Venus Earth Saturn, Uranus & Neptune all have have gravity in the general range of 1 G. Is there a known reason or theory for why a majority of planets seemed to ‘mature’ at this level? and vastly different types of planets from rocky planets, to gas and ice giants.
Does this speak to the starting density of the solar system as it formed? Or perhaps what forms a planetary neighborhood size (‘neighborhood’ as used in terms of the IAU definition of ‘Planet’) which would lead to the spacing between planets? Is it related to the gravity of the sun? Is it just one of those happy coincidences that God did so when we learn to terraform we have other worlds to live on (unexplainable)?
Continuing…
Can we expect this trend on other star systems, and would that be around 1 G or based on conditions of their star system formation (gravity/density/spin) and perhaps have gravity tending towards a different number?
Being that Saturn , Uranus, and Neptune are gas giants with no surface to speak of, the similarity would seem to be wholly fortuitous.
Venus is something different, since it is a solid mass with nearly the same density, size, and gravity. I recall some texts calling it “Earth’s twin” (although, of course, circumstances beyond that, including the atmosphere, chemical composition, and proximity to the sun make an inhospitable “twin”.
Exactly what the significance is, though, I don’t know. Back when people thought the planets might have been formed by matter being pulled from the sun by a passing star, it was suggested that the similarity bolstered that explanation, with similar effects causing the similarity. Today it would probably be put down to similarities in eddy formation in the condensing rings of matter, or something.
I’m a little confused here. Having much greater masses than Earth, I had thought that the gas giants mentioned in the OP would have much greater gravitational pull. Off to Google.
OK, so it’s surface gravity that’s in question here. So if one were as close to Saturn’s center as we are to Earth’s center (~3,960 miles), we would, indeed, be subject to far more than 1g, correct?
G. David Nordley wrote an article on this topic (titled “Quantized Surface Gravity?!”) for Analog back in the early 1990s. You can probably find it online at Nordley’s website.
Gravity is a function both of total mass and of the distance from that mass. Gas giants are so much less dense than Earth - many of them average a lower density than water at 1 specific gravity. The Earth is something like 5 times more dense on average if memory serves, about 5 specific gravity. Walking around on a gas giant puts you pretty far from most of that mass compared to walking around on Earth.
To follow up on Cal’s point: While there is no clear surface to something like a gas giant, we do have an arbitrary definition for surface. From Wikipedia for Jupiter: “As Jupiter has no surface, the base of its atmosphere is usually considered to be the point at which atmospheric pressure is equal to 1 MPa (10 bar), or ten times surface pressure on Earth.” I didn’t see a similar definition for other planets, though, and I’m not sure if this is just an arbitrary number or if there is some difference in physical properties at that pressure that matters.
My WAG.
When you have a gas giant, I suspect the way the physics works out, until you get really big (or really small), 1 G is pretty much how its gonna play out.
For small rocky planets, that’s not the case. The only reason Venus and Earth are close is because they are darn close to the same size.
So, Venus and Earth being close is mild coincidence. Both of those being close to what your typical gas giant would be is another mild coincidence.
But even that coincidency doesn’t look that coincidency when you look at how much in the solar system ISN’T 1 g ish.
I suppose, but the pressure would be crushing.
There is the fact, if you could go to the center of a planet, you’d be weightless since all the planet’s mass would be all around you. I’m not sure how those dynamics would balance out in gas giants, though?
Further Googling says the “surface” of Saturn is defined as where the pressure = 1 bar = Earth’s surface atmospheric pressure. How strong is the gravity on Saturn? | Cool Cosmos
So we don’t have consistent standards on how the surface of various gas giants is defined. It starts to smell to me like the OP’s question amounts to a tautology.
IOW, I speculate that the planetary scientists select a definition of “surface” for gas giants which is related to Earth atmosphere pressure. Which coincidentally means the gravity at that point will be ~1G net of differences in atmospheric composition between the various planets.
As to Venus & Earth, we should also consider that before the big impact which spawned the Moon Earth had more mass and presumably more gravity.
Not necessarily. As you go further in, there is more mass above you, partially cancelling the force of gravity from the rest of the planet under you. There’s no rule, it depends on the density of the planet and how that density changes from the center to the outer surface. When you reach the center, you would be weightless (though crushed to death – let’s consider a hypothetical human made of adamantium who doesn’t need air and light and water).
If the mass of Saturn were squished into the same volume as the earth, then yes, you would be subject to far more than 1g at its “surface”.
At first glance yes.
But not really. If you descend into a gas giant, the pressure will go from “thinner than the top of Everest” to “Ungodly high pressure” in not that many miles. Not enough miles difference on the scale of the planet to make any significant difference in what the G level is at the altitude.
According to Star Trek, all planets have exactly 1 G,
Saturn probably has a small rocky core, where the gravity could be more than 3 gees. The gravity at the top of the atmosphere is much lower. Jupiter also probably has a core of similar size and gravity, but the gravity at the top of the atmosphere is higher than Saturn’s because the atmosphere is more massive. It seems that the density of the atmosphere is the most important factor here.
Whats the G level at the “surface” of the sun?
Seems to me part of the issue is that there really isn’t a large range of possible G levels for a gas giant in the first place, so anything possible will be sorta close to 1 G in the first place.
Surface gravities (relative to Earth’s) of some known rocky exoplanets located in their star’s habitable zone:
Gliese 581g: 1.33
Gliese 581d: 1.43
Gliese 667Cc: 1.36
Kepler 22b: 1.45
HD40307g: 1.42
HD85512b: 1.38
Gliese 163c: 1.39
Can an lander that leaks like a sieve and has no compressible parts go to the center or rocky surface of a gas giant but would have to be made very flat due to the massive gravity that will pull any appendages above the surface to flatness on the surface or the back of the main go cart? GoPro on a stick will be right out… correct? ( lets leave indestructible & irresistible on the plant “Unicorn” for now )
Gauss’s law means that only the mass in the sphere beneath you matters, assuming spherical symmetry.
Side question: Other than maybe a black hole, any place with a gravity so strong that can flatten a steel block into a thin, wide disc of steel metal without changing is basic molecular structure? ( It will test out as the same kind & grade of steel. )
Dude, just go to Lowes and be done with it.