# Did the Moon ever approximate a geosynchronous orbit above the early Earth?

Simulations suggest the early Moon formed about 20,000 to 30,000 km away from Earth which is less than the current geosynchronous orbit of 42,164 km. The Moon is now 384,000 km away from Earth. Does that mean the moon approximated a geosynchronous orbit for a time on its journey outward to its current orbit? I recognize because of the Earth's tilt of 6.7 degrees the Moon does not orbit around the Earth's equator and therefore a geostationary orbit wasn't possible.

If the early Earth was a water world covered almost entirely with water at the time it formed, what would happen when the Moon approached geosynchronous orbit and applied its much more amplified gravitational force upon the Earth? Would there be tidal bulges of water at both ends exposing land at the polar regions or would the water eventually make its way toward the Moon side possibly exposing or making a bulge of land at the opposite end of the Earth?

Maybe. The period of a 20,000 km orbit is about 7h 50m. Wikipedia says:

[The Earth] would have experienced a day some five hours long after the impact, and the Earth's equator and the Moon's orbit would have become coplanar.

In the present era, the Moon's orbital plane is tilted by 5.145° to the ecliptic (the Earth's orbital plane); the obliquity of the ecliptic (relative to Earth's equatorial plane) is about 23.4°. However, as Wikipedia says:

The Moon's orbit around Earth has many irregularities (perturbations), the study of which (lunar theory) has a long history.

The post-impact Earth was very hot, and had a magma ocean for a while. However, it soon had liquid water again because the high atmospheric pressure pushed the boiling point of water way up.

From Wikipedia:

[From the Theia impact] a fair fraction of material should have been vaporized by this impact, creating a rock vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a heavy $$\mathrm{CO_2}$$ atmosphere with hydrogen and water vapor. Liquid water oceans existed despite the surface temperature of 230 °C (446 °F) because at an atmospheric pressure of above 27 atmospheres, caused by the heavy $$\mathrm{CO_2}$$ atmosphere, water is still liquid. As cooling continued, subduction and dissolving in ocean water removed most $$\mathrm{CO_2}$$ from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared.

It is difficult to estimate the effects of the interaction between the early Moon and that primordial ocean.

• The perturbations mentioned in Wikipedia seem to relate to the current situation and do not affect the orbital period. – Keith McClary Apr 13 at 17:32
• @Keith Correct. That section talks about the Moon's orbit in the current era, and points out that the orbital plane has shifted since the Moon's formation. Also, that the Moon's motion is rather complicated, even today. Eg, the orbital plane precesses with a fairly short period. Tidal effects have reduced the eccentricity, and reduced the various precessions to a degree, but not completely, because there are still forces maintaining the perturbations, because the Moon is so large relative to the Earth, and the influence of the Sun has a big effect. Even Jupiter has a noticeable influence. – PM 2Ring Apr 13 at 19:51