Xelaya : The Impossible Planet
Posted: Sat Jan 12, 2019 1:06 am
So I was thinking about Xelaya and the gravity on the planet and how strong the people are.
Okay. First, Gordon throws a bottle onto the surface. It instantly flattens under its own weight. But we don't know what the bottle was made of or how thick it was. So we can't be terribly precise about that. But it can give you an idea, because no matter how advanced the future may be, surely they aren't making super-strong drinks bottles. I mean, what would be the point of that? So, just think about how many empty bottles you would expect to pile on top of one another before the bottom one was crushed. Hundreds, right? If not thousands?
Later we see that without his suit, Eds shin bones literally crush under their own weight. Now a shin bone might mass roughly half a kilo, and on Earth this would weigh about 5 Newtons. This discussion states that one cubic inch of human bone can withstand the weight of five pickup trucks. That's maybe 15 tons - roughly 150,000 Newtons.
Which would indicate that Xelaya's gravity was 300,000 Newtons per kilo... or about 30,000 x Earth gravity. That works in line with the bottle, because you'd certainly expect a stack of 30,000 bottles to be heavy enough that the bottom one would be crushed flat.
This leads to several problems!
1) If this is even close to true, then everything on Xelaya must be enormously strong. And I mean everything. We can imagine the future to have superstrong materials like steel and concrete. But Xalaya has couches with soft cushions. And clothing made of fabric. Every one of these must be made of materials so strong that in our gravity they'd feel like concrete.
2) Xelayans would have to be not just strong, but amazingly strong. Like, even a weakened Alara would be able to lift thousands of tons. That set of weights she was lifting in Home... did that look like a thousand tons to you?
3) As I've said, for a body of constant density the gravity at the surface increases linearly with the radius. Twice the size, twice the gravity. To account for the gravity, Xelaya would need to be 30,000 times the size of Earth. It sure didn't look that.
Of course, perhaps Xelaya is a denser planet. Xelaya could be a hundred times larger than Earth and three hundred times denser, perhaps?
The trouble with this is, materials only get so dense. Even if it were made of solid Uranium, the planet would only be four or five times denser than Earth, so it would need to be 6,000 times larger. Still not great.
So if it does have that high a gravity, this is a decidedly abnormal planet. (Worth pointing out here, the physics of planets in other solar systems is a science still in its infancy. Right now may be a LOT we don't know about what's possible.) Is it possible Xelaya is made of something exotic?
Let's take a white dwarf. This is what you get when your sun dies and it's not big enough to be a black hole or a neutron star star. The surface gravity of a white dwarf is immense. Sirius B, for instance, has about the mass of our Sun in a body about the size of our Earth. As a result, it has a gravity of about 440,000 g. Which is easily high enough - too high, actually.
4) So. Here's a wacky solution. Xelaya is an artificial planet.
Actually, what Xelaya is, is a sub-sized dyson sphere. Long in the past, somebody wanted to build a dyson style structure, but they couldn't build one around a whole full sun, an AU in diameter. So the built one around a white dwarf. And instead of living on the inside, they lived on the outside.
In the middle of Xelaya is a white dwarf, the size of the Earth and with a surface gravity of 440,000 g. At some point in the past, a race built a shell around it. The shell has a radius about 3.8 times the size of the white dwarf's, which reduces the gravity to a cosy 30,000 g. The aliens stocked it with superstrong materials and animals and such. And that's what Xelaya is; a fake planet. That's why it has rings, you know - that's the rubble left over from building it.
Maybe the Xelayans did this, and their species is older than we know. I tend to think not, because a species with that capability would be scary-advanced, which they aren't. So that species left, and the Xalayans we know evolved on the planet later.
Interesting idea, yes?
5) Incidentally, in Priya we saw that an Orville shuttle can't escape the gravity of a sun if it's too close. At the surface of our sun, the gravity is about 30g. The gravity on Xelaya is a thousand times greater than this, yet shuttles can handle it just fine. Interesting!
