by Master Chia

Saturn is the second largest planet in the Solar System, named after the Roman god of agriculture. It orbits the Sun every 29.5 Earth years at an average distance of 9.5 AU. Its best-known feature is its series of rings, discovered by Galileo in 1610, which arc made up of small icy chunks (mostly just a few centimeters across).

One of the ‘gas giants’, it is primarily composed of hydrogen and helium. Aurorae occur on ail planets with a magnetic field, including the Earth. Charged particles such as electrons and protons from the highly energetic solar wind are channeled downwards by the planet’s magnetic poles, and collide with gas molecules in the atmosphere, causing them to emit radiation and giving rise to spectacular luminous curtains. On Earth, these arc occasionally visible, even from middle latitudes: the Aurora Boreahs around the north pole and the Aurora Ausiralis in the south, in the Saturnian atmosphere, however, most of the gases (mainly hydrogen) radiate in the ultraviolet region of the spectrum, invisible to ground-based instruments because most ultraviolet radiation does not penetrate the Earth’s atmosphere. The FIST’S ultraviolet capability enabled pictures to be taken of the aurorae a; Saturn’s north and south poles. The top picture, taken in ultraviolet light, clearly shows the aurora at Saturn’s north pole. The ‘aural curtain’ of light pushes as high as 2000 km above the tops of the Saturnian clouds. Even though Saturn’s south pole is hidden from view, the south aural display is just visible around the edge of the planet. The curtain varied rapidly during the time of the observations, but the brightest point always stayed at a set angle from the Sun. The bottom picture shows Saturn in visible light, and the differences are striking. Ultraviolet sunlight is reflected from higher in the Saturnian atmosphere than visible light. The parts from which ultraviolet light is reflected do not contain the banding and structure present in the lower atmosphere, giving Saturn a featureless appearance in the higher frequency ultraviolet. Also present in visible light- is a huge white storm system near the equator which the HST was able to track while it raged.