While I was perusing some Wikimedia Commons images to find an illustration for an article, I stumbled across this gorgeous concept image, created by Wikimedia user lttiz. This is an impressively well thought out depiction of a world dominated by life with a biochemistry based around ammonia instead of water like here on Earth.
Lttiz continues to give a rationale for the appearance of this image…
“The ammonia oceans, if it were just ammonia, would probably appear blue just like water. However unlike water ammonia can dissolve alkaline earth metals as if they were salt. When this happens the color changes. Dilute amounts of metal give it a an intense blue color, slightly higher concentrations give it a gold bronze color as shown here.”
I remember an undergrad chemistry lecture all about this actually. Interestingly enough, not only does a solution like this have a metallic colour, but it’s also a good conductor of electricity. Even better than saltwater, in fact.
“The reddish orange color in the atmosphere is due to oxides of nitrogen (nitrogen analogs for oxygen). Like Earth the atmosphere is primarily diatomic nitrogen. Unlike earth it contains next to no free oxygen, but has nitrogen oxidizers. Most probably nitrous oxide, but it could be nitric oxide. It’s hard for me to figure out which would be more likely.”
It’s hard to say which gas would be more likely, to be honest. Mind you, nitrous oxide (laughing gas) is actually colourless, and so is nitric oxide (decidedly less humourous gas). Nitrogen dioxide, however, is a reddish brown colour.
“The planet would be much colder than Earth so I depicted the vegetation as black to collect more light. Unlike water worlds like Earth, plants on ammonia worlds may not need to deprotonate water (or ammonia) molecules to get an electron for photosynthesis. This is because the dissolved alkaline earth metals release solvated electrons which can be used directly. This could free up photosynthetic plants to use a wider range of the spectrum.”
This part I like rather a lot. Ammonia would need a lower average planetary surface temperature to be liquid. Lower temperature means less insolation from the planet’s host star, so plant analogs would need to have darker pigments to be more efficient. Which makes perfect sense. This would be a dark world to live on. That said, with less visible light, anything which evolved to live here would probably see in infrared.
“Finally ammonia clouds and ice are white just like water.”
Because of the way light gets scattered, most ices and vapours which don’t absorb optical light strongly would appear more or less white like this.
Of course, there’s no way to prove any of this to be true, but it certainly seems quite logical to me. I can’t help but wonder if a planet like this really does exist somewhere out there in our galaxy…