Rings and wings

Information gathered by the spacecraft Cassini may solve many riddles about the next-most interesting planet after Mars

Published: Saturday 15 November 1997

All fired up: Cassini takes a< (Credit: Ap / pti</font)the launch of Cassini, which will visit Saturn, is another major event in space exploration in this decade. The probe, part of a project that began almost 13 years ago, took off on October 13, 1997, and will reach Saturn in about seven years. Its mission: getting detailed information about the planet and its satellites. The spacecraft will spend four years orbiting Saturn.

Named after 17th century Italian astronomer Giovanni Cassini, who first discovered and named Saturn's mysterious moon Iapetus, Cassini is the last of the large multi-purpose probes that were launched in the 1980s. Unlike other large spacecraft previously launched -- Voyager 2, for instance, which sent in the first fuzzy close-up pictures of Saturn's rings and satellites -- Cassini is better equipped. Standing 7 metres (23 feet) tall, it carries 12 'packages' of scientific instruments plus another probe, Huygens, which will be dropped on to Titan, Saturn's largest moon. Huygens carries six more fancy sensors that will provide details about Titan.

One of the major mysteries Cassini is expected to assist in solving is the dark side of Iapetus. Iapetus revolves around Saturn, much like the Earth's moon revolves around our planet, except that it takes 80 days to accomplish it. Unlike our moon, which has a dark side that never faces the Sun, Iapetus has a mysterious black patch. Many theories have been put forward to explain what this patch consists of and how it came to be on an otherwise brilliant white moon.

The centre of the elliptical patch is on the apex (as against the axis) of motion of the moon -- roughly, its equator -- and is so dark that 98 per cent of the light that falls on it is absorbed. Such a material is unusual, though not unknown in our solar system -- it has been observed in comets and meteors. But the material cannot be merely debris of a comet scooped up by Iapetus. What is more, a direct collision with the moon would have left a crater. But the black patch -- now called Cassini Regio -- is like a thick layer rather than a crater. So this explanation, too, is inadequate. There is another popular explanation, believed by science fiction enthusiasts -- especially those who saw the Arthur C Clarke picture 2001: A Space Odyssey . According to this explanation, the ring has been artificially created by aliens to attract the attention of humans. Unfortunately, the Voyager 2 images, though taken from a distance of about 500,000 miles (804,500 km) from Saturn, are clear enough to show that the material is not artificial. The mystery will probably be solved by information and photographs that Cassini will supply.

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