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Comet Encke

3 November 2015

A paper in the October 13th issue of the Astrophysical Journal used data from NASAs STEREO observatory to look at gusts of the solar wind interacting with the tail of Comet Encke, a short period comet, in order to study its visible variations and very high temperatures. We know that CME events can overload the atmosphere of the Earth with lots of temporary heat so I suppose the thinking here is that it is the heat of the solar wind gusts that causes the comet to react and sublimate. However, this is not actually stated but as the consensus view is that comets become more active as a result of coming closer to the heat of the Sun there is no reason not to think they have something similar in mind.

The solar wind as it reaches the top of the atmosphere is some 70 times hotter than one might expect of the solar corona, it is said, which is curious to say the least. In other words, it gets hotter as it travels through space. The source of the heat build-up is the mystery – and this is what has been solved, according to the authors.

It is known the solar wind contains electrically charged electrons and ions and is magnetic to boot, forging a magnetic connection between Sun and Earth (and any other planet or cosmic body in its path). There is no consensus on what is behind the wind acceleration, especially when it reaches high speeds. Scientists have studied the movements of hundreds of dense pieces of glowing ionised gas within the ribbon of the tail of Comet Encke. Fl;uctuations in the solar wind can be tracked in the tail, so they were able to reconstruct the motion of the solar wind, and what they was was turbulence. They went on to calculate that energy derived from turbulence was ten times what was required to heat the solar wind to observed temperatures – and this will no doubt end up embedded in the consensus. Turbulent motion mixes the solar wind leading to rapid variation in temperature as seen in movements observed by satellites above the Earth – so we can see why they wanted to clarify what they were recording.

The solar wind dominates the solar system and travels well past Pluto – thereby providing heat and magnetism to cosmic bodies in all corners of the helio-sheaf. All comets, when they approach the Sun, develop an ion  tail – caused by the solar wind (charged gas or plasma) and this excites vaporised material from the comet. The tail then follows the magnetic field embedded in the solar wind.

NASA news item.

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