Question: When a comet flies close to the sun on an elliptical obit around the sun does the comet give off any gas?, if so what gas?

Thomas Barrett answered on 18 Mar 2015:

Hey!

Have you heard about the Rosetta mission landing on a comet? I work with some of those people 😛 You may have seen Monica Grady on TV? She is my supervisor 🙂

Yes as a comet gets closer to the sun it begins to give of gas and dust. A comet has 2 tails – A dust tail of small, solid (and sometimes fluffy) particles . This tail forms because sunlight pushes on these small particles, gently shoving them away from the comet’s nucleus. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail.

A gas ion tail forms when ultraviolet sunlight rips one or more electrons from gas atoms in the coma (comet’s tail), making them into ions (a process called ionization). The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower.

Both types of tails may extend millions of kilometers into space. As a comet heads away from the Sun, its tail dissipates, its coma disappears, and the matter contained in its nucleus freezes into a rock-like material.

We are now beginning to understand the composition of the gas from 67/p the comet Rosetta is orbiting. The dueterium (heavier 2H) to hydrogen ratio (directly relevant to me as this is what I work on in space rocks) of the gas tail is about 3 times that of earths. So our water couldn’t have come from a comet like 67/p. The other stuff that has been detected is organic material but I can’t talk about what type as it is not published science yet!

So watch out for Rosetta news as there is a big conference on right now in the US and the Rosetta team are talking about new results!