There really is an xkcd for everything.
this post was submitted on 05 Aug 2025
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Damm Earth is big
Being a fan of The Expanse this is really cool. It really puts the size of a lot of the moons and dwarf planets from the series into perspective. Ganymede for example, was used by pregnant mothers in the outer-system because it was large enough to still have an active core and thus a magnetosphere. Shielding the surface from a lot of radiation. Their main food crops were grown there for the same reason.
Io, Callisto, Europa, Eris, Titan, Ceres, and a few others all make appearances too. It's an amazing series, for those who haven't read/seen it, whether you read the books or watch the show.
It’s generally a great series but it reminds me of Wheel of Time, in that some of the main characters are incredibly stupid and don’t seem to get any better. James Holden in particular is one whose stupidity is hard to withstand sometimes. I ended up not being able to finish both of those because of that.
Yeah, most of James' issues are just him trying to do the right thing. He tends to jump in head first at that point.
spoiler
Like him walking into a clearly radioactive room, despite warning signs being everywhere and a literal siren going off. All because he saw some injured/sick people lying on the ground and he didn't hesitate to help.
Or flying the ship into a pile of ruble looking for the hybrid (that doesn't happen in the book).
Holden's favourite book, if I recall correctly, is Don Quixote... but instead of seeing it as a satire of sixteenth century Spain and chivalric tradition he sees the antics of the evidently senile and deranged protagonist as a manual of how to act.
The whole series is Holden tilting at windmills.
They're quite well written and engaging windmills, though, and there's a lot of great Sancho Panzas to accompany and provide a contrast to our knight errand, so it's still a great series.
I guess it's easy to forget just how much smaller Mars is until comparisons like this help put it in perspective.
mars' surface area is approximately as big as earth's land surface area, i.e. everything excluding oceans. since oceans cover a large part of earth's surface, there's that.
I can't readily recall the Earth's actual sq. km surface area, and can't remember ever having heard the figure for Mars. Time to drop into Wikipedia and take a gander, I think.
EDIT: I'll be damned, TIL that the Earth has an area of 510.06 10^6 km², but Mars' is only 144.37 10^6 km², only about 1⁄3 the size (28.3%).
The circumference is roughly 40,000 kilometers. The original definition for a meter was such that 10,000 kilometers was the distance from the equator to the poles (so a quarter of the circumference). They got the math slightly wrong and didn't want to people to think the process was wrong so they didn't correct it. I forget the actual circumference but that is close enough for very rough estimates.
the distance from the equator to the poles is a quarter of the circumference
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Pangea is bigger than anyone thought. Cool.
TIL Ganymede is bigger than Mercury?
So is Titan.
Hard to say with the irregular shape, but they're close.
What really gets me is how small Mars is relative to Earth and Venus.
Kinda shows how useless the fantasy of living on Mars really is. Not only is this a barren wasteland, it's also a tiny barren wasteland.
I/3 the gravity as well, so watch out for that bone density
I mean, I wouldn't call it "useless". There's almost certainly a benefit to the science and technology that can move people to Mars safely and transform it into a habitable place.
But "We're going to Mars!" as a mission is a fantasy. "We're going to keep investing in blue sky research until we have advanced enough technology to make Mars a feasible destination" is where the money is at.
Where's jupiter
Isnt Jupiter mostly gas/liquid with only a solid core?
Does it even have a solid core?
probably? according to this diagram, it consists mostly of metallic hydrogen, which i interpret to mean "hydrogen in a solid phase".
Metallic Hydrogen apparently just means "hydrogen in a state that conducts electricity". No idea what kind of pressure and temperate would form actually solid hydrogen, but from my understanding the gas giants are quite hot internally.
And by that diagram the core would be massive.
From what I can see it's a diffuse core, meaning it's a gas until it isn't, but with no real line between the two.
yeah i read up on it and all four giants (jupiter, saturn, uranus, neptune) have no "clear" surface: they all have a gaseous atmosphere on the surface, but when you go down, it goes above the critical point and therefore continuously changes into a liquid phase with no clear line in between. very deep inside, they all have cores made from rocks, but it's rather small compared to the total size of the planet.
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Thank you! It looked very XKCD to me, so I was surprised when the source link wasn't to that.
Edit: oops... Meant to reply to the comment with the xkcd link.
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I guess fact it's mostly gas means I don't have to ask, "where's Uranus?"
But if we're counting the liquid parts of Earth, shouldn't we include the squashy centers of Uranus and Jupiter?
They aren't necessarily counting the oceans, but rather the ocean floor.
The "liquid parts" of earth are just a thin puddle over basically the same solid shell covering the rest of the planet, relatively speaking. Uranus does have a small rocky core (so probably should have been included tbh), but Jupiter's core is just liquid and doesn't even have a clear boundary between the gas and the core.
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Welp, there's my next TTRPG map.
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