I’ve been slowly collecting notes on the science that science fiction writers get wrong. I have this idea of using them for the basis of a high school level science class. In fairness, I don’t count things like the swamps of Venus or the notion that Mercury’s dark side never faced the sun and was perhaps colder than Pluto. I intend to focus on things that were known at the time a story was written. For example, the notion that gravity would hold structures and an atmosphere against the inside surface of a Dyson sphere.
One thing that crops up from time to time in science fiction stories is helium-II on very cold planets. Pluto is one target. Or imagine a planet that’s tide-locked with its sun, with the dark side near absolute zero. You could imagine streams of superfluid helium flowing uphill because that’s what superfluids do.
Well, it occurred to me to look up the temperature at which liquid helium transitions to superfluid helium-II. This temperature, the so-called lambda point, is 2.1768K, or 2.1768 Celsius degrees above absolute zero.
The cosmic microwave background corresponds to a temperature of 2.7255K, or nearly half a degree above the lambda point for liquid helium. That means a body floating in interstellar space will exchange heat with the surrounding sky by radiation until its temperature is equal to the microwave background temperature. As a result, the planet will remain too hot for superfluid liquid helium to exist.
So good-by superfluid helium based life forms.
Since then, I’ve read that the temperature can be lower inside dust clouds, where the energy from the microwave background hasn’t had time to penetrate into its depths. And that could be the basis for an interesting story.
It’s too darn hot.
It’s too darn hot.
I’d like to go superfluid tonight,
And flow against gravitation tonight,
I’d like to be superfluid tonight,
And flow uphill over walls in the night,
But I ain’t down to transition tonight,
‘Cause it’s too darn hot