17-05-2008 Titan – lifting the veil (Article 137)

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Simon Kenny
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17-05-2008 Titan – lifting the veil (Article 137)

Post by Simon Kenny » Wed Dec 31, 2008 10:52 am

Titan — lifting the veil. (Article 137)

In March, 1655, Christiaan Huygens, a Dutch astronomer, pointed his telescope to the planet Saturn in search of orbiting moons. Inspired by the discoveries of Jupiter’s moons, Huygens found his objective: a tiny speck of light regularly circling its massive parent planet. He gave it the Latin title ‘Saturni Luna’ (Saturn’s moon). As other moons were discovered, notably by Italian astronomer Giovanni Cassini, the moons were given numbers. Titan was designated Saturn IV. As discoveries continued, this naming system became confusing. In 1847, John Herschel, son of astronomer William Herschel, renamed the largest moon Titan, after the legendary children of the god Uranus and the earth goddess Gaia.

Until recent times, little was known about Titan. Its dense, hazy atmosphere, made telescopic study of its surface impossible and exact estimates of its diameter untrustworthy. For some time before the Voyager space probes, Titan was considered the biggest natural satellite in the Solar System, narrowly beating Jupiter’s Ganymede into second place. However, in 1980, Voyager I found that Titan’s dense atmosphere had made it look bigger than it really was in earth-bound telescopes. Its diameter is 5150 km, over 100 km less than Ganymede. While its diameter is about 270 km greater than Mercury, the Sun’s innermost planet, Mercury’s large iron core makes it far more massive.

The arrival of the Cassini-Huygens mission to the Saturn system in 2004 has revealed a wealth of new knowledge, especially about Titan. The appropriately named Huygens probe detached from the main craft and coasted to a rendezvous with Titan on January 14th 2005. It landed in a bright area about the size of Australia, called Xanadu and in ninety hectic minutes, Huygens returned a wealth of data about Titan’s atmospheric makeup, its winds, surface features and ground composition. Aerial photos from the descent show highlands intersected by river-like channels that combine and head towards dark low-lying areas, resembling seas. Titan’s frigid minus 180ºC temperatures show that water isn’t the eroding factor here. The liquids are more likely to be hydrocarbons like methane that liquefy at these temperatures. The dark surface of Titan made imaging difficult, described as like ‘photographing an asphalt car park at dusk’. Still, high quality pictures were returned, including a memorable one of the surface receding from Huygens’ landing spot. It consists of a dark-brown, flat, sand-like surface, apparently strewn with heaps of pebbles, stretching to a curved, clouded horizon. Subsequent studies suggested Huygens may have landed near the edge of a large hydrocarbon lake.

Meanwhile, Cassini is currently busy lifting the veil of mystery by taking radar images of Titan’s surface from space through its dense nitrogen atmosphere. It has recently discovered what may be methane ‘seas’ near its North and South poles, the first confirmation of large liquid reservoirs outside planet Earth. Titan’s dense atmosphere and hydrocarbon lakes are understood to resemble infant Earth, about four billion years ago. Could Titan harbour the beginnings of life? The investigations continue.

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