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Comment by kaycebasques | Hacker News Reader

The ingenuity (and accumulated knowledge) of people never stops amazing me. "Well, we can't actually drill into Mars to see what it's made of, so let's slap a marsquake detector on the surface and we'll measure seismic energy from meteor impacts to figure out what this bad boy's guts are made of." Of course no NASA person actually talks like this; I have been reading too much Heinlein.

Also, they use the term "marsquake". Never stopped to think about how geocentric the term "earthquake" is!

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As the article shortly touches on, it's how we know what the earth is made out of too. Our deepest borehole reaches 0.2% of the distance to the middle of the earth, most of what we know is instead from measuring seismic waves from earthquakes.

My question is, if we were to dig a hole to the centre and carve out a sphere there, would the very central point have no gravity?

My thinking is that the mass is in all directions so the gravity would cancel out in the middle. You’d then have an inside surface you could run around on which would have gravity.

Yes! In fact, as you go down the borehole, gravity will decrease linearly, until it reaches zero at the center. Strictly speaking, not quite linearly, since the earth’s density is not uniform. Thinking of the earth as made up of concentric shells, it turns out that once you’re inside a spherical shell of uniform density, that shell contributes zero to the gravitational field. Outside of it, OTOH, the shell produces gravity as if all its mass were located at the center.

One of my favorite fun facts is that if you were to dig a frictionless borehole to the other side of the world, you could hope in, be accelerated towards the center of the earth, decelerate on your way up to the other side, and pop out with 0 velocity 42 minutes later.

Now, this is the fun part, the 42 minute time frame is true for using gravity to coast through a straight hole between any two locations on Earth's surface!

(Assuming a perfectly uniform density sphere and no friction on your journey of course)

It’s fun to think about, but frictionless means you’d have to pump out the air. So you’d need to wear a space suit, and heat shielding. It’s kinda hot down there.

"... For here, at the very center of this watery globe, there seemed to be no gravity. There was collossal pressure, certainly, pressing in from every side, but one was in effect weightless ..."

In French "to land" is "atterrir" (to earth). So we have "alunir".

>The eagle has mooned !

https://en.wiktionary.org/wiki/amarsir

“earth” (with a lowercase letter) means roughly the same thing as ground, land, soil, etc, just like “terre” in French.

'right' and 'droît' work the same way too. Right as in direction, right as in ethics, and right as in civics.

I love this in so many ways!

Wait there is more, a water landing is https://fr.wikipedia.org/wiki/Amerrissage (mer = sea)

On Titan, this could be called an améthanissage (for methane).

moonquake exist too ! https://edition.cnn.com/2023/09/14/world/moonquakes-apollo-1...

Some people call Hacker News the "Orange Site", but of course that's way too fruit-centric, so we shouldn't call it that -- the website banner is not actually a citrus fruit at all!

Or can we just accept that orange-the-color is a fundamentally different idea than orange-the-fruit, despite the fact that the former is named after the latter? Can we accept that "earth" can simply refer to the material that makes up the hard surface layer of a planet, as a different idea than "Earth" the planet after which it's named? Is that OK? Do we really need to come up with a new word for "Solar Power" if the power comes from a light source other than our own sun? Can we call the large-scale geoengineering of Mars "terraforming", or must we insist that it's "marsaforming" (and not "geoengineering", but "marsoengineering")? Can we call something "romantic" even if it isn't actually written in Latin ("from Medieval Latin rōmānicē, Vulgar Latin rōmānicē (“in the Roman language”, adverb"))? Is that OK with everyone?

It's a damn earthquake.

..how did the words 'marsquake' and 'geocentric' set you off so badly? None of your examples even loosely fit the mold, 'terra' and 'geo' don't refer to a specific planet in this context at all.

Marsquake is a fun word. You can also call it an earthquake and no one will bat an eye.

I'm not sure why I agree with the op, but I do. I think it has something to do with the fact that this convention of planet prefix, and geological activity suffix is not going to work well at astronomical scales. Epsilon-eridani-c-quake is kind of a mouthful, no?

