# Gravity in the solar system
**URL:** https://boards.straightdope.com/t/gravity-in-the-solar-system/744208
**Category:** Factual Questions
**Created:** [January 25, 2016, 9:39pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208 "2016-01-25T21:39:32Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Henga](https://boards.straightdope.com/u/Henga)
#### Post date: [January 25, 2016, 9:39pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/1 "2016-01-25T21:39:32Z")
How much of the solar system had to be formed in order for a planet like the earth to establish a stable orbit around the sun? Could something like the earth have an orbit around the sun if the solar system had no other planets and moons to counter the sun’s gravitational attraction? Would the earth crash into the sun or fly off into space if it was by itself?
Also, if the planets were formed by space dust from the Big Bang accumulating together by gravity, what caused the original gravitational attraction that was needed to form each planet’s core? What kept the dust from being siphoned off by larger objects that already existed?
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### Author:  [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)
#### Post date: [January 25, 2016, 9:50pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/2 "2016-01-25T21:50:46Z")
> [@Henga](#):
>
> Could something like the earth have an orbit around the sun if the solar system had no other planets and moons to counter the sun’s gravitational attraction?
The other planets have only a small effect on Earth’s orbit. They don’t “counter” the sun’s gravity.
You could have a stable solar system that consisted of just a star and a single planet. The planet doesn’t crash into the star because it’s going too fast. It doesn’t shoot off into space because the star’s gravity is pulling on it. The two effects cancel out to produce a (roughly) circular orbit.
Here’s another way to think about it: The earth is always falling toward the sun and missing.
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### Author:  [@Telemark](https://boards.straightdope.com/u/Telemark)
#### Post date: [January 25, 2016, 9:51pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/3 "2016-01-25T21:51:26Z")
The sun is 3 orders of magnitude more massive than all the planets combined, and more than half of that is Jupiter. The planets and moons don’t counter the sun’s mass in any meaningful way. There’s no reason a lone planet couldn’t orbit a star in a stable orbit.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [January 25, 2016, 9:51pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/4 "2016-01-25T21:51:27Z")
The gravity of the Sun is what’s necessary to keep something in orbit around the Sun. The other planets are basically irrelevant.
And what caused the gravitational attraction between the bits of matter that formed a planet was the bits of matter that formed the planet. Again, the existence of other planets was basically irrelevant.
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [January 25, 2016, 10:17pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/5 "2016-01-25T22:17:12Z")
In fact, the other planets make the Earth’s orbit _less_ stable.
Play with this to see what I mean: [Super Planet Crash - Can you feel the gravity?](http://www.stefanom.org/spc/)
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [January 25, 2016, 11:49pm UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/6 "2016-01-25T23:49:53Z")
Or, more precisely, they _can_ make orbits less stable. Our actual Solar System is stable, but that’s because all those planets who couldn’t play nice have already been kicked out of the club.
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### Author:  [@panache45](https://boards.straightdope.com/u/panache45)
#### Post date: [January 26, 2016, 12:14am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/7 "2016-01-26T00:14:46Z")
> [@Henga](#):
>
> Also, if the planets were formed by space dust from the Big Bang . . .
Although the Big Bang occurred about 13.8 billion years ago, the solar system is only about 4.6 billion years old. So the dust that comprised the solar system was from an older star that had exploded, and that older star may have been formed by the explosion of a still older star. This is responsible for the existence of heavy metals on our planet, which didn’t exist directly from the Big Bang.
We are all just star dust.
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### Author:  [@Henga](https://boards.straightdope.com/u/Henga)
#### Post date: [January 26, 2016, 1:08am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/8 "2016-01-26T01:08:35Z")
If it takes the earth’s motion to counter the sun’s gravity so the earth doesn’t crash into the sun, what causes the earth’s motion if not the gravitational pull of everything else in the solar system?
If the earth’s solar system is made from matter left behind by an exploding star, is the matter older than the earth itself so the earth appears to be older than it really is?
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### Author:  [@Telemark](https://boards.straightdope.com/u/Telemark)
#### Post date: [January 26, 2016, 1:25am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/9 "2016-01-26T01:25:36Z")
The particles that make up the solar system had rotational motion before the planets and sun formed. While the planets do exert gravitation pull on the earth they don’t provide significant force. The earth keeps orbiting the sun because it is a stable orbit, it doesn’t need a pushing force to keep moving. It will slow down over eons, but for now we just keep spinning away.
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [January 26, 2016, 1:30am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/10 "2016-01-26T01:30:02Z")
> [@Henga](#):
>
> If the earth’s solar system is made from matter left behind by an exploding star, is the matter older than the earth itself so the earth appears to be older than it really is?
Individual atoms don’t have identifying ages. The Earth as a whole does. The age of the Earth is only meaningful from a time when the Earth as an identifiable object existed.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [January 26, 2016, 1:53am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/11 "2016-01-26T01:53:20Z")
This is pretty approachable: [Formation and evolution of the Solar System - Wikipedia](https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Formation)
Really crushing it down to a 3-line sketch …
Everything is swirling a bit in the beginning when it’s just a dust cloud. And as it condenses, that angular momentum is conserved. So the whole shebang ends up rotating. Eventually a band in a rotating cloud condenses into an orbiting solid body.
