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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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.
Joni Mitchell wasn’t at Woodstock. The song was named Woodstock.
If we want to get kind of nitpicky, water, ammonia, and methane are also mostly hydrogen
No, by mass, they’re certainly not.
If we really get nitpicky, all the atoms in all of the elements are mostly made of empty space, aka nothing.
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.
The whole universe is mostly nothing, just like the stars and plates too.
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.
Depends on your definition. It seems Neptune-type planets are either included, or not included, varying from speaker to speaker.
I’ve also heard them referred to as “ice giants”. Are they a subcategory of gas giants, or separate category?
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.
That’s not really true though. There are multiple lines of evidence. We can calculate the mass, we see the effects through gravitational lensing, there’s the CMB evidence etc. And we can’t forget the bullet cluster, which has a different distribution of dark matter, showing that most theories that make some global changes to physics such as MOND cannot be true.
This is way more than fudge factor. Everything is consistent with a something that doesn’t interact except through gravity.
As for dark energy, this very question was covered in a podcast that you might be interested in listening to. https://www.iheart.com/podcast/105-daniel-and-kellys-extraord-29862087/episode/is-dark-energy-a-fudge-factor-343402032/
That evidence is not evidence of dark matter (that’s the problem), it’s evidence that we’ve modeled gravity or spacetime or inertia or whatever wrong.
It’s like drawing triangles on spheres or other non euclidean spaces, but for mass/inertia. Maybe the problem with the Hubble constant is the clue.
If you need a big fat invisible undetectable magic amount of mass or energy to make it all work, perhaps some of the underlying assumptions are incorrect.
It might be a big fat invisible undetectable magic amount of mass or energy, but it’s not the only option. It is an inelegant option.
How can any change to gravity globally accurately describe the bullet cluster? I’ve never seen a MOND theory even try to do that. They keep talking about galaxy rotation and forget all the other lines of evidence.
There appears to be quite some debate between several competing theories.
Apparently MOND can explain that cluster with ‘only’ additional cold hydrogen.
i like that as well
Uranus is made of methane.
Got a couple of anti-science dorks here.
