Breathable atmosphere

Question

The idea I have is an atmosphere with heavy gasses so the creatures that inhabit this planet have an easier time flying.

The temperature is colder than Earth's minimum of -119°, average of 12° and maximum of 37° Celsius on the surface.

The gases I have in my mind for this atmosphere are:

• 3%-5% sulfur hexafluoride

• 2%-5% argon

• 0,087% krypton

• 10% trioxygen (between 15-25 kilometers above sea level)

• 0,013% carbon dioxide (three times lower than on Earth)

• 25% oxygen
  All my creatures lack senescence due to a fast regenerating layer that protects genetic codes like RNA, DNA, TNA, PNA, GNA and XNA, so oxidation won't be a problem, but I wonder if the world would be too flammable.

• 60% Nitrogen

Can this support multi-cellular life capable of running, swimming, flying and gliding?

Can I somehow make flying even easier without decreasing the quality of life?

Answer 1

Can this support multi-cellular life capable to run, swim, fly and glide ?

Probably not. On the one hand, your SF6 concentration, about 100 times that of CO2 on Earth, implies a truly fabulous greenhouse effect, since SF6 is about 30,000 times more potent as a greenhouse effect than CO2. This suggests that the planet is far away from the star which it orbits.

At the same time, 10% ozone is an astounding level. In the Earth's Ozone Layer, the concentration is on the order of 2 to 8 ppm. So apparently the UV levels are enormously greater than at the earth, at the same time that the visible and IR levels are much lower. This in turn suggests that the "sun" for this planet is something like a neutron star and the emission of that class peaks in the x-ray portion of the spectrum.

Answer 2

This gas mixture doesn't seem to make flight significantly easier; its density isn't that high. A truly radical approach to this idea was invented by David E H Jones in 1967, who proposed xenon at 50 atmospheres pressure with 0.5% O2 as a breathable gas mixture with density equal to water. Unfortunately for this scheme xenon is a powerful anaesthetic, but sulphur hexafluoride is, apparently, safe to breathe.

So what you need to make flying easy is an atmosphere that's mostly SF6, with a little O2, at very high pressure. It seems very unlikely that such an atmosphere could happen naturally, but an advanced alien species might find it amusing.

Jones: The Inventions of Daedalus: A Compendium of Plausible Schemes, W H Freeman & Co, 1982. It's a collection of joke science columns from New Scientist magazine. Most of the ideas have a hole somewhere, but a few have been the subject of patent lawsuits.