Our planet, for example, is a rocky planet, I know: It's mostly rock, even the middle, which is to say it's mostly solid, not liquid or gas. The gas part of our planet, the atmosphere, extends out only 300 miles, so calling our planet a gas planet would be wrong; if I were to consider the atmosphere part of the planet...
...which it seems to me you have to, if you're going to allow gas planets to be gas planets, because every planet astronomers call a gas planet is mostly or completely just atmosphere...
... if I consider the atmosphere part of the planet then ...
the Earth, which has a diameter of 7,926.41 miles is 8,226.41 miles counting the gases, and only 3% of our planet's total diameter is gases.
I got to thinking about this because of Mr Bunches' interest in the planets, which has rekindled my own interest in the planets. Mr Bunches recently got himself a book about the planets.
Actually, he got himself two books about the planets. He got the first book about the planets on a trip to the bookstore, and that book came with not just the book, but also a miniature orrery and a planetarium that runs on one AA battery and so it's not very bright and doesn't exactly light up the entire room with the stars the way one would hope a planetarium would. The night this little AA Planetarium worked the best was the night that we had a blackout that lasted 1 1/2 hours during a thunderstorm, and Mr Bunches was not in a mood to know that the planetarium worked because he was out-of-his-mind crazy with terror.
Mr Bunches does not like the dark. He doesn't even like the dim. He wants things bright, and when he goes to sleep at night it is in a room that is lit by a bright overhead lamp and his TV and, a recent addition, his nightlight. That is barely enough, and if we wait for him to fall asleep to turn off the light, he might sleep through that but if he wakes up he will holler until someone comes to turn on the light, at which point he'll drop right back to sleep.
Blackouts are terrifying occasions for Mr Bunches, because they only occur at night and because they leave him in absolute pitch black, as it did one Saturday night recently when it started raining and the boys were in bed, almost asleep. Sweetie and I were watching TV and the rain intensified until it got hard enough to knock down a power line somewhere, and all the lights and televisions went out.
It took less than 0.00001 seconds for an unearthly howl to emanate from Mr Bunches' room down the hall and by the time we got there, about 5 seconds into the blackout he was pounding on his door and sobbing. Sweetie had to hug him and calm him down while we tried to convince him it was okay, but he was having none of it; he kept crying and being scared, even after we went downstairs and used our laptop and iPad, both with batteries, to provide a little light. We tried to get him to sit and play some games on the computer to calm him down but it barely registered. He mostly sat on the couch, hugging Sweetie and crying and asking her if "they" could "just find the morning."
(Mr F was unaffected by the blackout, really. Mr F is unaffected by many things, being mostly easygoing and accepting of his lot in life. Mr F came downstairs and sat with us while we waited for the lights to come on. After a while, when they didn't, Mr F wanted to go back up to bed. I didn't feel right about him sitting in a pitch black room sleeping. It's one thing when a room is dark by choice -- the darkness isn't as bad when you can fling it away from you at a flick of a switch. It's another thing when it's there for good and you can't do anything about it, so I took an alarm clock that we had that has a button you can push to light up the face. I taped the button down and put it in Mr F's room with him, and gave him a little flashlight we had to hold. I sat there reading my Kindle while he slept, the flashlight unheeded near him.)
Eventually, Mr F was asleep and I saw Mr Bunches' planetarium and took it downstairs; I thought if he saw the stars on the ceiling it might calm him down, so I lit it up and looked, and because everything in the world was dark, the dim, AA stars were bright enough to make a soft, fuzzy universe on our kitchen ceiling.
I said to Sweetie "Have Mr Bunches come see" but by then he had drifted into a fitful sleep and eventually the lights came back on. It is sadly ironic that for Mr Bunches to make full use of one of his favorite toys he will have to suffer through an experience that is nightmarish for him.
(Mr Bunches had to get the second planet book, which was identical to the first, because Mr F accidentally broke the orrery that came with the first planet book, so we went and bought a replacement.)
