Why Do Some Planets Rotate In Different Directions?

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At this point in life, we should all know the basics of our solar system, namely that there are nine eight planets that rotate about themselves on an axis at a particular angle, in addition to revolving around the sun in an orbit.

However, did you know that within our solar system, there are a few outlying planets that do not spin in the same direction as Earth and most other planets?

Which planets rotate in a different direction?

The two anomalies in question are Venus and Uranus. These planets rotate in the clockwise or retrograde direction while all the other planets rotate in the counter-clockwise motion.

A single day on Venus is much longer than one on the Earth. It takes 243 Earth days to complete its rotation, but it only takes 224.7 days to complete each orbit. Yes, that means that a day on Venus is longer than a year!

Which way does the Earth rotate?

The Earth rotates in the counter-clockwise direction like the majority of the planets in our Solar System. Its tilt is 23 degrees in the prograde direction.

Let’s understand what prograde and retrograde mean.

source: www.reddit.com

source: www.reddit.com

What is the Prograde and Retrograde rotation?

Prograde rotation indicates that the motion is in the same direction as the Sun’s rotation. Retrograde rotation is in the opposite direction. Most planets in our solar system, including Earth, rotate counter-clockwise or prograde direction, but Venus and Uranus are said to have a retrograde or clockwise rotation around their axes. The tilt angle of a planet is measured relative to the orbital plane of the planet, and most planets’ axes form an almost perpendicular angle to the orbital plane.

However, along with being retrograde, Uranus also has a tilt of 97.7 degrees, which makes its axis almost horizontal to the orbital plane. Although scientists and astronomers do not have a specific or proven reason for these anomalies, they have proposed some hypothetical explanations.

What could be the explanation?

One of the most popular explanations for these anomalies is that at some point in history, Venus and Uranus both spun counter-clockwise, just like the other planets. However, in the events that followed the development of planets, Venus was somehow flipped 180 degrees on its axis. So ideally, Venus is still spinning in the prograde direction, but since it was somehow knocked upside down, it appears to be spinning in a clockwise direction.

The next question that naturally arises from this theory is: what made the planet flip? God’s hand! His divine plan? No, not really!

The evidence of huge craters on the surfaces of these planets has hinted at the possibility that a huge mass collided with the planets in their formative days. For example, if you even slightly nudge a spinning top it will definitely wobble. The top won’t stop spinning entirely but it will tilt. Similar logic may apply in case of Venus and Uranus’ spin angle. Scientists hypothesized this by guessing from Earth’s early collision that led to the formation of the moon; in this case, however, the collision flipped the planets over! Another explanation refers to the Sun’s gravitational pull, which caused strong atmospheric tides, eventually resulting in the flipped-over axes of these planets.

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A third explanation for Venus’ inverted axis is related to the interaction between the friction forces of its core and mantle, or those same forces between its atmosphere and mantle. A planet has to conserve its total angular momentum, which is directly related to its net spin axis. However, the net spin axis of a planet is a combination of the spin axis of its core, the spin axis of its mantle and the spin axis of its atmosphere.

Because Venus’ core is liquid and due to the planet’s thick atmosphere, it is possible that frictional forces changed the angular momentum between the core and the mantle, or the atmosphere and mantle, thus causing the flip. It seems like a solution that warring members of a family employed for peaceful co-existence.

As for Uranus, it is believed that the planet was hit by multiple bodies, roughly the size of earth, that led to its unique flip and clockwise rotation.

If you catch yourself wishing the days were longer or the sun rose from the west…you know to which planet you need to shift your base!

References

  1. Uranus -NASA
  2. Venus – NASA
  3. California Instirute of Technology
  4. The National Radio Astronomy Observatory
The short URL of the present article is: http://sciabc.us/oVH1d
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About the Author:

Rujuta has a MA in Counseling Psychology and MSc in Cognitive Science. She is currently pursuing a PhD in Cognitive Science from IIT Kanpur in India. Her primary area of interest being human memory and learning, she is also interested in the neuroscience of cognitive processes. She also identifies herself as a bibliophile and a harry potter fanatic.

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