I thought I had published this article on solvent as the medium for life. I guess I was wrong. Today I was reminded of it by this article about some scientists who are trying to figure out what kind of life could evolve in liquid methane on Saturn’s moon Titan.
From the Eurekalert article:
“. . . many astronomers seek extraterrestrial life in what’s called the circumstellar habitable zone, the narrow band around the sun in which liquid water can exist. But what if cells weren’t based on water, but on methane, which has a much lower freezing point?”
“The azotosome (the material proposed for cellular life in liquid methane) is made from nitrogen, carbon and hydrogen molecules known to exist in the cryogenic seas of Titan, but shows the same stability and flexibility that Earth’s analogous liposome (the basis of our water based cells) does.”
And here’s my five year old article called “Solvent.”
On Earth the ultimate solvent is water. It lies on the planet in great swaths, covering almost three-quarters of it. But it doesn’t just lie there. It circulates around the continents in huge streams and mixes itself in small eddies. And it doesn’t just move horizontally. Water rises up into the atmosphere as a vapor and spreads out over the globe. In the air, water can take many forms. It can remain a vapor or it can condense out in tiny droplets or ice crystals, which can float in the atmosphere almost indefinitely. All the water will eventually complete the cycle many times over the eons, though. It will condense into drops or flakes or pellets and fall, some of it landing on the ground and finding its way back to the sea. While it’s doing all this it’s also acting as a solvent. Everywhere it goes it’s carrying all sorts of things that have dissolved in it. Water holds lots of interesting molecules that can engage in some creative acts of chemistry. And where there’s chemistry there are the raw materials for life. On Earth liquid water is the solvent that makes it possible.
The nagging question of whether there’s life on Mars hinges on the existence of water, preferably liquid, to support it. Were there Martian seas in the past? Is there water underground now? We know the planet has water thanks to the obvious polar ice caps, but we’re not sure if there’s enough to maintain a biological system. There’s encouragement in the fact that life exists on ice here on Earth. If Mars has plenty of permanent ice underground it might have a subterranean biosphere.
Farther out there are moons of Jupiter and Saturn that probably have global oceans under thick crusts of ice. Does any interesting chemistry happen there?
Also orbiting Saturn is a cloud-shrouded moon called Titan. It’s a large moon, about fifty percent bigger than our own, and bigger than the planet Mercury. Probes sent from Earth have studied it and found that it has plenty of useful molecules in its atmosphere and on its surface. It also has liquid methane oceans, lakes, rivers and rain. What kind of chemistry would go on there?
We’ve tacitly assumed that extraterrestrial life would be found, if at all, in the presence of water. Now some biologists are wondering if water’s required. Maybe some other solvent like liquid methane would do. While water is the ultimate solvent here, elsewhere it could be something else.