Saturn looms large in the sharpest colour image yet taken of the planet by the approaching Cassini-Huygens spacecraft, due to arrive at the Ringed Planet on 1 July.
The image was taken when the bus-sized Cassini probe was over 56 million kilometres away from Saturn 鈥� a third of the distance between the Earth and the Sun. It is a composite of several exposures taken on 8 March and was released on Friday.
Even from this distance, some intriguing features can be seen. These include two small, grey, faint spots just visible at a latitude of about 40 degrees in Saturn鈥檚 southern hemisphere. Saturn is about 10 times as wide as Earth, and the spots appear to be slightly smaller than our Moon.
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鈥淭hey鈥檙e probably storm systems in the atmosphere,鈥� says Fred Taylor, a planetary scientist at the University of Oxford, UK. 鈥淭he Hubble Space Telescope did see some storms whose duration was on the order of months,鈥� he told New 杏吧原创.
However, unlike Hubble, Cassini will be able to follow the storms more or less continuously once in orbit, which will help understand the transient phenomena. 鈥淲hat we鈥檙e after is meteorology on a completely different planet than Earth, but with all the same physics,鈥� he says.
Two of Saturn鈥檚 31 moons, Mimas and Enceladus, also appear in the image as pinpoints of light.
Rings and fields
The Cassini mission, launched in 1997, has flown twice around the Sun, getting 鈥済ravity assists鈥� from Venus, Earth, and Jupiter along the way. It will enter orbit around Saturn on 1 July, when it will start four years of data collection on Saturn鈥檚 atmosphere, rings, magnetic fields, and moons.
鈥淭he real excitement鈥檚 still to come,鈥� says Taylor. Planetary scientists hope to tease apart the Solar System鈥檚 history by comparing the composition of the giant planets Saturn and Jupiter. The latter was extensively studied by NASA鈥檚 14-year Galileo mission.
They also hope to understand mysterious features such as the coloured bands in Saturn鈥檚 atmosphere, which are more numerous and narrower than Jupiter鈥檚. The bands are probably wind currents in the atmosphere, but their different colours may signal different compositions.
On 25 December 2004 Cassini will release the 320-kilogram Huygens probe, which will parachute into the thick, murky atmosphere of Saturn鈥檚 giant moon Titan three weeks later.
The probe will sink through the haze for about two hours, measuring the atmosphere鈥檚 composition and snapping pictures along the way. It may also continue to take data from the surface, but for no longer than 30 minutes.