Kal-El, native of the planet Krypton, came to Earth and was adopted by Jonathan and Martha Kent. Being a Kryptonian, he found that he had superhuman powers and used them for good as Superman.
We all know the story. But what do we know about Krypton? Any information would be a dramatic coup for astronomers of all varieties. Superman couldn’t tell us, he was just an infant when he left. We might have to do some deduction. I propose we start by trying to determine the orbital period of Krypton – in other words, how long a Kryptonian year was.
To do this, we need the equation for orbital period. Without pausing for derivation, it’s:
What we don’t have is r, the orbital distance from Krypton to its sun (which happens to be named Rao), and M the mass of Rao. But I think we can estimate them. Rao is a red giant star, and those tend to put out a total amount of light that is much higher than the sun. Arcturus is a red giant of presumably similar classification, and has a total power output around 180 times that of the sun.
So clearly Krypton will have to be much farther away from Rao than the Earth is from the Sun, assuming the Kryptonian biosphere requires a similar level of heat and light as Earth’s life. This is a fairer assumption then it sounds: a depowered Superman is able to survive on the Earth on several occasions with no trouble at all.
Radiant intensity falls off as the distance squared. To reduce a power output of 180 times the sun to the same as the sun, you’ll have to increase your distance by a factor of the square root of 180. This happens to be about 13.4. That times the orbital radius of the earth is about 2 billion kilometers. This is a little farther than the orbit of Saturn.
So we’re half done. What’s the mass of Rao? Here we’re in sketchier territory. I assume it’s low mass by red giant standards to give it as long of a lifetime as possible given what we know in footnote 3. I’m going to give it half a solar mass, though red giants can exist as massive as around 6 solar masses. Bigger and they tend to be supergiants, another creature entirely. My 0.5 solar mass estimate has its problems but I think it’s about the closest we can get.
Plugging all that into the equation and I get a period of 69.1 years. It’s a very rough estimate based on shoddy information, and even if it’s accurate it doesn’t tell us all that much. But it might tell us some things. Life on earth is well adapted for the seasons which occur about once every 365 earth days. Assuming Krypton has an orbital tilt, how might life react to seasons which last for decades of earth time? It would be an interesting kink in the biology of Kryptonian life.
Maybe something a Daily Planet reporter might want to explore in the science pages. Especially if he happened to have some personal experience in the field…
1. A lot of people think Superman disguises himself as Clark Kent. It’s the other way around. Clark Kent psychologically thinks of himself as Clark, not Superman. Clark is who he is, Superman is what he does. (Batman is the opposite. Batman is who he is, Bruce Wayne is a convenient disguise.)
2. Depending on who’s writing the story, his spaceship may have contained a wealth of information. But we’ll assume we’re working on a version of the Superman mythos without this knowledge, or that it’s inaccessible to Earth scientists.
3. The Sandman: Endless Nights explicitly gives that classification for Rao, though the timeline seems sketchy. That story seems to happen around 3 billion years ago, and red giants burn fuel too quickly to continue existing until Krypton exploded 3 billion years later. Rao as a red dwarf seems more plausible, but I’ll defer to the story and assume I’m misinterpreting the timeline.
4. Some old comics also have Earth people visiting Krypton via time travel. The temperature and atmosphere seem to suit them fine, but Krypton’s gravity is stronger than earth and unprotected humans can’t tolerate it at all. Which, incidentally, probably puts the acceleration due to gravity at Krypton’s surface at about 5-20 times that of Earth, very roughly.
5. How is it that no other Kryptonian happened to be off of the planet when it exploded? It’s a long story.