Question

the planet mercury has a revolution period of 88 days. why does earth have a longer revolution period?
mercury has a thicker atmosphere than earth.
earth has a greater gravitational force than mercury
earth takes longer to rotate on its axis than mercury
mercury has a shorter revolution period due to it being closer to the sun.

Explanation:

• Atmosphere thickness: The thickness of a planet's atmosphere has no direct relation to its revolution period.
• Gravitational force: While Earth has a greater gravitational force than Mercury, this is not the reason for the difference in revolution periods.
• Axial rotation: Axial rotation (which determines a planet's day - night cycle) is different from revolution (which determines a planet's year).
• Distance from the Sun: According to Kepler's third law of planetary motion, the square of the orbital period ($T$) of a planet is proportional to the cube of the semi - major axis ($a$) of its orbit ($T^{2}\propto a^{3}$). Mercury is closer to the Sun (shorter semi - major axis of its orbit around the Sun) than Earth. So, Mercury has a shorter revolution period.

Answer:

Mercury has a shorter revolution period due to it being closer to the Sun.