It could be argued that doesn't work very well on a human scale either. after all when there's an earthquake, barring a civilization-ending apocalyptic situation, it's not the whole Earth that's quaking (at a human scale perspective), but rather a localized crustal region of it. A patch of earth (lowercase).

This is akin to worrying that the sky is falling when literally two drops of rain fell.

"Oh my god, what are we going to do when the rest of it comes?!"

Cute nicknames don't scale and thats OK. Worry about it when scaling becomes a problem.

> 'terra' and 'geo' don't refer to a specific planet in this context at all

Although originating as basically meaning "dry land", the word "Terra" became a proper name for the Earth in Latin around the Renaissance. The prefix "Geo" comes from the Greek for "Earth", the name of our planet. If you argue that "geo" really just means "land, ground, soil", etc., then you are exactly agreeing with me, since the word "earth" went through the same evolution: Geo-the-planet was named after geo-the-dirt. Earth-the-planet was named after earth-the-dirt.

If we start retiring Earth-centric terms too quickly, we'll have to invent tons of planet-specific cognates: not geography but marsography, lunagraphy, etc. Same with Sun-centric terms vs other star systems.

I would suggest going for generic terms like "planetquake".

Selenology and selenography are both already in use.

I specifically said in this context because I had this certainty you would form an argument from the origins of the word.

My whole point is that "earthquake" refers to the material called "earth", meaning "dirt", or "soil", or "the material making up the top layer of a planet", and that we should stop making up new words for everything that remotely shares an origin with the word for the name of our planet. This is my entire point. We should not be beholden to the origins of the word (and even if we were, we still don't need to rename earthquakes that happen on Mars).

So you say: "geo-" and "terra-" don't refer to a specific planet in this context and I agree with you. That's the point. Neither does "earth-" in "earthquake". Are you trying to make the argument that "earth-" in "earthquake" refers to the planet Earth (rather than the material), unlike "terra-" and "geo-", or are you just completely agreeing with me on everything? I'm having trouble telling which is which.

Lets reset then and try to get to the root issue; your characterization of this as someone insisting is a total buzzkill, do you have to treat this like a bizzare moral pronouncement that you must denounce? If you can be chill about marsquake then I'll swear by all the fruit you can name to defend the use of 'earthquake' as correct regardless of the planet being discussed.

Personally, I'm a big proponent that the proper name for this planet is "Terra" not "Earth". So this whole discussion sets me off! ^_-

I'm quite fond "areoforming," actually. And "aerography," etc. From Ares, the Greek god who the Romans called Mars--I've seen it used here and there.

It's very much the same thing as "a gaggle of geese" or "a murder of crows." It's just a bit of fun. Nothing to get worked up about.

That raises an interesting question, is the surface of Mars made out of mars, or is it made out of Earth? In english, capitalizing a noun clarifies this, but that approach may not generalize to other languages.

Once we start construction on mars, will the machines be called marsmoving equipment?

Quake is sufficient, no need to apply designations.

Many things may quake, friends.

Indeed. Such as planets, love handles during aerobics, and Jello.

...or Quake 2

or even 3

and bowels.

Yes... and? Do you think that's problematic here? Why?

Language is pretty robust and we're able to deduce a ton of meaning from context. The term by itself is already used to refer to earthquakes. For all the other things that quake, we don't need to prefix them with the quaking entity to understand the meaning. You aren't going to say that someone was humanquaking in their boots so that people understand that the person wasn't actually experiencing anything on the Richter scale. Similarly, if I mention a quake on Mars, it's pretty apparent I'm not referring to Mars trembling in fear.

Yes, context can provide what an abstract term cannot.

As a suggestion, using the term "seismic" to refer to subsurface vibrations would be more specific than "quake."

Aye, kenning is a well understood linguistic principle, hence why quake is sufficient in English.

Once Mars is settled/colonized/freedom I'm sure political ambivalence will encourage people to rename earthquakes to marsquakes.

An earthquake on Mars very quickly becomes the local Martian government's problem when it is insanely expensive to fix.. and the vocab would follow..

> Can we accept that "earth" can simply refer to the material that makes up the hard surface layer of a planet, as a different idea than "Earth" the planet after which it's named? Is that OK?

