I was taught years ago that one of the many conditions that make the Earth stable enough for complex life is that our “big brother” Jupiter works as a vacuum cleaner, clearing out wayward comets and asteroids from the inner solar system so fewer of them have a chance to contact Earth. Makes sense, Jupiter is big.
I recently learned, however, that Jupiter’s “surface gravity” is only 2.5x that of the Earth. No offense to Jupiter, but that feels less like a Kirby and more like a Swiffer.
Is there some different measurement of gravity (other than “surface gravity) that I’m not aware of that’s doing the heavy lifting? Or is it possible that in another, hypothetically similar solar system, a rocky planet 2.5x the size of earth positioned roughly the same distance Jupiter is from Earth would do the same “vacuuming” work?
In: 1661
As there are already good answers, I hope a tangent is okay.
I occasionally see questions like “If a black hole were to pass near the Solar System, how could we avoid falling into it?” or “If most galaxies have a giant black hole at their core, why haven’t they already swallowed everything?” I am reminded of such questions because this one shows the same misunderstanding in reverse. Gravity at the ‘surface’ of a black hole is effectively infinite, but that only matters if you’re near the surface.
To the first of the questions I quoted, the answer is: same way we avoid falling into the Sun, but easier (even though, according to current theory, the smallest black hole is more than twice as massive as Sol) because it is a much smaller target. (But see Greg Egan’s short novel *Perihelion Summer* for a better reason to be afraid.)
To the second: the core singularity is huge, yes, but it’s also very far from us.
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