True polar wander
True polar wander is a solid-body rotation of a planet or moon with respect to its spin axis, causing the geographic locations of the
If the body is near the steady state but with the angular momentum not exactly lined up with the largest moment of inertia axis, the pole position will oscillate. Weather and water movements can also induce small changes. These subjects are covered in the article Polar motion.
Description in the context of Earth
The mass distribution of the
This situation is like a
Such a reorientation changes the
Examples
Cases of true polar wander have occurred several times in the course of the Earth's history.
Uranus' extreme inclination with respect to the ecliptic is not an instance of true polar wander (a shift of the body relative to its rotational axis), but instead a large shift of the rotational axis itself. This axis shift is believed to be the result of a catastrophic series of impacts that occurred billions of years ago.[5]
Distinctions and delimitations
Polar wander should not be confused with precession, which is where the axis of rotation moves, in other words the North Pole points toward a different star. There are also smaller and faster variations in the axis of rotation going under the term nutation. Precession is caused by the gravitational attraction of the Moon and Sun, and occurs all the time and at a much faster rate than polar wander. It does not result in changes of latitude.
True polar wander has to be distinguished from continental drift, which is where different parts of the Earth's crust move in different directions because of circulation in the mantle.
The effect should further not be confused with the effect known as geomagnetic reversal that describes the repeated proven reversal of the magnetic field of the Earth.
Tectonic plate reconstructions
Paleomagnetism is used to create tectonic plate reconstructions by finding the paleolatitude of a particular site. This paleolatitude is affected both by true polar wander and by plate tectonics. To reconstruct plate tectonic histories, geologists must obtain a number of dated paleomagnetic samples. Because true polar wander is a global phenomenon but tectonic motions are specific to each plate, multiple dates allow them to separate the tectonic and true polar wander signals.
See also
- Apparent polar wander
- Axial tilt
- Cataclysmic pole shift hypothesis (includes discussion of various historical conjectures involving rapid shift of the poles)
- Polar motion
- True polar wander on Mars
References
- S2CID 4344501.
- PMID 34131126.
- S2CID 210309183.
- ^ Ron Cowen (June 7, 2008). "A Shifty Moon". Science News. 173 (18). Archived from the original on November 4, 2011. Retrieved May 29, 2008.
- ^ Kate Taylor (October 11, 2011). "Tipped Over By Several Collisions". TG Daily. Archived from the original on January 26, 2012. Retrieved February 29, 2012.