No, the planet is named after the substance, not the other way around.

Of course I agree with you, which only strengthens my argument. But anyone who thinks we need to make up words like "Marsquake" clearly disagrees with you, and those are the people I am arguing against. It was a preemptive concession to ignore that point -- even if earth-the-material were named after Earth-the-planet, there's still no need to abandon the thousands of earth-related words as soon as we step foot on another planet. I felt that if I argued "Planet is named after material, therefore it's an earthquake" people would have missed the more important argument. (Not that any of this is particularly important.)

Is this a bit? It feels like a bit.

Not a bit, but maybe sport? I truly believe everything I said, and I believe it's a solid argument against a practice I see as silly and unsustainable: replacing any word that sounds superficially related to the name "Earth" as soon as the events are happening on some other planet. I'm saying that whatever reasons you use to avoid "earthquake" because it's on Mars, the exact same reasons mean you should avoid the term "romantic" to describe something that isn't written in Latin -- this shows the reasoning is deeply flawed. Basically a proof by contradiction. I hope that came across?

But of course I realize it's completely unimportant. Arguing is fun. It's not trolling: I'm not trying to get a rise out of people. Nor is it a bit: I'm not kidding or falsely representing any of my beliefs. I'm just having a bit of sport arguing with strangers online. If you see someone online making passionate arguments about minor word-use issues, or which superhero would win in a fight, or whether the Byzantine Empire was actually part of the Roman Empire or not, you're witnessing the same sport, and you're free to engage or not as you choose.

It got enough comments chewing it that it’s at least a byte

This is reductio ad absurdam.

Planetquake. Or just quake.

Incidentally, Sol isn't an 'official' name for our sun. The term 'solar power' is more like a brand-name that's been genericised.

> Of course no NASA person actually talks like this

Are you saying "The Martian" was inaccurate?

One could also feel a moonquake while looking at an earthrise.

How would one view an earthrise?

By going to the moon.

Did you miss a step? The moon doesn't have earthrises.

They're probably referring to this photo [0]. This effect was actually due to the fact they were on the spacecraft in motion, but it's apparently possible to have an earthrise near the edges of the Earth-visible portion of the moon, because the Moon isn't completely stationary relative to earth:

> Because the Moon is tidally locked with the Earth, one side of the Moon always faces toward Earth. Interpretation of this fact would lead one to believe that the Earth's position is fixed on the lunar sky and no earthrises can occur; however, the Moon librates slightly, which causes the Earth to draw a Lissajous figure on the sky. This figure fits inside a rectangle 15°48' wide and 13°20' high (in angular dimensions), while the angular diameter of the Earth as seen from Moon is only about 2°. This means that earthrises are visible near the edge of the Earth-observable surface of the Moon (about 20% of the surface). Since a full libration cycle takes about 27 days, earthrises are very slow, and it takes about 48 hours for Earth to clear its diameter.

[0] https://en.wikipedia.org/wiki/Earthrise

https://en.wikipedia.org/wiki/Earthrise

That's only from orbit. The Moon is tidally locked to Earth, so Earth remains in roughly the same spot in the sky.

It has a wobble. Near the limb or poles you would see an earthrise. This is shown in the beginning of the second season of For All Mankind btw.

Kim Stanly Robinson also hits on this in Red Moon. Someone is emotionally invested in having a particular plot of moon where the earth peeks out through a gap in a crater wall during the wobble.

There is some wiggle in the tidal lock so you could get an earthrise near the edge of the dark side.

Far side, you mean.

It does, but they are not the same as moonrises from earth.

Sure, in the sense that the Earth can never leave a small fixed area of the sky, that area of the sky generally doesn't include the horizon, and the Earth cannot be seen to move at all except over very long periods of time.

In other words, not only are they not the same, they are not similar in any way, nor is "rise" an applicable term.

of course does, it is just mostly stationary. so to view it in motion you have to move yourself from the far side to the nearside

omg, I'm an idiot sometimes. It's a wonder they let me anywhere near spacecraft.

It’ll blown your mind when you realize what “Geo” means.

(Geo is the Greek word for Earth)

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