We know that Jupiter and Saturn are made mostly of helium and hydrogen, but is this true for other systems and their gas giants too?
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Depends on your definition. It seems Neptune-type planets are either included, or not included, varying from speaker to speaker. They’re mostly volatiles, as opposed to what we’d call “rock”, and do have H/He right at the surface. But, it’s largely ammonia and water underneath, instead.
Matter in the universe is 98% hydrogen and helium (as of the current billion years, anyway). Any strong enough gravitational field is going to end up pulling in a lot of it. Smaller fields like ours tend to have trouble holding on to it, because it doesn’t take much solar wind to blow it off. So, yes, any Jupiter-sized gas planet should have that composition. Although, there’s at least one known example of a former, or maybe potential, gas giant, that’s been stripped down to it’s core.
Public service announcement that when you vent helium into Earth’s atmosphere, it blows off into space forever, and we’ve used up a lot of the stuff already.
Most of the universe is hydrogen.
I don’t know if we can tell reliably (yet) what exoplanets are made of, but generally the assumption is that our solar system is chemically typical, so we extrapolate that for other star systems.
We actually can, from stellar transits!
Some of them are pretty weird. Molten silica clouds and rain come immediately to mind.
Most matter is hydrogen but then, supposedly, there is dark matter and dark energy 😯 !
There is a new model that I read about the other day that avoids the need for dark matter/energy and extends the age of the universe.
I’ve always (armchair astro physicist) thought that the dark matter/energy was always just a fudge to fit an ill-fitting model to observations (which isn’t inherently wrong). It just means the model is wrong.
i like that as well
Mostly, just because almost all matter in the universe is those two elements. However not always true. Uranus does have a very thick hydrogen and helium mixture in its atmosphere (80%/15%), but it also has a solid core, and technically by mass is mostly water, ammonia, and methane in a supercritical ice phase.
It’s bonkers how the universe is almost entirely H and He and yet, here we are.
Poetically it’s been said that we are stardust, or star stuff. More grounded, we’re the extremely minor byproducts of a star’s explosion.
Carl Sagan famously said that from his 1980 television series “Cosmos”:
“The Cosmos is within us. We are made of star-stuff. We are a way for the Universe to know itself.”
What I didn’t realize at the time was, he probably made up that word to avoid using the word “stardust” that Joni Mitchell used in her song at Woodstock, which certainly had some influence on him.
If we want to get kind of nitpicky, water, ammonia, and methane are also mostly hydrogen
If we really get nitpicky, all the atoms in all of the elements are mostly made of empty space, aka nothing.
The whole universe is mostly nothing, just like the stars and plates too.
If we want to
keep the thread goingget even more nitpicky, empty space doesn’t exist, exacly. There’s just one big quantum field filling the universe.Although, future physics may change that picture.
Uranus is made of methane.
