I admit it---I am fond of the icy worlds, and there are a lot of them out there, especially beyond the galactic halo. The Milky Way itself is unusually hot and dense, and then once you go out the clouds at the rim, you get those little red dwarf stars with their little icy planets, silicon and aluminum and just a little bit of iron, no plate tectonics, orbiting in their shadows. When I walk out there, I can feel almost like I am on some little corner of earth. That is what Baker did, when he would walk out to the Sagittarius Dwarf Galaxy and made a catalog of all the places he would sit down. No real body, so the cold doesn't bother us. We can't breathe, either, of course, but for some reason we all feel better somewhere where there is an atmosphere, even if we can't breathe it.
And Baker 246d fits those criterion, but it has something special. It is the planet that is alive, and dies all at once, and then comes back. The crust and surface of Baker 246d is light rocky elements--- lots of silicon, magnesium, a little aluminum, slight amounts of iron and calcium. Lots of oyxgen. Silicon dioxide, basically. Glass. An entire planet of glass, but it is living glass. The atmosphere is methane, ethane, carbon dioxide, of course, and what happens is that the surface starts rusting, or else it starts growing. Some metabolic process starts catalyzing all that silicon dioxide in the crust and all that carbon dioxide in the atmosphere, and all those hydrocarbons and magnesium and everything else to start turning into...well, it is a lichen. Made of glass. Big sheets and crystals and flakes and layers, big involuted and convoluted "leaves" start sprouting up from the surface. But two things about this: there are no cells or individual organisms, it is like the entire surface of the planet billows out, forming layers that really do look like lichen, except they can be dozens of feet high. Oh, and it happens very slowly. Cool red sun, icy planet. The metabolization takes a long time---maybe millions of years. There are no "predators", there is nothing that breaks down the complicated carbon-silicon bonds of these living crystals. They only have one enemy.
The silicon dioxide and carbon dioxide combine together, releasing oxygen. Slowly. It builds up in the atmosphere over more than a million years. Some people, including old Baker himself, say it takes an entire circuit of the galaxy through the Milky Way, and for good reason. Because even as the oxygen reaches a high point in the atmosphere, it is too cold for combustion. It just builds and builds. And then when the entire system gets close to the galactic plane, there is a chance of a meteor entering the atmosphere--- burning through, thousands of Kelvin on a planet that is usually just above the melting point of ethane. And a fireball goes through, the oxygen recombines with all that silicon and carbon, and the entire planet, millions of years of delicate leaves of lichen growing over that frozen surface---burns up in a few hours. I haven't seen it. But I can believe it. The leaves of lichen are pretty thick...I come here and sit down, counting my (non-existent) breaths while looking over that forest, those rolls and involucions, those layers and turns and gill like structures, slowly spreading outward...and I think of it all falling to ashes in a relative instant, and then the whole thing regrowing back in the relative peace of the galactic poles.
It really puts things in perspective, doesn't it? All that icy, calm, blue and white strillations underneath me, that look so calm and peaceful---even that isn't forever. Something to think about, before I have to head back to earth. Because while the calm crystal clear nights of a low density, low drama planet orbiting slowly around a little red dwarf way outside of the main bars and whirls of the galaxy might think like a place to escape...they have their problems too. But ones I can ignore for another hour or month on an astral walk as I see what life can be, uninterrupted.