Why is the earth's axis tilted?
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07-10-2014, 03:50 PM (This post was last modified: 07-10-2014 04:29 PM by smileXsmileXsmile.)
Why is the earth's axis tilted?
The Neil DeGrasse Tyson version of cosmos said this in season1 episode 9 @32min

"the gravitation pull of venus, small but close, and that of jupiter, distant but massive, tilted the earth's axis this way and that. It ever so slightly tweaked the shape of its orbit."

Is this true? I always thought the earth's tilted axis was a result of asteroid impacts during formation, perhaps the one that split the moon and earth, I don't know. In fact I looked it up and found multiple sources that say the same thing, the tilted axis is because of asteroids. Any one know the answer? Is it because of venus and jupiter's gravity or asteroids? Maybe cosmos is wrong or no one knows?

"If you cannot explain it simply, you don't understand it enough" -Albert Einstein
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07-10-2014, 03:58 PM
RE: Why is the earth's axis tilted?
I don' t think it was the multiple asteroid impacts.

I remember reading some astrophysicist's talk about terra-forming Venus and they made the claim there isn't enough residual mass just 'floating around' in the solar system (Asteroids from the belt, Oort cloud) with which to impact Venus enough to start it spinning back up again. Even if we used a metric huge ton of energy gathering all said loose mass together and slamming it into Venus.

The message being that 'Planets = BIG'

As for the Moon impactor?

Does the Moon's orbit follow along the equator, or near to it? That might go a ways to answering the point about it adding/causing/being part of the manifestation of the tilt.

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07-10-2014, 04:22 PM
RE: Why is the earth's axis tilted?
The angular momentum imparted by collisions is not nearly enough to significantly alter the overall rotation of a planet.

Without going back to check for myself, it sounds like the quote you've pulled relates more to the eccentricity of the Earth's orbit, and not its axial tilt (it's spin motion and it's orbital motion being, for many purposes, essentially decoupled).

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07-10-2014, 04:22 PM (This post was last modified: 07-10-2014 05:02 PM by smileXsmileXsmile.)
RE: Why is the earth's axis tilted?
(07-10-2014 03:58 PM)Peebothuhul Wrote:  I don' t think it was the multiple asteroid impacts.

I remember reading some astrophysicist's talk about terra-forming Venus and they made the claim there isn't enough residual mass just 'floating around' in the solar system (Asteroids from the belt, Oort cloud) with which to impact Venus enough to start it spinning back up again. Even if we used a metric huge ton of energy gathering all said loose mass together and slamming it into Venus.

The message being that 'Planets = BIG'

As for the Moon impactor?

Does the Moon's orbit follow along the equator, or near to it? That might go a ways to answering the point about it adding/causing/being part of the manifestation of the tilt.

Much cheers to all.

yes i certainly agree that planets are big but planets can also be molten. (now that i think about it that's a lot of molten to impact through) but that is how the moon was formed right? The moon is only 1/4 of earths size, which is a pretty big impact. I'm not sure if it's enough of an impact, that i don't know. Any one got any good sources?

Ahhh good call about the moon relative to the equator. Given the fact that solar eclipses are rare, the moon must rotate perpendicular to the equator.

Therefore, asteroid impact started the initial rotation during formation, gravity tilted the axis. the axis was going so fast that when the 'moon impactor' hit earth, a chunk (the moon) broke off relative to equator? Is that right? Let me know

So back to the original question, how did jupiter and venus cause the earth's tilted axis? (please see my response to cjlr before answering)

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07-10-2014, 04:24 PM
RE: Why is the earth's axis tilted?
I also should disclaim that I only did a Google search and looked at the top results. So I'll rephrase and say: Those are my sources and I don't have any credible sources, before I make myself looks stupid lol

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07-10-2014, 04:56 PM (This post was last modified: 07-10-2014 05:10 PM by smileXsmileXsmile.)
RE: Why is the earth's axis tilted?
(07-10-2014 04:22 PM)cjlr Wrote:  The angular momentum imparted by collisions is not nearly enough to significantly alter the overall rotation of a planet.

