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Gryphon
Gryphon
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Yes and no. You could establish two planets of that size in an orbital system of that range. You could establish two planets of ANY size in an orbital system of ANY range. However, in such a system, one body does not stay in place while the other orbits it. In any orbital system, what really happens is that the two bodies involved orbit a common centre of mass. (That is to say, the average position of all the mass in the two bodies.) In the Earth/Moon system, the Earth is so much more massive than the Moon that this centre of mass is inside the Earth, meaning that the Earth appears to move barely at all, while the Moon appears to orbit around it. However, if both bodies were of a similar mass, they would both orbit a point about half wayhalfway between the two of them. If you had a more massive planet and a less massive one, then the centre of mass would always be closest to the more massive one.

You seem to be asking whether you could weight a smaller planet with iron to make it more massive than a larger one, so that the larger planet has less mass. In the case of an Earth-sized planet and a Ganymede-sized one, a back-of-a-napkin calculation tells me that the Ganymede-sized one would need to be about 500 times as dense as the Earth-Sized one, simply for them to have the same mass. If you wanted their centre of mass to be inside the Ganymede-sized planet, it would need to be about 250 times as massive as the earth-sized one, making it (very approximately) 125,000 times as dense. Considering iron is only about 3 times as dense as granite, even if the entirety of one planet was made of iron and the other of rock, you could only achieve 3 times the density, instead of the 125,000 times you would need.

(Note that all the numbers I just spouted are probably only correct to the nearest order of magnitude, but that is good enough for what I needed them to show.)

However, at the end of the day, there is no problem having the two planets just orbiting a common centre of mass somewhere between the two. They would still be in an orbital system, which would work like any other orbital system. It is important to remember that one body never simply "orbits" another, but rather the two orbit EACHOTHEReachother in any orbital system, even one where the masses of the bodies are enormously disparate. There is never a parent body and a child body, but rather both bodies, orbiting in tandem.

Yes and no. You could establish two planets of that size in an orbital system of that range. You could establish two planets of ANY size in an orbital system of ANY range. However, in such a system, one body does not stay in place while the other orbits it. In any orbital system, what really happens is that the two bodies involved orbit a common centre of mass. (That is to say, the average position of all the mass in the two bodies.) In the Earth/Moon system, the Earth is so much more massive than the Moon that this centre of mass is inside the Earth, meaning that the Earth appears to move barely at all, while the Moon appears to orbit around it. However, if both bodies were of a similar mass, they would both orbit a point about half way between the two of them. If you had a more massive planet and a less massive one, then the centre of mass would always be closest to the more massive one.

You seem to be asking whether you could weight a smaller planet with iron to make it more massive than a larger one, so that the larger planet has less mass. In the case of an Earth-sized planet and a Ganymede-sized one, a back-of-a-napkin calculation tells me that the Ganymede-sized one would need to be about 500 times as dense as the Earth-Sized one, simply for them to have the same mass. If you wanted their centre of mass to be inside the Ganymede-sized planet, it would need to be about 250 times as massive as the earth-sized one, making it (very approximately) 125,000 times as dense. Considering iron is only about 3 times as dense as granite, even if the entirety of one planet was made of iron and the other of rock, you could only achieve 3 times the density, instead of the 125,000 times you would need.

(Note that all the numbers I just spouted are probably only correct to the nearest order of magnitude, but that is good enough for what I needed them to show.)

However, at the end of the day, there is no problem having the two planets just orbiting a common centre of mass somewhere between the two. They would still be in an orbital system, which would work like any other orbital system. It is important to remember that one body never simply "orbits" another, but rather the two orbit EACHOTHER in any orbital system, even one where the masses of the bodies are enormously disparate. There is never a parent body and a child body, but rather both bodies, orbiting in tandem.

Yes and no. You could establish two planets of that size in an orbital system of that range. You could establish two planets of ANY size in an orbital system of ANY range. However, in such a system, one body does not stay in place while the other orbits it. In any orbital system, what really happens is that the two bodies involved orbit a common centre of mass. (That is to say, the average position of all the mass in the two bodies.) In the Earth/Moon system, the Earth is so much more massive than the Moon that this centre of mass is inside the Earth, meaning that the Earth appears to move barely at all, while the Moon appears to orbit around it. However, if both bodies were of a similar mass, they would both orbit a point about halfway between the two of them. If you had a more massive planet and a less massive one, then the centre of mass would always be closest to the more massive one.

You seem to be asking whether you could weight a smaller planet with iron to make it more massive than a larger one so that the larger planet has less mass. In the case of an Earth-sized planet and a Ganymede-sized one, a back-of-a-napkin calculation tells me that the Ganymede-sized one would need to be about 500 times as dense as the Earth-Sized one, simply for them to have the same mass. If you wanted their centre of mass to be inside the Ganymede-sized planet, it would need to be about 250 times as massive as the earth-sized one, making it (very approximately) 125,000 times as dense. Considering iron is only about 3 times as dense as granite, even if the entirety of one planet was made of iron and the other of rock, you could only achieve 3 times the density, instead of the 125,000 times you would need.

(Note that all the numbers I just spouted are probably only correct to the nearest order of magnitude, but that is good enough for what I needed them to show.)

However, at the end of the day, there is no problem having the two planets just orbiting a common centre of mass somewhere between the two. They would still be in an orbital system, which would work like any other orbital system. It is important to remember that one body never simply "orbits" another, but rather the two orbit eachother in any orbital system, even one where the masses of the bodies are enormously disparate. There is never a parent body and a child body, but rather both bodies, orbiting in tandem.

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Arthur
Arthur
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Yes and no. You could establish two planets of that size in an orbital system of that range. You could establish two planets of ANY size in an orbital system of ANY range. However, in such a system, one body does not stay in place while the other orbits it. In any orbital system, what really happens is that the two bodies involved orbit a common centre of mass. (That is to say, the average position of all the mass in the two bodies.) In the Earth/Moon system, the Earth is so much more massive than the Moon that this centre of mass is inside the Earth, meaning that the Earth appears to move barely at all, while the Moon appears to orbit around it. However, if both bodies were of a similar mass, they would both orbit a point about half way between the two of them. If you had a more massive planet and a less massive one, then the centre of mass would always be closest to the more massive one.

You seem to be asking whether you could weight a smaller planet with iron to make it more massive than a larger one, so that the larger planet has less mass. In the case of an Earth-sized planet and a Ganymede-sized one, a back-of-a-napkin calculation tells me that the Ganymede-sized one would need to be about 500 times as dense as the Earth-Sized one, simply for them to have the same mass. If you wanted their centre of mass to be inside the Ganymede-sized planet, it would need to be about 250 times as massive as the earth-sized one, making it (very approximately) 125,000 times as dense. Considering iron is only about 3 times as dense as granite, even if the entirety of one planet was made of iron and the other of rock, you could only achieve 3 times the density, instead of the 125,000 times you would need.

(Note that all the numbers I just spouted are probably only correct to the nearest order of magnitude, but that is good enough for what I needed them to show.)

However, at the end of the day, there is no problem having the two planets just orbiting a common centre of mass somewhere between the two. They would still be in an orbital system, which would work like any other orbital system. It is important to remember that one body never simply "orbits" another, but rather the two orbit EACHOTHER in any orbital system, even one where the masses of the bodies are enormously disparate. There is never a parent body and a child body, but rather both bodies, orbiting in tandem.