So those are my thoughts on Xelaya. Any comments?
Okay. First, Gordon throws a bottle onto the surface. It instantly flattens under its own weight. But we don't know what the bottle was made of or how thick it was. So we can't be terribly precise about that. But it can give you an idea, because no matter how advanced the future may be, surely they aren't making super-strong drinks bottles. I mean, what would be the point of that? So, just think about how many empty bottles you would expect to pile on top of one another before the bottom one was crushed. Hundreds, right? If not thousands?
Later we see that without his suit, Eds shin bones literally crush under their own weight. Now a shin bone might mass roughly half a kilo, and on Earth this would weigh about 5 Newtons. This discussion states that one cubic inch of human bone can withstand the weight of five pickup trucks. That's maybe 15 tons - roughly 150,000 Newtons.
Which would indicate that Xelaya's gravity was 300,000 Newtons per kilo... or about 30,000 x Earth gravity. That works in line with the bottle, because you'd certainly expect a stack of 30,000 bottles to be heavy enough that the bottom one would be crushed flat.
This leads to several problems!
1) If this is even close to true, then everything on Xelaya must be enormously strong. And I mean everything. We can imagine the future to have superstrong materials like steel and concrete. But Xalaya has couches with soft cushions. And clothing made of fabric. Every one of these must be made of materials so strong that in our gravity they'd feel like concrete.
2) Xelayans would have to be not just strong, but amazingly strong. Like, even a weakened Alara would be able to lift thousands of tons. That set of weights she was lifting in Home... did that look like a thousand tons to you?
3) As I've said, for a body of constant density the gravity at the surface increases linearly with the radius. Twice the size, twice the gravity. To account for the gravity, Xelaya would need to be 30,000 times the size of Earth. It sure didn't look that.
Of course, perhaps Xelaya is a denser planet. Xelaya could be a hundred times larger than Earth and three hundred times denser, perhaps?
The trouble with this is, materials only get so dense. Even if it were made of solid Uranium, the planet would only be four or five times denser than Earth, so it would need to be 6,000 times larger. Still not great.
So if it does have that high a gravity, this is a decidedly abnormal planet. (Worth pointing out here, the physics of planets in other solar systems is a science still in its infancy. Right now may be a LOT we don't know about what's possible.) Is it possible Xelaya is made of something exotic?
Let's take a white dwarf. This is what you get when your sun dies and it's not big enough to be a black hole or a neutron star star. The surface gravity of a white dwarf is immense. Sirius B, for instance, has about the mass of our Sun in a body about the size of our Earth. As a result, it has a gravity of about 440,000 g. Which is easily high enough - too high, actually.
4) So. Here's a wacky solution. Xelaya is an artificial planet.
Actually, what Xelaya is, is a sub-sized dyson sphere. Long in the past, somebody wanted to build a dyson style structure, but they couldn't build one around a whole full sun, an AU in diameter. So the built one around a white dwarf. And instead of living on the inside, they lived on the outside.
In the middle of Xelaya is a white dwarf, the size of the Earth and with a surface gravity of 440,000 g. At some point in the past, a race built a shell around it. The shell has a radius about 3.8 times the size of the white dwarf's, which reduces the gravity to a cosy 30,000 g. The aliens stocked it with superstrong materials and animals and such. And that's what Xelaya is; a fake planet. That's why it has rings, you know - that's the rubble left over from building it.
Maybe the Xelayans did this, and their species is older than we know. I tend to think not, because a species with that capability would be scary-advanced, which they aren't. So that species left, and the Xalayans we know evolved on the planet later.
Interesting idea, yes?
5) Incidentally, in Priya we saw that an Orville shuttle can't escape the gravity of a sun if it's too close. At the surface of our sun, the gravity is about 30g. The gravity on Xelaya is a thousand times greater than this, yet shuttles can handle it just fine. Interesting!
So those are my thoughts on Xelaya. Any comments?