Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: bizerl on 18/03/2013 01:06:54

Title: What comes first? The comet or the tail?
Post by: bizerl on 18/03/2013 01:06:54

I'm led to believe that the comet's tail is caused by the solar wind heating the surface and turning the ice into vapour. The pop-culture view is that of a tail streaming out behind a comet as it hurtles through space.

Now, this seems obvious while the comet is heading towards the sun, but what happens when it is on it's way back to the outer solar system? Is the tail still behind the comet's direction of travel, or does it continue to be pointing away from the sun, in which case, the comet would actually be travelling through it's own tail?

Title: Re: What comes first? The comet or the tail?
Post by: David Cooper on 18/03/2013 18:19:19

The tail points away from the sun, so the comet follows its tail on the way back out, but the comet doesn't go through its tail as the tail is always moving away from it - it's all caused by the solar wind pushing it away from the sun. There can also be two tails pointing in slightly different directions, one mostly containing gas and pointing more directly away from the sun while the other with more solid material in it doesn't accelerate so readily so its original momentum in the direction the comet is moving shows up more.

Title: Re: What comes first? The comet or the tail?
Post by: evan_au on 18/03/2013 20:18:22

Solar radiation (photons) and solar wind (mostly protons & electrons) both play a role in heating the comet, and imparting momentum to the gas boiling & dust floating off the comet's head.

At a speed of 400-700 km/second, the speed of the solar wind exceeds the velocity of a comet near Earth's orbit (and light always exceeds the velocity of the comet), thus blowing the gas away from the Sun faster than the comet is traveling away from the Sun.

Title: Re: What comes first? The comet or the tail?
Post by: Lmnre on 19/03/2013 13:33:50

I searched for an illustration, and I found that comets can have two "tails", gas and dust.

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fspaceplace.nasa.gov%2Ftails-of-wonder%2Fcomet_diagram.en.gif&hash=a7918c49ef3b1e0b7b750541e14d1853)

source (http://spaceplace.nasa.gov/tails-of-wonder/)