Earth's tilt

[Zeta Reticulum]

I was taught that Earth's tilt was due to a freak accident..... as rare as rare can be.

So does that mean that there would be few if any planets with a tilt... therefore, the majority of planets would not have seasons?

[Mikko-kun]

Seasons are because of tilt so yeah. Didn't Uranus have vertical tilt, very uncommon in our solar system?

[sepulchrave]

I was taught that Earth's tilt was due to a freak accident..... as rare as rare can be.

So does that mean that there would be few if any planets with a tilt... therefore, the majority of planets would not have seasons?

I don't think so. See the wiki on axial tilt; there are many things that can cause it.

I think perhaps a single planet closely orbiting a star would be tidally locked and unlikely to have any axial tilt, but any planet in a multi-body solar systems and/or possessing moons would have some axial tilt; the odds that all of these other objects would be perfectly in-plane with the planet and not exert any gravitational torque I think would be extremely slim.

[Waspie_Dwarf]

I was taught that Earth's tilt was due to a freak accident..... as rare as rare can be.

So does that mean that there would be few if any planets with a tilt... therefore, the majority of planets would not have seasons?

Whilst we can not detect the axial tilt (known to astronomers as "obliquity" yet, looking at the other planets in the solar system tells us that there is nothing rare about the Earth's tilt.

The values for the planets (and the dwarf planets Ceres and Pluto) are:

Mercury - 0^o

Venus - 2.64^o (or 177.36^o)

Earth - 23.45^o

Mars - 25.29^o

Ceres - >3^o

Jupiter - 3.13^o

Saturn - 26.73^o

Uranus - 82.23^o (or 97.77^o)

Neptune - 28.33^o

Pluto - 60.41^o (or 122.53^o)

You will notice that for Venus, Uranus and Pluto I have quoted 2 figures. The first is the International Astronomical Union figure and the second is the NASA figure. The big difference is because there are two ways of defining which is the North pole of the planet. The IAU defines the North pole as the one above the plane of the ecliptic. Under IAU designations Venus, Uranus and Pluto revolve in a retrograde (opposite to normal) way.

NASA and some other organisations define the North pole differently, they effectively say that all planets rotate the same way but Venus, Uranus and Pluto have been flipped so that their North poles point below the plane of the ecliptic. Both systems are equally valid.

I would think that the 0^o value for Mercury is almost certainly due to the tidal locking that sepulchrave mentioned.

Is it possible that you misunderstood what you were told?

As can be seen from the figures above there is nothing unusual about the Earth's obliquity. However these values are not constant, obliquity can change. There are those that theorise that Earth, having such a large moon, is saved from the wilder excesses of obliquity change. The Moon stabilises Earth and reduces the influence of such changes. It is further hypothesised by some that this helped make the Earth are more hospitable place for the development of life.

Is it possible that this "accident" of having a large Moon and a stable axial tilt is the "freak accident" that you were referring too?

[Mikko-kun]

If you're big, then there's all the more chance something hits you. I'd imagine even smaller hits can have effect to our rotation, even if a very very miniscule one. Like drops on a river. Dont know if there's anything that stabilizes that tilt over time, something like Sun's gravity.

[Waspie_Dwarf]

I'd imagine even smaller hits can have effect to our rotation, even if a very very miniscule one.

If this is correct explain the obliquity of Uranus.

[Zeta Reticulum]

Thanks for the clarification Waspie. Very interesting.

[Mikko-kun]

If this is correct explain the obliquity of Uranus.

Just my guess smaller particles can have an impact. The problem with relativity is, where do you draw the line in what size/mass/speed object colliding has an impact on rotation. Different objects having also different relative rotation speeds adds up to the variety of them. Perhaps Uranus at least once was under a way of some very big object that hit it from vertical position to a right spot, or a lot of smaller objects, even an area like the asteroid belt. Just guesses but I dont know how else to explain it's rotation angle.

What about the possible negating effects? In addition to impacts having a lesser effect due to bigger size & mass of Uranus. Maybe the nature of time, if past has a sort of lag that drags behind and tries to pull you back, like time-dimension's gravity. Or maybe there's a constant in the change-energy, universal energy that drives everything towards a chance. Perhaps if there was too much change-energy at one monent, the surroundings would try to stabilise it to reach the constant that's always there by making themselves be more still. That seems more plausible than time-lag to me, might negate the small impacts too. If you apply any rule like that to the impact event and assume that kind of rule makes the impact energy gradually diminish, more and more before it can reach all of the object, that can create a limit to what size of objects have an impact on rotation. Because if there was no balancing-out rule, wouldn't the rotations undergo more rapid changes?