Answer to Question 1
Mercury is tidally coupled to the Sun but in a different way than the Moon is coupled to Earth. Mercury rotates not once per orbit but 1.5 times per orbit. That is, its period of rotation is exactly 2/3 of its orbital period. If you flew to Mercury and landed your spaceship in the middle of the day side, the Sun would be high overhead, and it would be noon. Your clock would show almost 44 Earth days passing before the Sun set in the west, and a total of 88 Earth days would pass before the Sun reached the midnight position. In those 88 Earth days, Mercury would have completed one orbit around the Sun - a full day on Mercury is two Mercury years long
The complex tidal coupling between the rotation and revolution of Mercury is an important illustration of the power of tides. Just as the tides in the EarthMoon system have slowed the Moon's rotation and locked it to Earth, so have the SunMercury tides slowed the rotation of Mercury and coupled its rotation to its revolution. Model calculations indicate that, because of Mercury's moderately eccentric orbit, the 3:2 resonance is more stable than the 1:1 resonance that is exhibited by Earth's Moon.
Like its rotation, Mercury's orbital motion is complex. Mercury's elliptical orbit precesses (twists) faster than can be explained by Newton's laws, but at precisely the rate predicted by Einstein's theory of general relativity. The orbital motion of Mercury is taken as strong confirmation of the curvature of space-time as predicted by general relativity.
Answer to Question 2
planetary
Mercury’s Orbit Explained by General Relativity
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Zone for Habitable Planets
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A portable mercury sphygmomanometer. Mercury versions are being phased out of medical offices and ...
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