I understand that the solid gas coating the nucleus of a comet is melted and that this gas is ionised by the UV rays from the sun. This makes the gas particles charged.

What I dont understand is why they are always pointing away from the sun. I agree that they would be affected by magnetic fields, however I dont see why this means they follow a path away from the sun. Magnetic fields provide a force perpendicular to the direction of motion, not a long it. I've seen several explanations on other websites where they give a vague description as the gas is being carried by the solar winds along the suns magentic field lines, but I dont understand how this is possible.

Can someone please clarify why the ion tail of a comet always points away from the sun?

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    $\begingroup$ The Wikipedia article discusses this. Also see the linked general article on magnetospheres. $\endgroup$ – PM 2Ring Mar 24 at 17:17
  • $\begingroup$ What's your objection to the gas is being carried by the solar winds along the suns magentic field lines? Relatively speaking, there's a lot of kinetic & magnetic energy in the solar wind, particularly close to the sun. True, it's not very dense, but neither is the gas in a comet's tail. $\endgroup$ – PM 2Ring Mar 25 at 8:04
  • $\begingroup$ My objection is that unlike an electric field, the force applied by a magnetic field on charges is not along the field lines. The charges would have a force applied to them that is perpendicular to the direction of the field. So I don't understand how they move along the field lines if they are always receiving a force perpendicular to them. $\endgroup$ – Vishal Jain Mar 25 at 11:20
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    $\begingroup$ Ah, ok. The charged particles can move along the magnetic field lines in a helical trajectory. feynmanlectures.caltech.edu/II_29.html $\endgroup$ – PM 2Ring Mar 25 at 11:55
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    $\begingroup$ The curvature of the helices is pretty tight. See physics.stackexchange.com/a/311847/123208 $\endgroup$ – PM 2Ring Mar 25 at 14:39

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