Insights on Mercury: The Elusive Planet

Sep 25, 2024

Lecture Notes: Mercury

Overview

  • Mercury is the closest planet to the Sun.
  • Known for extreme temperature variations.
  • One of the seven naked-eye solar system objects.
  • Associated with the Roman messenger god, known for its speed.

Historical Observations

  • Mercury's motion observed by Giovanni Zupi in 1639.
  • Exhibits phases like the Moon, proving it orbits the Sun.
  • Supports heliocentrism.

Orbit and Rotation

  • Average distance from the Sun: 58 million km (1/3 of Earth's distance from the Sun).
  • Rapid orbital movement due to proximity to the Sun.
  • Completes an orbit in 88 Earth days.
  • Phases observed due to relative positions to Earth and Sun.
  • Elliptical orbit: closest at 46 million km and farthest at 70 million km.

Spin-Orbit Resonance

  • Unique 2:3 spin-orbit resonance.
  • One day on Mercury lasts 59 Earth days.
  • Tidal forces once slowed Mercury's rotation.
  • At perihelion, one side faces the Sun and 1.5 spins later, the opposite side faces the Sun.
  • This results in a peculiar day length of 176 Earth days.

Surface and Atmosphere

  • Small size: 4900 km in diameter (1/3 of Earth's width).
  • Bright due to proximity to Sun but hard to observe due to horizon position.
  • Mapped by Mariner 10 and MESSENGER probes.
  • Surface is rocky with extensive cratering.
  • Notable features include Caloris Basin and "rupes" or compression folds.

Magnetic Field and Core

  • Has a magnetic field despite slow rotation.
  • Dense with a large iron core, possibly from a past grazing impact.
  • Core may reach Âľ of the way to the surface.

Atmospheric Conditions

  • Minimal atmosphere with traces due to solar wind and impacts.
  • Long comet-like tail made of elements like sodium and magnesium.

Impact Events

  • Craters formed by high-velocity impacts due to Mercury's fast orbit.

Ice on Mercury

  • Water ice exists in deep craters at the poles.
  • Ice located in "cold traps" where sunlight never reaches.
  • Likely sourced from comet/asteroid impacts.

Interesting Facts

  • Ice on a planet with extremely high surface temperatures.
  • Mercury's environmental conditions demonstrate nature's complexity.

Acknowledgements

  • Lecture by Phil Plait with contributions from Blake de Pastino and Dr. Michelle Thaller.

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