If Jupiter’s gravity is only 2.5x that of the Earth, how is it the vacuum cleaner of the solar system?


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

surface gravity isn’t that important for acting as a “vacuum cleaner”. By the time something’s at the surface, the job is done. What’s more important is a sense of how much space it influences, and that’s determined by its mass.

Jupiter is 318 times as massive as earth. If earth’s “influence” dies off after, say, some distance, then Jupiter’s extends almost 18 times further, affecting a region of space over 5500 times as large as earth’s sphere of influence.

The only reason Jupiter’s “surface gravity” is comparable to earth’s is that as well as being massive, Jupiter is huge: its surface is over 10 times as far from the centre as earth’s is, so gravity there should be 100 times weaker, and yet it still manages to beat us.

Jupiter is 317 times more massive than Earth, which means that its gravitational force is 317 times stronger than that of the Earth.

One would then expect, all else equal, that the vast majority of random objects flying through space that don’t hit the sun would be far more likely to hit Jupiter than Earth.

Surface gravity here is a red herring.

The reason why the surface gravity of Jupiter is only 2.5x Earth is because the “surface” in that measurement is much further from the core of Jupiter than the Earth’s surface is from earth’s core.

Serious question: Does Jupiter even have a surface?

Only a little OT is my favourite comet story …

Comet Shoemaker-Levy 9 flew past Jupiter in 1992 and was broken into 21 fragments by Jupiter’s tidal gravity.

Two years later, the comet struck Jupiter. The largest fragment, fragment G, exploded with same force as 600x the Earth’s nuclear weapons, blasting a hole the size of the Earth in the atmosphere.

So we are lucky that Jupiter is such a good vacuum cleaner, since I wouldn’t be typing this if fragment G blew a hole the size of the Earth in the Earth itself.

It’s surface gravity. It’s much more massive but the surface is father from the center. As a whole it has way more gravitational pull. If it was shunk down to earth size with the same mass its gravity would be crushing.