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.
> 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.
In recent years this hypothesis has been disputed by some of the experts, but there are still some experts — people that know better than you or I — that say it still holds water. So take that for what it’s worth.
From what I understand about the only things most of the experts agree on that support complex life are: A star that doesn’t tidally lock its planets, the host planet being large enough to retain an atmosphere, the host planet being at the right distance to support liquid water, the host planet containing phosphorus in the mantle, the host planet containing a certain amount of oxygen, and the host planet having a moon to stabilize its rotation.
> Jupiter’s “surface gravity” is only 2.5x that of the Earth
“Surface gravity” on a planet like Jupiter is kinda meaningless because there is no “surface” (that isn’t some fairly arbitrary definition).
It’s possible you’re misremembering your statistics.
More likely, this is what you learned: Jupiter’s mass is 2.5 times that of all the other planets in the Solar System *combined.* [source:Wikipedia](https://en.wikipedia.org/wiki/Jupiter_mass)
The Sun makes up 99.85% of the total mass in the Solar System.
The Sun is 1st; Jupiter, a very distant 2nd; everything else, basically debris.
Call me pessimistic, but I’ve always seen this idea of Juptier as some great gravitational protector as premature.
It only takes 1 gravity sling to launch an asteroid or comet straight at us. Then it aint looking so friendly.
The **surface gravity** of Jupiter is hard to guess, as it is a gas planet.
Its [mass is 318 times that of earth](https://solarsystem.nasa.gov/planets/jupiter/in-depth/), so its gravity would be 318 times more than earth’s. (assuming gravitational effects are linear with total mass and no weird quantum stuff going on at high mass.)
It is also much bigger in volume (say the difference between cleaning with a Q-tip vs a Swiffer) but in the vastness of space this is barely noticeable. Jupiter is 11 times wider than Earth.
Gravitational attraction is “inversely proportional to the square of the distance between objects”. That means that things getting close to Jupiter (but still far from the sun) **will have Jupiter be the largest gravitational force acting on it**.
The 4 inner planets have very close orbits to the sun, and then Jupiter is very far out. This gives Jupiter a large range of space where it is the biggest local gravitational effect. One sign of this is that Jupiter has 80 moons. (It also has rings discovered in 1979)
Take the classic analogy of gravity as a heavy ball that curves a sheet of fabric. The slope of the fabric at any point is the gravitational force at that point. Jupiter’s “slope” at the surface of the ball might not be much steeper than Earth’s at its surface, but it extends further out so it can pull in objects that are further away.
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