[Swordmaker]

Let's see we've got coming out of Comet 67P/Churyumov-Gerasimenko:

• CH₄: Methane
• NH₃: Ammonia
• H₂O: Water
• HH₂: Acetylene
• HCN: Hydrogen Cyanide
• CO: Carbon Monoxide
• C₂H₆: Ethane
• CH₃OH: Methanol
• H₂S: Hydrogen Sulfide
• CO₂: Carbon Dioxide
• OCS: Carbonyl Sulfide
• SO₂: Sulfur Dioxide
• CS₂: Carbon Disulfide

All of which is quite a stew only about 3.3% is water. I repeat, where's the dirty snowball?

[Boogieman]

Lots of Hydrogen Sulfide. That is one stinky comet!

More like a rotten egg than a dirty snowball :)

[Swordmaker]

I think that what is occurring is what little H₂O they are encountering in the coma/atmosphere of 67P//Churyumov-Gerasimenko is entirely created by the negatively charged Hydroxyl radical OH being ejected along with all those other gases and then encountering the positively charged ionized free Hydrogen radical H+. "This wind consists primarily of protons, the positively charged nuclei of hydrogen atoms"—space.com.

They want to be balanced with a negatively charged something or other. . . and the most active in the area is the negatively charged Hydroxyl radical OH!

These will attract each other and naturally collide and combine, emitting energy in the form of light photons creating a glow discharge in the process!

H+ —> OH- = charge balanced HOH or H₂O —> e (photon).

[Fred Nerks]

http://www.popsci.com.au/space/riding-a-shrinking-comet-toward-the-sun,407858

is this page the source of your images?

[Candor7]

H2S is highest on the bar graph, and so it truly is a cosmic fart, with the right odoriferous gas component, aided by methane.