# 5 of 8 planets in our solar system have gravity apx 1 G. Reason? **URL:** \ **Category:** Factual Questions\ **Created:** [July 6, 2015, 11:22am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388 "2015-07-06T11:22:15Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 6, 2015, 9:47pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/21 "2015-07-06T21:47:23Z")
While we’re at it: If you dig a deep hole in the Earth, the gravity will be almost constant at any depth, all the way until you get to the edge of the core. This is due to variations in the density of the mantle. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [July 6, 2015, 9:52pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/22 "2015-07-06T21:52:45Z")
> [@billfish678](#): > > Whats the G level at the “surface” of the sun? About 28 gees. > [@](#): > > 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. That’s only true for gas giants Saturn-sized and smaller. Jupiter is denser and has a gravity 2.53 x Earth; gas giants that are more massive than Jupiter will be even more dense, and will have even greater gravity levels at the top of the atmosphere (assuming constant temperature). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 6, 2015, 10:47pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/23 "2015-07-06T22:47:06Z")
More to the point, gas giants that are more massive than Jupiter will even have smaller radii. Jupiter is very near the maximum possible radius for a gas giant. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [July 6, 2015, 10:53pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/24 "2015-07-06T22:53:23Z")
Something wonderful is going to happen. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [July 6, 2015, 10:57pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/25 "2015-07-06T22:57:41Z")
Taking the gas giants out of it, since their ‘surface’ is chosen specifically to provide a common rule, the 1g thing only includes Earth and Venus. Mercury and Mars do not fit the pattern. Around other star systems we have found rocky planets and gas giants of many different sizes and densities with widely varying surface gravity. So I would rather chalk up the relative similarity between Earth and Venus as a coincidence. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 6, 2015, 11:04pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/26 "2015-07-06T23:04:53Z")
> [@GusNSpot](#): > > 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. ) Neutron stars do this, essentially, with something like 20 billion times earth’s gravity at the surface. You won’t see it happen anywhere in our solar system, though. ---
**Author:** ![Skald\_the\_Rhymer](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Skald\_the\_Rhymer](https://boards.straightdope.com/u/Skald_the_Rhymer)\ **Post date:** [July 6, 2015, 11:17pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/27 "2015-07-06T23:17:30Z")
> [@chacoguy](#): > > According to Star Trek, all planets have exactly 1 G, You jest, of course. But Vulcan canonically has higher gravity than Earth. And the other planets we are are self-sorting; there’s enough terrestrial planet in the Trek galaxy that Starfleet only bothers with the Class Ms – those with gravity, temperature, and atmosphere compatible with humanoid life. ---
**Author:** ![Teach-me-not](https://avatars.discourse-cdn.com/v4/letter/t/a4c791/32.png) [@Teach-me-not](https://boards.straightdope.com/u/Teach-me-not)\ **Post date:** [July 7, 2015, 1:04am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/28 "2015-07-07T01:04:18Z")
Very minor nitpick. G (in caps) is the universal gravitational constant that appears in Newton’s law of gravitation. This has nothing to do with the earth per se. OTOH, g (small letters) is the familiar acceleration due to gravity (i.e., the weight of a unit mass) on the surface of the earth. Thus, for example, the surface gravity on Jupiter is about 2.5 g, not 2.5 G. The two quantities are related (by Newton’s law of gravitation), but they aren’t quite the same. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [July 7, 2015, 2:01am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/29 "2015-07-07T02:01:45Z")
> [@dracoi](#): > > Neutron stars do this, essentially, with something like 20 billion times earth’s gravity at the surface. You won’t see it happen anywhere in our solar system, though. Yes, but it was specified that the moleccular structure wouldn’t change, and being on the surface of a neutron star would definitely change that. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 7, 2015, 2:16am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/30 "2015-07-07T02:16:45Z")
> [@billfish678](#): > > Something wonderful is going to happen. Umm…can give us a hint? Did it already happen and I missed it? Did you intend that for this thread? Maybe you didn’t intend to type it at all, but you were in such a good mood you thought you were just thing aloud? ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [July 7, 2015, 2:21am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/31 "2015-07-07T02:21:34Z")
> [@Leo\_Bloom](#): > > Umm…can give us a hint?. . . . How about. . . It’s a movie sequel, and the numerals in the title are the same as its predecessor, but rearranged. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [July 7, 2015, 2:39am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/32 "2015-07-07T02:39:27Z")
