Eli5 why is Jupiter surface is gas if it’s so far from the Sun?
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How are those two things related? Do you mean because it’s relatively cold way out there? You’re right it is cold, but Jupiter is made of mostly hydrogen and helium, which are a gas all the way down to within a couple degrees of absolute zero. That’s why Jupiter is a gas planet, it’s made of materials that are well above their boiling point even way out in space where it’s relatively cold.
Our solar system was once a massive cloud of dust and gas called a “nebula”. Slowly the gas and dust started to collide and collected. In the center it collected enough gas that the gravity from all that gas began to press it together. Eventually the pressure was enough that the gas began to undergo fusion which released light and heat. However that didn’t happen everywhere. The outermost planets formed from much less gas. So there wasn’t anywhere near enough gravity pulling it all in and starting a fusion reaction.
Actually they’re related, and relate to another neat thing about the solar system!
So the lightest element is hydrogen. It’s used in stars for fusion, it makes up the bulk of gas giants, and is a crucial part of life on Earth by being part of water.
However if you get enough of anything, it’ll pull itself together because of gravity.
If you get a bunch of hydrogen together enough to make a ball, you get a gas giant. If you get even more, you get a star, because there’s so much there that it’s being pressed into each other to turn the hydrogen into helium.
Stars are a balancing act though. There’s so much mass that they want to collapse into a little ball, but the fusion in the center prevents that because it’s so much energy.
That energy leaves the star with enough force to shed little particles all around the star, this is called “solar wind”
Solar wind happened the moment that the sun began fusing though and that pushed all of the lighter elements, like hydrogen out of the inner solar system. However, there’s a point (around Jupiter, it turns out) that the solar wind doesn’t have enough force to push it out of that area.
After millions of years, each planet controlled all of the rock, dust, and gas in their orbits, and they’re mostly stable today.
“But what’s the other neat thing?” Well, you know how I said it pushed all of the hydrogen out of the inner solar system? That included all of the hydrogen that Earth has for water. So in the process after fusion has started, but before our modern stability, we collected so many asteroids and comets (it’s thought to mostly a special type of asteroid called a [carbonaceous chondrite](https://en.m.wikipedia.org/wiki/Carbonaceous_chondrite) that we got our oceans that way!
~~Jupiter is a failed star.~~ It generates and emits vast amounts of heat energy from the pressures of helium and hydrogen collected by its enormous gravity. It’s not exactly “cold” there. In fact, if you dove deep enough into its atmosphere you’d find a layer where the ambient temperature would be comfortable for an Earthling, although the pressures at that depth would certainly crush you without a significant (impossible?) pressure vessel.
Simple: because the material it’s made of isn’t cold enough to be a liquid or solid. Hydrogen is very difficult to freeze, so even the cold temps out there aren’t enough to stop it from being a gas.
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