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### Author:  [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)
#### Post date: [January 26, 2016, 2:20am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/12 "2016-01-26T02:20:26Z")
> [@Henga](#):
>
> If the earth’s solar system is made from matter left behind by an exploding star, is the matter older than the earth itself so the earth appears to be older than it really is?
How old do you think the Earth is?
Stranger
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [January 26, 2016, 2:22am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/13 "2016-01-26T02:22:24Z")
> [@Henga](#):
>
> Also, if the planets were formed by space dust from the Big Bang accumulating together by gravity, what caused the original gravitational attraction that was needed to form each planet’s core?
Random differences in the thickness of the original dust cloud. Slightly thicker areas of dust had more gravity, which increased local gravity and pulled in more dust, which pulled in even _more_ dust, etc. Once started it became a cycle that fed on itself.
As to what caused that initial difference in dust density, it was probably a nearby supernova. Supernovas can cause a burst of star formation due to the shockwave from their detonation disturbing the local interstellar dust, as well as adding its own exploded mass.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [January 26, 2016, 2:40am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/14 "2016-01-26T02:40:54Z")
> [@](#):
>
> Quoth **Henga** :
>
> If it takes the earth’s motion to counter the sun’s gravity so the earth doesn’t crash into the sun, what causes the earth’s motion if not the gravitational pull of everything else in the solar system?
Your question is incorrect. Motion does not have nor need a cause.
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### Author:  [@Some\_Call\_Me.Tim](https://boards.straightdope.com/u/Some_Call_Me.Tim)
#### Post date: [January 26, 2016, 2:59am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/15 "2016-01-26T02:59:06Z")
> [@Chronos](#):
>
> Your question is incorrect. Motion does not have nor need a cause.
An object at rest, **cannot be stopped**!
- The Evil Midnight Bomber what Bombs at Midnight
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### Author:  [@Henga](https://boards.straightdope.com/u/Henga)
#### Post date: [January 26, 2016, 3:28am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/16 "2016-01-26T03:28:35Z")
> [@Stranger\_On\_A\_Train](#):
>
> How old do you think the Earth is?
>
> Stranger
Nobody was around when it formed, so I don’t see how anybody can know with any kind of certainty.
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### Author:  [@Henga](https://boards.straightdope.com/u/Henga)
#### Post date: [January 26, 2016, 3:34am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/17 "2016-01-26T03:34:42Z")
> [@Some\_Call\_Me.Tim](#):
>
> An object at rest, **cannot be stopped**!
>
> - The Evil Midnight Bomber what Bombs at Midnight
An object at rest can’t be set in motion unless a force acts on it. A moving object can’t change its direction unless a force acts on it.
Assuming that the Big Bang was an explosion in a vacuum, wouldn’t the mass and energy created by it have been sent equally in all directions? Why wouldn’t this mass and energy still be evenly distributed throughout the universe?
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [January 26, 2016, 3:56am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/18 "2016-01-26T03:56:20Z")
> [@Henga](#):
>
> An object at rest can’t be set in motion unless a force acts on it. A moving object can’t change its direction unless a force acts on it.
The earth (and other planets) likely formed as part of a spinning disk of matter. So it has always been in motion.
> [@](#):
>
> Assuming that the Big Bang was an explosion in a vacuum, wouldn’t the mass and energy created by it have been sent equally in all directions? Why wouldn’t this mass and energy still be evenly distributed throughout the universe?
Big Bang was not really an “explosion in vacuum,” since there was no vacuum to explode into before the Big Bang.
Anyway, all it takes is minute disturbances in the distribution. At large scales, gas clouds are unstable. If you compress it just a little bit, it starts to contract by its own gravity. And no gas cloud is perfectly still; it has a tiny bit of angular momentum. This gets amplified as it contracts, until a disk of spinning gas is formed around the newly formed star.
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### Author:  [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)
#### Post date: [January 26, 2016, 3:57am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/19 "2016-01-26T03:57:54Z")
> [@Henga](#):
>
> Assuming that the Big Bang was an explosion in a vacuum, wouldn’t the mass and energy created by it have been sent equally in all directions? Why wouldn’t this mass and energy still be evenly distributed throughout the universe?
This is a terrible assumption. The Big Bang was unequivocally NOT an explosion in a vacuum. It was an expansion of space-time itself.
Random chance and quantum fluctuations are sufficient to ensure that the mass inside the universe formed local variations. This [picture](http://www.nasa.gov/images/content/403322main_COBEallsky_full.jpg) from the COBE satellite of early universe residual background radiation shows how clumps formed, which eventually became galaxies.
We have an excellent broad understanding of how galaxies and then the Earth itself formed: multiple branches of science have been working decades to add to the picture.
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### Author:  [@Henga](https://boards.straightdope.com/u/Henga)
#### Post date: [January 26, 2016, 5:00am UTC](https://boards.straightdope.com/t/gravity-in-the-solar-system/744208/20 "2016-01-26T05:00:50Z")
> [@scr4](#):
>
> The earth (and other planets) likely formed as part of a spinning disk of matter. So it has always been in motion.
> Big Bang was not really an “explosion in vacuum,” since there was no vacuum to explode into before the Big Bang.
What produced the Big Bang if space didn’t exist before the Big Bang? Just how did the Big Bang also produce space?
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