Why shouldn't it separate from heavier gases and rise like water vapor — or does it? (realclimate.org)
The sound track is scintillating enough at idle and small throttle openings, but valves open up the system with heavier gas pedal applications to a rumble complete with lusty crackles and pops. (nydailynews.com)
«This will allow us to search for heavier gases such as carbon, methane, water, and oxygen, which could offer biosignatures for life.» (planetaria.ca)