> [@billfish678](#): > > Something wonderful is going to happen. Attempt no landings there. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [July 7, 2015, 4:25am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/33 "2015-07-07T04:25:22Z")
> [@Andy\_L](#): > > Attempt no landings there. But … it’s full of stars … ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [July 7, 2015, 10:25am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/34 "2015-07-07T10:25:30Z")
Going back to the 1g gas/ice giants. It was noted that a surface and a surface gravity was ‘assigned’ at a certain level, thus perhaps not 1g. It also seems like this ‘altitude’ is a place where pressure quickly increases so not unreasonable to assign a ‘surface’ level there, it may be a place where we can float something one day. But what would be the gravity distribution vs. depth then. In the center it is zero, it would rise to a certain level then fall again. Where is the 1g in this distribution? What would be the ‘correct’ g to give them? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [July 7, 2015, 11:36am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/35 "2015-07-07T11:36:27Z")
That’s an interesting question. This graph (which is only very approximate) shows how the gravity of various planets increases with depth. [![](http://cseligman.com/text/planets/gravity2.jpg) ](http://cseligman.com/text/planets/gravity2.jpg) Earth has a small peak just at the core/mantle boundary, while Jupiter and Saturn have massive peaks at the boundary between the rocky core and the metallic/hydrogen mantle. Saturn has a gravity level of 1.065 g at the (arbitrary) level defined by 1 bar of pressure. To get to 1g you’d have to go a little higher. So a rough answer to your question “Where is the 1g in this distribution?” is a/ somewhere in the core and b/ somewhere slightly above the arbitrarily defined ‘surface’. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [July 7, 2015, 11:46am UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/36 "2015-07-07T11:46:09Z")
One thing we haven’t accounted for on Saturn is the rapid rotation. At the equator, the perceived gravity level would only be 0.9 g, because of centrifugal force. The slightly flattened poles have slightly higher gravity too, about 1.2 . So you could find a one g latitude on Saturn somewhere between the equator and the poles. ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [July 7, 2015, 12:26pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/37 "2015-07-07T12:26:16Z")
> [@eburacum45](#): > > That’s an interesting question. This graph (which is only very approximate) shows how the gravity of various planets increases with depth. > [http://cseligman.com/text/planets/gravity2.jpg](http://cseligman.com/text/planets/gravity2.jpg) > Earth has a small peak just at the core/mantle boundary, while Jupiter and Saturn have massive peaks at the boundary between the rocky core and the metallic/hydrogen mantle. > > Saturn has a gravity level of 1.065 g at the (arbitrary) level defined by 1 bar of pressure. To get to 1g you’d have to go a little higher. So a rough answer to your question “Where is the 1g in this distribution?” is > a/ somewhere in the core and > b/ somewhere slightly above the arbitrarily defined ‘surface’. Could you give a link to the page where that jpeg is found, rather than the jpeg itself? I’m getting an error message, and while I’ve poked around Seligman’s website, I haven’t found this table. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [July 7, 2015, 12:26pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/38 "2015-07-07T12:26:37Z")
> [@Earl\_Snake-Hips\_Tucker](#): > > How about. . . It’s a movie sequel, and the numerals in the title are the same as its predecessor, but rearranged. **Star Trek VI: The Undiscovered Country**? ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [July 7, 2015, 12:28pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/39 "2015-07-07T12:28:18Z")
> [@eburacum45](#): > > One thing we haven’t accounted for on Saturn is the rapid rotation. At the equator, the perceived gravity level would only be 0.9 g, because of centrifugal force. “You mean centripetal force. There’s no such thing as centrifugal force.” [Sorry, couldn’t resist](https://xkcd.com/123/). 😉 ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [July 7, 2015, 2:05pm UTC](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388/40 "2015-07-07T14:05:05Z")
> [@RTFirefly](#): > > Could you give a link to the page where that jpeg is found, rather than the jpeg itself? I’m getting an error message, and while I’ve poked around Seligman’s website, I haven’t found this table. > **[The Internal Pressures of the Planets](https://cseligman.com/text/planets/internalpressure.htm)** > > Discussion of the internal pressures of the planets, using relatively simple math and diagrams to explain the topic [Previous page](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388.md?page=1) [Next page](https://boards.straightdope.com/t/5-of-8-planets-in-our-solar-system-have-gravity-apx-1-g-reason/724388.md?page=3)