How our Moon and Sun may affect Earth's equatorial bulge

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Discussion Overview

The discussion centers on the factors influencing Earth's equatorial bulge, particularly the roles of the Moon's tidal forces and the comparative characteristics of Mars. Participants explore the relationship between planetary rotation, viscoelastic properties, and the resulting equatorial bulge percentages.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that Earth's equatorial bulge is influenced by the Moon's tidal forces, questioning what the bulge percentage would be without this influence.
  • Another participant argues that the equatorial bulge is significantly larger than tidal effects and attributes the differences between Earth and Mars to their sizes and gravitational accelerations.
  • A participant seeks clarification on the specific measurements of the equatorial bulge percentages (6% for Mars and 3% for Earth), asking whether these refer to the equator to North-South pole diameter or another metric.
  • One participant reiterates that the equatorial bulge of Earth aligns more closely with theoretical predictions, while Mars's bulge appears anomalous, suggesting that Mars's characteristics require further explanation.

Areas of Agreement / Disagreement

Participants express differing views on the influence of the Moon on Earth's equatorial bulge, with some asserting its impact while others contest this notion. The discussion remains unresolved regarding the precise reasons for the differences in equatorial bulge between Earth and Mars.

Contextual Notes

Participants have not fully defined the terms used in their comparisons, and there are unresolved assumptions regarding the effects of planetary size and gravitational acceleration on equatorial bulge measurements.

lunatectonics
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the equatorial bulge of a planet is affected by the planet's rotation and viscoelasticity of the sphere. Venus's rotation period is 244 days with an equatorial bulge of 0%. Earth's and Mars's rotations are almost identical at 1 day and 1.03 days, yet Mars's equatorial bulge is 6% vs Earth's 3%. Mars has has a colder mantle with viscosity estimated 10 - 100 times earth's viscosity.

Given that Earth's shell is more mobile and responsive to deformation , what would be Earth's equatorial bulge % if the Moon's tidal forces were not squeezing it ? the sun being constant with both Mars and Earth.
 
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It sounds like you're saying you think the moon impacts the Earth's equatorial bulge, decreasing its size vs Mars'. The equatorial bulge is much, much larger than the tides (and exists around the entire equator), so it doesn't explain the difference. The difference is probably explained by the difference in size between the planets. A smaller planet has a smaller tangential velocity but a much smaller gravitational acceleration at the surface.
 
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lunatectonics said:
Mars's equatorial bulge is 6% vs Earth's 3%
To what are the 6% and 3% comparison referring.
Equator to North-South pole diameter, or something else.
 
russ_watters said:
It sounds like you're saying you think the moon impacts the Earth's equatorial bulge, decreasing its size vs Mars'. The equatorial bulge is much, much larger than the tides (and exists around the entire equator), so it doesn't explain the difference. The difference is probably explained by the difference in size between the planets. A smaller planet has a smaller tangential velocity but a much smaller gravitational acceleration at the surface.
The earth's Equator to North-South pole diameter bulge is more close to theoretical, and Mars is out is whack.
If anything, Mars needs explaining.
 

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