hydrogen atoms. Astronomers suspect that Enceladus supplies particles to the E ring, which neighbors Enceladus's orbit. Mimas, far from being smooth, displays an impact crater the diameter of which is one-third of the diameter of the satellite itself. Tethys also bears a large crater and a valley 100 km (62 mi) in width that stretches more than 2,000 km (1,200 mi) across the surface. Both Dione and Rhea have bright, wispy streaks on their already highly reflective surfaces. Some scientists conjecture these were caused either by ice ejected from craters by meteorites, or by fresh ice that has migrated from the interior.
Titan is the largest moon of the planet Saturn and the only moon in the solar system with a dense atmosphere. Scientists think Titan may provide important clues about conditions on the primitive Earth, and even how life began. Titan is spherical, measuring about 5,150 km (about 3,200 mi) in diameter, larger than the planet Mercury. It is the second largest moon in the solar system, after Jupiter’s moon Ganymede. Saturn’s first moon to be discovered, Titan was found in 1655 by Dutch astronomer Christiaan Huygens. A space probe named for Huygens landed on the surface of Titan in 2005. The moon is named after the Titans, a family of giants in Greek mythology.
The Cassini and Huygens probes have revealed a geologically young surface on Titan, with few visible impact craters. The features seen so far appear to be formed from dirty water ice overlain mainly by organic (carbon-containing) deposits. The moon’s surface temperature is a frigid -178°C (-289°F). At such temperatures water ice probably plays a role very similar to silicate rocks on Earth and makes up the moon’s crust. The organic deposits form highlands and dunes, and may coat flat plains. In some cases the dunes are as high as 100 m (330 ft) and stretch for as long as 1,500 km (930 mi), running parallel to each other like those in the Sahara desert on Earth. The terrain is rugged and shows evidence of erosion from methane rain and from liquid seeping from underground. The rocklike ice chunks on the surface, photographed by Huygens, have a rounded shape that could result from their tumbling in flash floods. Scientists have also identified possible cold volcanoes that may spew a mix of ammonia and water ice. Titan is Saturn’s densest moon. Planetary scientists theorize that Titan has a rocky core about 3,400 km (about 2,100 mi) in diameter, surrounded by ice. Some researchers think an underground ocean of liquid water may surround the ice. Above this possible ocean is the moon’s crust, made of solid ice.
Titan - What We Know:
Titan is the only moon in the solar system with a thick atmosphere surrounding it.
The atmospheric pressure near Titan's surface is 60% greater than Earth at sea level.
The atmospheric temperature near Titan's surface is 95K (-178 C or -288 F).
As on Earth, the most abundant gas in Titan's atmosphere is nitrogen.
Methane is the second most abundant gas; more than a dozen other gases are present.
The thickness (extent) of Titan's atmosphere is about 10 times that of Earth.
A thick haze at 200 km (120 mi) altitude hides Titan's surface at visible wavelengths.
Titan's diameter is 5150 km (3200 mi), about 40% as large as Earth.
Titan is the second largest moon in the solar system; only Jupiter's Ganymede is larger.
Titan and Ganymede are both larger than the planets Mercury and Pluto.
Titan apparently keeps its same face toward Saturn as it orbits the planet.
Titan orbits Saturn at a distance of 1,221,830 km (759,210 mi) from Saturn's center.
Titan orbits Saturn in just under 16 days (orbital period = 15.9454 days).
Oceans (or lakes) of liquid ethane may cover a large fraction of Titan's surface.
Titan's surface is non-uniform at radar wavelengths.
Titan has a surface feature (continent?) that is bright at infrared wavelengths.
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