Gravity in the solar system

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?

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.

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.

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.

In fact, the other planets make the Earth’s orbit less stable.
Play with this to see what I mean:

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.

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.

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?

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.

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.

This is pretty approachable:

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.

How old do you think the Earth is?


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.

Your question is incorrect. Motion does not have nor need a cause.

An object at rest, cannot be stopped!

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Nobody was around when it formed, so I don’t see how anybody can know with any kind of certainty.

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?

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.

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.

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 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.

What produced the Big Bang if space didn’t exist before the Big Bang? Just how did the Big Bang also produce space?