Mercury

Definition

Mercury is the smallest and innermost planet in the Solar System, orbiting the Sun. It is a terrestrial planet, meaning it has a solid surface, and is the closest planet to the Sun.

5 Must Know Facts For Your Next Test

1. Mercury has the most elliptical orbit of all the planets in the Solar System, with an orbital eccentricity of 0.206.
2. Mercury's orbital period around the Sun is approximately 88 Earth days, the shortest of all the planets.
3. The planet's small size, high density, and lack of a significant atmosphere contribute to its extreme temperature variations, ranging from $\approx$ 800 K (527 °C; 980 °F) at its hottest point to $\approx$ 100 K (-173 °C; -280 °F) at its coldest.
4. Mercury's rotational period is synchronous with its orbital period, meaning it rotates exactly three times for every two orbits around the Sun.
5. The planet's small size and high density suggest that it has a large, iron-rich core, which generates a weak magnetic field about 1% as strong as Earth's.

Review Questions

• Explain how Mercury's orbital eccentricity and synchronous rotation affect the planet's temperature variations.
  • Mercury's highly elliptical orbit, with an eccentricity of 0.206, causes significant variations in its distance from the Sun throughout its orbital period. This, combined with its synchronous rotation, where the planet rotates exactly three times for every two orbits around the Sun, results in extreme temperature fluctuations on the surface. During perihelion, when Mercury is closest to the Sun, the surface can reach temperatures of around 800 K (527 °C; 980 °F), while at aphelion, when the planet is farthest from the Sun, the temperature can drop to around 100 K (-173 °C; -280 °F). These dramatic temperature changes are a direct consequence of Mercury's unique orbital and rotational characteristics.
• Describe how Mercury's small size and high density contribute to the formation of its internal structure and magnetic field.
  • Mercury's small size, with a diameter of only 4,879 km, and its high density, which is similar to that of Earth, suggest that the planet has a large, iron-rich core that makes up a significant portion of its total volume. This core is believed to generate a weak magnetic field, about 1% as strong as Earth's, through a dynamo effect. The planet's small size and lack of a substantial atmosphere also contribute to the extreme temperature variations on its surface, as there is little to no insulation or heat retention. The combination of Mercury's internal structure and environmental factors shapes its unique characteristics as the smallest and closest planet to the Sun.
• Analyze how Kepler's Laws of Planetary Motion, specifically the relationships between a planet's orbital period, semi-major axis, and eccentricity, can be used to predict and understand the characteristics of Mercury's orbit around the Sun.
  • Kepler's Laws of Planetary Motion provide a framework for understanding the orbital dynamics of Mercury and other planets in the Solar System. The first law, which states that planets orbit the Sun in ellipses with the Sun at one focus, directly applies to Mercury's highly eccentric orbit. The second law, which describes the equal area swept out by a planet's radius vector in equal times, helps explain the variations in Mercury's orbital speed as it moves closer to and farther from the Sun. The third law, which relates a planet's orbital period to its semi-major axis, can be used to calculate Mercury's orbital period of approximately 88 Earth days, the shortest of all the planets. By applying these fundamental principles of celestial mechanics, we can accurately predict and analyze the unique orbital characteristics of Mercury, the smallest and innermost planet in our Solar System.

Related terms

Perihelion: The point in a planet's orbit when it is closest to the Sun.

Aphelion: The point in a planet's orbit when it is farthest from the Sun.

Orbital Eccentricity: A measure of how elliptical or non-circular a planet's orbit is around the Sun.