Why Has Mercury Become Locked into a 3-To-2 Spin Orbit

question 200

Multiple Choice

Why has Mercury become locked into a 3-to-2 spin orbit coupling instead of a 1-to-1 coupling like the Moon around Earth?

• A) Mercury feels a stronger gravitational pull from the more massive Sun than the Moon does from Earth, so its rotation became locked on the Sun before it had slowed enough for a 1-to-1 lock.
• B) Mercury's orbit is very eccentric, so its orbital speed varies while its rotation rate remains constant, preventing a 1-to-1 lock.
• C) Mercury's rotation rate is still slowing down, and the apparent 3-to-2 lock is actually just coincidence.
• D) Mercury's orbit is highly inclined (tipped up at an angle to the orbits of the other planets), so the Sun sometimes pulls more on Mercury's north pole and sometimes more on its south pole.

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Definitions:

Difference Threshold

The minimum difference in stimulation that a person can detect 50% of the time, also known as the "just noticeable difference" (JND).

Energy

The capacity to do work or the power derived from the utilization of physical or chemical resources.

Original Stimulus

The initial event or object that triggers a sensory or psychological response.

Weber Fraction

A principle stating that the smallest change in a stimulus that can be detected is a constant proportion of the starting level of that stimulus.