But I am ahead of my story. This takes us into the engineering side of ecology. Ganymede was bare rock and ice before we came along, cold as could be, and no atmosphere to speak of—just traces of ammonia and methane. So the first thing to do was to give it an atmosphere men could breathe.
The material was there—ice. Apply enough power, bust up the water molecule into hydrogen and oxygen. The hydrogen goes up—naturally—and the oxygen sits on the surface where you can breathe it. That went on for more than fifty years.
Any idea how much power it takes to give a planet the size of Ganymede three pressure-pounds of oxygen all over its surface?
Three pressure-pounds per square inch means nine mass pounds, because Ganymede has only one third the surface gravitation of Earth. That means you have to start with nine pounds of ice for every square inch of Ganymede—and that ice is cold to start with, better than two hundred degrees below zero Fahrenheit
First you warm it to die freezing point, then you melt it, then you dissociate the water molecule into oxygen and hydrogen—not in the ordinary laboratory way by electrolysis, but by extreme heat in a mass converter. The result is three pressure pounds of oxygen and hydrogen mix for that square inch. It’s not an explosive mixture, because the hydrogen, being light, sits on top and the boundary layer is too near to being a vacuum to maintain burning.
But to carry out this breakdown takes power and plenty of it—65,000 Btus for each square inch of surface, or for each nine pounds of ice, whichever way you like it. That adds up; Ganymede may be a small planet but it has 135,000,000,000,000,000 square inches of surface. Multiply that by 65,000 Btus for each square inch, then convert British thermal units to ergs and you get:
92,500,000,000,000,000,000,000,000,000,000 ergs.
Ninety-two-and-a-half million billon quadrillion ergs! That figure is such a beauty that I wrote it down in my diary and showed it to George.
He wasn’t impressed. George said that all figures were the same size and nobody but a dimwit is impressed by strings of zeroes. He made me work out what the figure meant in terms of mass-energy, by the good old E = MC2 formula, since mass-energy converters were used to give Ganymede its atmosphere.
By Einstein’s law, one gram mass equals 9×1020 ergs, so that fancy long figure works out to be 1.03×1011 grams of energy, or 113,200 tons. It was ice, mostly, that they converted into energy, some of the same ice that was being turned into atmosphere—though probably some country rock crept in along with the ice. A mass converter will eat anything.
Let’s say it was all ice; that amounts to a cube of ice a hundred and sixty feet on an edge. That was a number I felt I could understand.
I showed my answer to George and he still was not impressed. He said I ought to be able to understand one figure just as easily as the other, that both meant the same thing, and both figures were the same size.
Don’t get the idea that Ganymede’s atmosphere was made from a cube of ice 160 feet on a side; that was just the mass which had to be converted to energy to turn the trick. The mass of ice which was changed to oxygen and hydrogen would, if converted back into ice, cover the entire planet more than twenty feet deep —like the ice cap that used to cover Greenland.
George says all that proves is that there was a lot of ice on Ganymede to start with and that if we hadn’t had mass converters we could never have colonized it. Sometimes I think engineers get so matter of fact that they miss a lot of the juice in life.
With three pressure-pounds of oxygen on Ganymede and the heat trap in place and the place warmed up so that blood wouldn’t freeze in your veins colonists could move in and move around without wearing space suits and without living in pressure chambers. The atmosphere project didn’t stop, however. In the first place, since Ganymede has a low escape speed, only 1.8 miles per second compared with Earth’s 7 m/s, the new atmosphere would gradually bleed off to outer space, especially the hydrogen, and would be lost— in a million years or so. In the second place, nitrogen was needed.