Thursday, August 14, 2008

Enceladus Flyby


The excitement in Southern California was palpable. Monday August 11 our Cassini spacecraft made another close flyby of Enceladus' South Pole. The spacecraft also recorded occultations of light from the star zeta Orionis. By combining stellar occultation data with photos, we can get precise locations of the geysers. Upper photo shows Damascus Sulcus, one of the "tiger stripes" at resolution of 24 meters/pixel.

In the graphic below, the blue line is the path of starlight from zeta Orionis. Interruptions of starlight are labelled a, b, c,... Roman numerals are gas jets found in photographic images, which closely correspond with the stellar occultations. The sources of the jets are less than 300 meters across. Data indicates that the jets are blasting off with velocities greater than 600 m/sec. The surface is strewn with huge ice boulders, apparently throw off by the jets.

As readers of this blog know, Saturn and Enceladus are subjects of intense study. One of the first posts back in June 2006 was about Enceladus internal heat.

"In 2005 our Cassini spacecraft made some amazing discoveries about Saturn and her moons. The moon Enceladus has a volcanic "hot spot" centred on its South Pole. The pole, which should be the coldest region on the moon, is the hottest! This spot emits an enormous plume of vapour which maintains Saturn's E Ring. Old theories of radioactive decay or tidal stress can not explain this hot spot.

"Enceladus' core and behaviour can be modelled with a central singularity of 10^12 kg. This mass is typical for a primordial singularity. This object consumes only 2.8 kg per year and generates 10^9 watts of radiation. Water and other molecules near this centre are heated to a plasma. Electrons are stripped from atoms, and the resulting ions are drawn into circular orbits. The resulting current generates a magnetic field with the "positive" pole in the South.

"Electrons and positively charged ions spiral along magnetic field lines to form bipolar jets, the classic sign of a singularity. The Northern jet is composed of electrons which are absorbed by the moon's interior. More energetic ions of the Southern jet penetrate these layers to warm the South Pole. Escaping ions spiral into space, exactly as observed by Cassini.

"Unless Saturn's Rings are replenished, they would decay within 100 million years. Then we would face the anthropic question of why they exist in the right time for humans to view them. Thanks to the Cassini spacecraft, we have witnessed the E Ring being resuppllied from a moon. This observation suggests that similiar processes maintain the rings indefinitely.

Back in December 007, the AGU meeting included a short talk by scientist Jennifer Meyer. The young woman asserted that Enceladus' 6 GW of heat can not be accounted for by tidal forces. The conventional estimate from tidal heating is only 0.12 GW. The old hypothesis or "radioactive decay" does not work for these icy moons. Why do so many worlds have hot spots on their poles?

On October 9 Cassini will make its closest flyby, passing only 25 km from Enceladus! Already the spacecraft has found tantalising data and spectacular photos. Little Enceladus could hold wonders not yet imagined. It could even hide a small Black Hole.

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1 Comments:

Anonymous Anonymous said...

Quote; "Why do so many worlds have hot spots on their poles?"
So... what other worlds does the writer refer to?

Is it possible that Enceladus' south polar hot spot is due to electrical inductance heating? Consider; Interior to Enceladus, perhaps there is some (poorly) conducting material that generates an electrical current as it slices through Saturn's magnetic fields.

But I suppose I would'nt mind seing a primordial black hole either.

12:37 PM  

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