A powerful, five-month-long storm continues to rage on Saturn, making it the planet鈥檚 longest continuously observed tempest. 快猫短视频s suspect the storm ultimately draws its amazing power 鈥� producing lightning bolts 10,000 times as strong as those on Earth 鈥� from the planet鈥檚 own internal heat.
The Cassini spacecraft has previously observed lightning storms on Saturn in 2004 and 2006, but those lasted for less than a month.
Before that, NASA鈥檚 two Voyager spacecraft each spent a few days listening to radio emissions from lightning storms during flybys of Saturn in 1980 and 1981. The flybys were spaced about nine months apart, so it is possible that the emissions came from a single storm that seethed for nearly a year.
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But because the Voyagers did not track the storms over time, it is impossible to say for sure. 鈥淔rom this point of view, [this new storm] is the longest lightning storm we鈥檝e ever seen,鈥� says Georg Fischer, a member of Cassini鈥檚 radio and plasma wave science team at the University of Iowa in Iowa City, US. 鈥淚t hasn鈥檛 stopped 鈥� I look at it every day.鈥�
Radio emission from the storm was first observed on 27 November 2007, and about a week later, Cassini鈥檚 cameras spotted complex, rotating storm clouds 鈥� thought to be made of water 鈥� that had risen above the planet鈥檚 ammonia cloudtops.
The electrical storm takes up the same volume of space as the Earth鈥檚 troposphere, the region of the atmosphere from the surface to an altitude of about 15 km, where weather occurs. 鈥淚t鈥檚 absolutely huge,鈥� Fischer told 快猫短视频. 鈥淚magine you have lightning on Earth everywhere 鈥� that鈥檚 how you could compare it.鈥�
The storm has continued for five months, though with varying strength. 鈥淚t waxes and wanes,鈥� Fischer says. 鈥淚t seems that every 10 to 14 days there鈥檚 a kind of enhancement, then for one week to 10 days, it is less intense.鈥�
Violent updrafts
The reasons for this variation are not clear 鈥� the storm actually originates too far below the planet鈥檚 gaseous 鈥榮urface鈥� to observe. Modelling suggests that temperature differences at a depth of about 200 to 300 kilometres might provide the trigger. Sunlight does not penetrate to such depths, suggesting it is the planet鈥檚 own internal heat that is somehow responsible for the temperature differences.
The storm鈥檚 location may aid and abet its survival. It occurs at a latitude of about 35掳 in the planet鈥檚 southern hemisphere 鈥� a region dubbed 鈥楽torm Alley.鈥� At that location, Saturn鈥檚 atmosphere circles the planet more slowly than in other bands. That may allow the storm clouds to remain intact as they ride violent vertical winds, or 鈥榰pdrafts鈥�, from their source deep within the planet鈥檚 atmosphere up to the surface.
鈥淚t鈥檚 a very unique location 鈥� it seems at Saturn, lightning storms cannot actually happen everywhere,鈥� says Fischer.
Shaded belt
The only other place on Saturn that similar storms have been observed is the equator, which is where the Voyager spacecraft observed them. In that case, sunlight may have played a role in powering the storms.
That鈥檚 because at that time, the Sun hit the rings nearly edge-on, keeping Saturn鈥檚 equator constantly shaded. The drastic temperature difference between the cool, shaded equatorial belt and the surrounding Sun-kissed areas may have fuelled regular convection patterns that drove the storms.
In September 2009, the planet鈥檚 orientation will be the same as it was during the Voyager flybys, with the rings casting a shadow over the equator. 鈥淲e鈥檒l see if we have the same storms,鈥� says Fischer. 鈥淭hat鈥檚 why it鈥檚 important to have an extension of the Cassini mission, which was just now approved. You can only watch these things when you are there for a long time.鈥�
Cassini: Mission to Saturn 鈥� Learn more in our continually updated .
