Timeline for How can Ganymede have an Earth-like gravity without us having realized it?
Current License: CC BY-SA 4.0
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| Sep 24, 2018 at 0:34 | comment | added | user151841 | @EricDuminil Well that illuminates the other half of the problem. If Ganymede were the size of a soccer ball, but had the same mass, we wouldn't known it was there, and we would have had to figure out the mystery of the "missing moon" of Jupiter. We would have concluded there was a very dense, very small moon that had to be there, because of its gravitational effects on the orbits. However, if it's large enough that we can see it, we know it's there, and from seeing it, we can understand its orbit, and deduce its mass. There's really no way around it. We know it's there one way or the other. | |
| Sep 19, 2018 at 19:51 | comment | added | Eric Duminil | @user151841: If you replace Ganymede with a soccer ball of Ganymede's mass, nothing at all would change for Jupiter or the other moons. The only thing that would change would be the gravity at Ganymede's surface. The same thing happens (i.e. nothing) if the sun becomes a black hole. | |
| Sep 19, 2018 at 16:53 | comment | added | user151841 | @Jeffiekins it's not the gravity of Ganymede, but the us knowing about it is the problem. The gravity defines the orbit and its relationship with Jupiter and the other moons. T | |
| Sep 19, 2018 at 10:00 | comment | added | Eric Duminil | @nikie: Sure. I just wanted to point out that mass alone cannot be the only reason why it possibly wouldn't work. | |
| Sep 19, 2018 at 9:41 | comment | added | nikie | @EricDuminil: That's for an asteroid with 2m diameter. Ganymede is way bigger than that. | |
| Sep 19, 2018 at 7:02 | comment | added | Eric Duminil | It might be impossible, but not for the reason you mention. See "what if? little planet" | |
| Sep 18, 2018 at 20:32 | comment | added | Jeffiekins | Mass combines with radius to make gravity! If it were a lot smaller, it could have an Earth-like gravity. That's why the "variable density" idea is more workable: if there were a much more dense (i.e., small-radius) core and the "people" were near it, G would be much higher. | |
| Sep 18, 2018 at 14:41 | history | answered | Tim B | CC BY-SA 4.0 |