EDIT:
On speculation about hypothetical biochemistries:
Eagle1Division, I've looked at alternate biochemistries as well. And the trend I keep saying is people saying "Ooh, this sort of chemical environment could exist here, this solvent or this chemical or whatever could do X, X and X". And then other people come along and point out "But this chemical environment has Y problems, and this solvent or whatever has A, B and C disadvantages".
I'm not asking for an end-all design for an alternate biochemistry. I'm asking for a single design. Any design. Any vague description of how such a biochemistry could work, along with in-depth simulations or studies. I haven't seen that anywhere yet. It's all just stuff like "ooh, but this could happen with this and this, you could have a halogen-based world, or a planet at 200 degrees C", or whatever. There's no actual detailing behind how these organisms could work.
And if you look at the alternative, you'll see that it's essential to come up with models for how such life could work, because if we don't, we're basically just assuming stuff. I'm not saying that "X theoretical biochemistry" would predominate on a planet like Titan, or even whether it
would exist at all, but if we don't run studies, an actual study that deals with the actual chemicals interacting in the actual environment, we can't assume that something of the vague flavour would work, or
how it would work.
I'm not even saying that alternate biochemistries are impossible. I am saying that they likely face several challenges and problems in the face of becoming
complex or advanced life. From what we know about chemistry- it
is about chemistry, that there are several reasons why some of the "alternate" biochemistries described would face disadvantages.
On life-speed at cryogenic temperatures:
What I was trying to say is that at lower temperatures, molecules move at reduced velocities. I am not talking about the energy that reactions yield
at all. I'm not talking about rust, or rocket engines. I'm talking about how fast stuff can interact at the micro and nano-scale. DNA replication, for example, or its equivalent. The rate at which that sort of stuff happens dictates a whole lot of other things.
On movement of plants and animals:
Plants don't move fast because they don't need to. Yes, heterotrophs move faster because they survive on energy that has already been concentrated. But they also have to go out and get that energy; they don't sit around in the sun all day effectively getting it for free.
You
don't have to be a carnivorous plant to have rapid motion. And some sessile animals (in this case, heterotrophs) movequite quickly
barnacles feeding (barnacles are, believe it or not,
crusteceans).
It isn't an argument for fast moving supercold biochemistries. It's just an argument about how different organisms adapt differently to different lifestyles. It doesn't have anything to do with the results of reduced interaction rate.
The difference between autotrophs and heterotrophs is quite obvious on land, but in the oceans it's different; a lot of the time, niches held by "plants" are in fact held by animals, which may or may not be in symbiosis with autotrophs. The uneducated person might regard a sponge or a coral or an anemone for a plant, but they're not.
There are plenty of organisms in the ocean that are sessile or slow moving and do quite well as heterotrophs.
Here's a pretty interesting video of a landscape of slow-moving organisms, in quite an alien environment (warning; gets gory at ~1:22).
Life - Timelapse of swarming monster worms and sea stars
Reef Aquarium Time lapse of Star polyps
There could be various reasons why life could evolve in such a way. It could have to do with senses. Or movement organs. Or nervous system evolution. Or extinction rates. Or just plain luck. Just because you're a heterotroph doesn't mean you have to move at speed X or speed Y. Heck, on an alien planet one need not assume that something like a heterotroph or an autotroph would even be that distinct. On Earth they're quite distinct on land, but somewhat less so in the water- there it's common to find organisms in symbiotic relationships. And lichens, after all, are symbiotic organisms-
Saying that something can't exist without problems on even a small amount of evidence is one thing, saying something can exist and act in a certain way without adequately illustrating possibilities is another.