Looking back over the last few years of discoveries in our solar system has opened our eyes to the huge range of environmental conditions that could harbor life.
The uneven craters on the dwarf planet Ceres pose an interesting puzzle. Water ice was found on Mercury, of all places. I suppose finding volcanoes on Venus was no big surprise, but the ice mountains and fantastic geology on Pluto were awesome.
Oxygen was found on a comet by the Rosetta Mission. Earth-like planets with liquid water orbit around G-2 suns like ours. Such planets, like Kepler 452b, are very Earthlike with a diameter 1.6 times Earth’s and a 385 day orbit.
Then there is Enceladus, with its South pole geysers. Cassini has been orbiting it since 2004; it picked up carbon dioxide and salt from the geysers in October. This means the sub-ice lake, now thought to be an ocean that “…spans the globe,” is most likely very alkaline. This is good news, since most biological life on Earth likes soda water. More good news is that Saturn’s tug on Enceladus is thought to heat its under-ice sea to 90 degress C. near its rocky core.Temperature at the surface was –200 degrees.
Recently an isolated deep sea biosystem was found under very thick Antarctic ice. It makes one think of the subice oceans on Enceladus and Europa.
When looking for alien life, the role of minerals in rocks is not being ignored. Near hot vents, hydrogen, carbon dioxide and sulfur interact with rock mineral powder to create amino acids. Interactions occur on surfaces when water gets trapped between clay sheets.
On Earth, microbes in stromatolites could be as old as 3.8 million years. Oxygen in the minerals play a role. Early life here used minerals to build trilobyte shells in shallow oceans 500 million years ago and calcium carbonate shells even now.
However, chemical cocktails and liquid water may not be enough to kick-start life. The Cayman Unterborn at Ohio State University suggest that planets supporting life may need a “Goldilocks composition,” not just a nice warm zone in which to orbit. Tectonic plates, as we have here on Earth may be necessary.
When continental plates collide and dive under one another, this subduction helps keep carbon dioxide (for example from volcanic eruptions) under control, literally. Such plate tectonics comes to a screeching halt at 40 kilometers below ground (at least on Earth) unless
the proper chemical composition of the planet is able to make the diving plate more dense and sink deeper.
Therefore, in order to guess which exoplanets might host life, we should look at the chemical composition of their host suns, which should be quite similar. If the exoplanet is also orbiting in the Goldilocks liquid water zone, there is a far better chance for SETI to get an answer. If time doesn’t get in the way, of course. The life span of technological civilizations is another problem…