Looking For Extraterrestrial Life In All The Right Places.
Ocean planets are an old idea in SF, but relatively new in the burgeoning field of observational exoplanetology. As the masses of discovered exoplanets goes down, the planets themselves are becoming less like gas-giants and ice-giants and more like bigger, wetter versions of Earth. Scott Gaudi, and colleagues, have studied just what the new “Ocean Planets” are like, with some interesting results.
In this abstract, like the news piece linked above, the interesting finding is just how far out an open liquid ocean can be maintained. If I’m reading the figures correctly, then between 3-5 AU (Asteroid Belt to Jupiter’s orbit) an ocean can persist under the right mix of a hydrogen/helium/methane atmosphere. That’s quite impressive, with all sorts of interesting implications for aqueous life, but not as we know it.
An AGU abstract list expands a bit further… Ocean-bearing planets near the ice line: How far does the water’s edge go? …session P13C-1333 specifically. It discusses denser atmospheres which won’t have liquid oceans – they’d be too hot past ~200 bar because of the efficient retention of internal heat.
Another AGU paper (here) finds that salt, specifically NaCl, will change the melting curves of Ice VI and Ice VII, high pressure polymorphs expected in the icy mantles of large moons and ocean planets. Planets with large water fractions (10-50%) will have large high-pressure Ice mantles, but – as all chemistry students know – the properties of solvents change in the presence of solutes. Salt in water/ice means it will remain liquid at lower temperatures, even under high pressures. With other solutes thrown in, there might be all sorts of weird convection and the like keeping the “ice” from being a static monolithic mass. That’s good news for life on all Ocean Planets.
Especially since statistical analysis of the exoplanets found so far indicates ~30% of Sun-like stars will have “Super-Earths” – likely Ocean Planets… (from here)
What is the frequency of Neptune or rocky planets orbiting
G and K dwarfs? A first estimate based on the HARPS
high-precision survey suggests a frequency of 30 +/- 10% in the
narrow range of periods shorter than 50 days.
Will they be habitable? With such short periods, they’ll be hot around G stars, but late K stars are getting kind of dim. And the HARPS data for planets a bit further out might reveal even more planets in the right place…