Without going back to check for myself, it sounds like the quote you've pulled relates more to the eccentricity of the Earth's orbit, and not its axial tilt (it's spin motion and it's orbital motion being, for many purposes, essentially decoupled).

eccentricity in two dimensions wouldn't be a factor, but the slight angle of that eccentricity, in the third dimension might. All three planets must have their own somewhat angled eccentric orbit in the third dimension. There's also the factor of where Jupiter, Earth, and Venus lie on the z-axis.

But then again, isn't the earth's 23% tilt too extreme for venus, earth, and jupiter being "pretty much" being on the same (3 dimensional) plane? It might not be I don't know.


I'm dumbfounded. Can you, or anyone explain?

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07-10-2014, 05:25 PM
RE: Why is the earth's axis tilted?
I don't remember where I read or heard this.
One theory I'm most familiar with is the impactor theory.
The early proto-Earth was hit with another planetoid roughly the size of Mars. The reason both were not completely destroyed is because it was an off-center glancing impact.
This resulted in the tilting of Earth's axis and the debris forming the moon.
Another thing I picked up somewhere is that when the Moon was first formed it was much closer to Earth and orbited much faster, imposing greater gravitational forces on Earth than what we experience now. The formation of the Moon acting as a rotational stabilizer for Earth.
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07-10-2014, 05:27 PM
RE: Why is the earth's axis tilted?
(07-10-2014 04:56 PM)smileXsmileXsmile Wrote:  
(07-10-2014 04:22 PM)cjlr Wrote:  The angular momentum imparted by collisions is not nearly enough to significantly alter the overall rotation of a planet.

Without going back to check for myself, it sounds like the quote you've pulled relates more to the eccentricity of the Earth's orbit, and not its axial tilt (it's spin motion and it's orbital motion being, for many purposes, essentially decoupled).

eccentricity in two dimensions wouldn't be a factor, but the slight angle of that eccentricity, in the third dimension might. All three planets must have their own somewhat angled eccentric orbit in the third dimension. There's also the factor of where Jupiter, Earth, and Venus lie on the z-axis.

But then again, isn't the earth's 23% tilt too extreme for venus, earth, and jupiter being "pretty much" being on the same (3 dimensional) plane? It might not be I don't know.


I'm dumbfounded. Can you, or anyone explain?

I suggest you consider all the planets.

Mercury's axis tilt is 0°.
Venus' axis tilt is 177.4° (or 2.60, depending on "north pole" definition).
Earth's axis tilt is 23.5°.
Mars' axis tilt is 25.2°.
Jupiter's axis tilt is 3.1°.
Saturn's axis tilt is 25.3°.
Uranus' axis tilt is 97.8°.
Neptune's axis tilt is 28.8°.

Dwarf planet Pluto's axis tilt is 122.5°.

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07-10-2014, 06:42 PM (This post was last modified: 07-10-2014 06:56 PM by smileXsmileXsmile.)
RE: Why is the earth's axis tilted?
I'm thinking it must have been impact theory because all of the planets are on the same 3 dimensional plane. It could've been impact theory during formation or impact theory after formation, but in my mind it would have to be impact theory. If axis tilt was based on gravity all of the planets would have a close to zero degree tilt from the start. I'm thinking Uranus got hit by a comet or something ...even though its gas ..idk.

The impact theory would be further plausible, because as we know, when a solar system forms, the cloud of debris gets flattens into a rotating disk via the nature of gravity, thus because of this flattened disk of the debris, i the maximum tilt wasn't able to achieve over 26° because all of the impacts were coming from within the rotating flattened disk of debris. I hope that made since.

wow so the show cosmos is wrong? Agree/Disagree?

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07-10-2014, 06:47 PM
RE: Why is the earth's axis tilted?
(07-10-2014 06:42 PM)smileXsmileXsmile Wrote:  I'm thinking it must have been impact theory because all of the planets are on the same 3 dimensional plane. It could've been impact theory during formation or after, but in my mind it would have to be impact theory. If axis tilt was based on gravity all of the planets would have a close to zero degree tilt, or saturn's 25.3° tilt, or mars' 25.2° tilt. Ur

wow so the show cosmos is wrong? Agree/Disagree?

I doubt the show was 'wrong'. There are competing theories.

Every planet has different orbital dynamics - each has a unique location and set of neighbors.

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