Mercury and Venus Lecture Notes

Mercury and Venus Overview

• Learn about key characteristics of Mercury and Venus.
• Explore their exploration history.

The Inner Planets

• Sizes Relative to Earth:
  • Mercury: 0.38 Rₑ (Earth radii)
  • Venus: 0.95 Rₑ

Mercury

• General Characteristics:

  • Closest planet to the Sun.
  • No moons.
  • Lacks significant atmosphere.
  • Smallest planet in the solar system, smaller than moons Ganymede and Titan but more massive.
  • Has a global magnetic field (1% strength compared to Earth).

• Temperature Variations:

  • Day temperature: 427°C (800°F) at equator.
  • Night temperature: -143°C (-280°F) at equator.
  • Note: Extreme temperature range due to proximity to the Sun and lack of atmosphere.

• Orbital and Rotational Dynamics:

  • Highest eccentricity in orbit of all planets.
  • Orbital period: 88 days.
  • Rotational period: 58.6 days (locked in a 3:2 spin-orbital resonance).
  • This means: 3 rotations for every 2 orbits.

• Historical Observations:

  • Mariner 10: First satellite to visit multiple planets (1973-1975).
  • MESSENGER: Explored Mercury (2004-2015).

• Surface Features:

  • Unique stress marks (hundreds of kilometers long and several kilometers high).
  • Caloris Basin: unusual terrain observed on the opposite side of Mercury.

Venus

• General Characteristics:

  • Second planet from the Sun.
  • No moons.
  • Slightly smaller than Earth.
  • Hottest planet in the solar system: Surface temperature is 460°C (860°F).
  • Lacks a magnetic field unlike Earth and Mercury.

• Day and Year Duration:

  • Venus takes 243 Earth days to rotate but only takes 225 Earth days to orbit the Sun, making a "day" longer than a "year."
  • Sun rises in the west and sets in the east.

• Atmosphere:

  • Surface atmospheric pressure: 90 times that of Earth's (equivalent to being half a mile underwater).
  • Composition: Mostly CO₂ with sulfuric acid rain clouds.

• Geological Features:

  • Volcanism and Outgassing:
  • Initial atmosphere created by volcanic outgassing (mainly CO₂ and sulfur).
  • Active volcanism indicated by spikes in atmospheric sulfur content; over 85,000 volcanoes present across the surface.
  • Surface Conditions:
  • Few impact craters due to continuous volcanic resurfacing.
  • Little erosion from water and low surface wind.

• Exploration History:

  • Multiple missions including the Soviet Venera missions, USA's Mariner 10 and Magellan orbiters, ESA’s Venus Express, and JAXA’s Akatsuki probe.

• Evidence of Past Water:

  • Deuterium levels significantly higher than on Earth suggest a lost ocean on Venus.

Preparation for Next Class

• Review textbook sections 9.1, 9.2, 9.4, 10.2, and 10.4.
• Complete HW set 7 (due TOMORROW) and start HW set 8.