In contrast to Earth, Mars's middle atmosphere appears driven by gravity waves | Hacker News Reader

In contrast to Earth, Mars's middle atmosphere appears driven by gravity waves

phys.org

74 pointswglb32 comments

Referenced article: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023JE00...

> Not to be confused with gravitational waves from massive stellar bodies, [gravity waves] are an atmospheric phenomenon when a packet of air rises and falls due to variations in buoyancy.

For those similarly confused by the title as I.

I used to thing programmers were bad a naming things until I became interested in physics.

Related to this discussion, astronomers’ usage of ‘metal’ is a fun example.

And musicians!

Salts in chemistry too

"it can't be that bad, can it?"

> astronomers use the word metals as convenient shorthand for all elements except hydrogen and helium

what, ok

Yeah, fun, right?

I've looked up why before, tldr it's just because historically astronomers have never had to care in any detail about chemical reactions (this is not strictly true of course, but somewhat close for at least a large subset). So they just need a term for "crap that came from stars".

Eh, that grosses over the defining difference that hydrogen, helium, and a little bit of lithium are everywhere everywhen all at once because of The Bog Bang, whereas everything else is concentrated due to being produced in supernovas and neutron stars.

Reminds me of: https://xkcd.com/2205/

Isn't there predicted to be liquid metallic hydrogen in Jupiter's core?

Metallic as an adjective, behaving like a metal - due to the insane pressures. Different usage of the word "metal".

So for astronomers, metallic means "behaving like everything else other than hydrogen and helium".

In fact, I'm guessing "metal" (noun) came from use of "metallic" (adjective). The mention of helium betrays it - helium is what hydrogen behaves like normally "due to the insane pressures" (and heat), so what it basically says is just "not hydrogen".

"Metal" to astronomers simply means "non-primordial". As in, not created by the primordial nucleosynthesis.

To keep on topic, that makes Earth's and Mars' atmospheres consist of metals.

Hydrogen can be a metal too. https://en.wikipedia.org/wiki/Metallic_hydrogen

Point is, not in the astrophycisists’ use of the word (and not really in any other use either – metallic hydrogen is not a metal, just behaves in some aspects like metal). To astrophysicists, hydrogen is not a metal by definition, which is literally "everything except hydrogen and helium". No matter how exotic a phase.

Nb. The subset of astronomers who call everything after helium "metals" is mostly disjoint from the subset that’s interested in gas giant interiors.

Wait until you spend time learning probability, or worse, biology.

Worse than math, where set theory, type theory, group theory, and category theory all exist and refer to barely-related things?

I really can't see why they are called categories... Do we have anything that we categorize and get categories from it? Looks like another synonym to "set" and "group" that wasn't used so far.

So in a thread about Mars's atmosphere, we wind up at category theory.

Never change, HN, never change.

Reminds me of that article[0] that says the trebuchet is a gravity weapon. That's because it's the gravity that does both the launching and the dropping.

With some interesting consequences that sort of justify calling it that.

[0] - https://michaeldominik.substack.com/p/physics-rediscovered-i...

I am cynical but, I am pretty sure the ambiguity was intentional

Seriously, what a dumb title. Anybody who knows what gravity waves are is gonna read it and go “what?? no.”

You are confusing gravity waves and gravitational waves.

Gravity waves are waves where the restoring force on some medium comes from gravity. Waves you see on the surface of water, for example, are gravity waves.

Ok, that’s a good point. But gravity wave is commonly used as shorthand for gravitational wave.

But not in this case, so your criticism was unwarranted.

No. It's your criticism that is unwarranted.

You're totally onboard with the scurrilous "dumb title" slur?

Yeah I love slurs

One type of gravity waves can be seen on Earth where its atmosphere meets large bodies of water. These are commonly known as ocean waves.

As always - relevant XKCD - https://xkcd.com/2340/

Reply on news.ycombinator.com