In Mr Bunches' book of planets, the book talks about how Jupiter has a core of rock somewhere down inside it, confirming my suspicions that gas planets aren't always gas planets the way I think of them. Another book of Mr Bunches, one I bought him because he was getting bored with his first book of planets, says that one of the other gas planets, I think it's Neptune, is made up of frozen gases, which at first seemed to me to be cheating: if you're going to say it's a gas planet, then it can't be solid, right? Think about if Neptune really were made of just hydrogen and oxygen. If it's a gas planet, then it's nothing but air, right? And if that air is frozen, then it's simply an ice planet, not a gas planet: ice is the solid form of the gaseous state for water. Or something like that.
This all made me wonder why there are gas planets, and specifically how they work, so I spent some time yesterday reading about them and trying to figure it out: What would make the gases cling together as a planet, spinning and swirling? Why don't they just dissipate? Does our atmosphere dissipate? Maybe a little? Maybe some atoms escape from our gravity but mostly they're held by the mass below them, is how I understand it, but in a pure gas planet, then what would be the center of gravity that holds them together, I wondered.
It's not like I have the answers, because a day of paging around on the web doesn't replace years of studying astrophysics, but here is what I have gleaned so far:
Gas planets are stars that dropped out.
Jupiter, Saturn, those kinds of planets are collections of gases that never quite ignited as stars. They weren't big enough for nuclear reactions to start, or they were made up of the wrong elements to start burning (according to the book The Disappearing Spoon, which I'm reading, stars can only create elements via fusion up to iron before they explode, so all elements beyond iron were created by exploding stars and can't be used by normal stars.)
Jupiter, for example, is mostly hydrogen and helium, just like a regular star, but it's too small to spontaneously combust, so instead it starts it's own weird reaction, like having a molten core of gases that react like plasmas, but not quite, and by having an electrical-conducting outer metallic shell of hydrogen, which when I read it made me think that Jupiter is actually like this Giant Electric Metal Balloon of Wonder, orbiting the sun,
I also found out that gas giants isn't exactly accurate. The term comes from a science fiction writer: James Blish, who used it in a rewrite of his story Solar Plexus, back in the 1950s. Scientists are starting to use Jovian to describe gas giants that are more like Jupiter, while referring to Neptune and planets like it as ice planets...
...all of which got me to thinking about having been raised to believe there were gas giant planets and rocky planets, the dichotomy still used today in Mr Bunches' books of planets. What do we gain by dumbing down the universe in that way? When I was younger, I never used to question the idea that there could be a gas planet, but, then, when you are young you tend to believe a lot of things unless you are given a reason not to believe them.
For me now, it was Mr Bunches' little kids' book of planets that first told me that some of the gas planets were frozen and some had rock in them, and that caused me to think more, even, about those planets than I had in years, until I sat down and read more and learned just how weird our solar system really is. In a single afternoon I learned how big the Earth's atmosphere is, learned about how Jovian planets can give off more heat than they absorb, being something between planets and stars, learned about how ice planets and gas planets really behave, and was left with tons of questions to follow up on.
That's all well and good, but I'm forty-three. I may read and think about these things for a while, but what if, instead of being told that there were just gas and rock planets and that's it, move on, what if back in school I'd been told that Jupiter isn't so much a "gas planet" as it is a kind of star, almost, that's covered (we think) in a thin metallic electrical shield of metal, while its nearby neighbors are giant balls of frozen methane.
What if I'd been told that stuff, back then, and had started asking the questions at 10, 12, 15, that I'm asking now? Maybe I still would have become a lawyer, but maybe I wouldn't have, and there's be another physicist or astronomer out there.
I like to tell people about the astronomy class I took when I was in college, my senior year. I loved it so much that had I taken it freshman year, I might have majored in science. That professor did a remarkable job of making me think, ask questions, and he demonstrated in such a way how weird and awesome the universe is that I wanted to know more about science.
By that time, I was accepted in law school and committed to being a lawyer, and I've asked different questions as a result of the timing of those things.
All of which is to say: I probably should have woken up Mr Bunches, so he could see his stars that night.
UPDATE: RE: PT Dilloway's comment, below, and my Paul-Simon inspired response to it: