Astronomy 1003: Crater Worlds - The Moon and Mercury

Astronomy 1003: Crater Worlds - The Moon and Mercury

Introduction

• Overview of Chapter Nine: Crater Worlds

  • Focus on the Moon and Mercury

  • Themes include:

  • General properties of the Moon

  • Lunar surface features

  • Impact craters

  • Origin of the Moon

  • Properties of Mercury

General Properties of the Moon

• Mass:

  • The moon has only ext{1/80} the mass of Earth.

• Surface Gravity:

  • Moon’s gravity is about ext{1/6} of that of Earth.

• Atmosphere:

  • Moon cannot retain an atmosphere due to low gravity.

• Impact on Historical Observation:

  • The Moon acts as a time capsule, preserving ancient solar system history due to its airless surface.

Escape Velocity

• Definition: Minimum speed to permanently escape another body's gravity.

• Escape Velocity of the Moon:

  • Approximately ext{2.4 km/s}.

• Earth’s Escape Velocity:

  • Approximately ext{11.2 km/s}.

Volatiles

• Definition of Volatiles:

  • Elements in compounds that evaporate at low temperatures (e.g., alcohol, water).

• Moon’s Composition:

  • Deficient in a variety of volatiles.

Comparative Properties of Moon and Mercury

• 
  

• Table 9.1 Summary
  

  Property	Moon	Mercury
  Mass	ext{1/80 Earth}	ext{1/20 Earth}
  Diameter	3,476 km	4,878 km
  Density	3.3 g/cm³	5.4 g/cm³
  Surface Gravity	ext{1/6 Earth}	0.38 Earth
  Escape Velocity	2.4 km/s	4.3 km/s
  Rotation Period	27.3 days	58.6 days
  Surface Area % of Earth	27%	38%
  Apollo Program and Lunar Exploration

  • Apollo Missions

    • Nine piloted missions from 1968 to 1972.

    • First manned Moon landing on July 20, 1969 (Apollo 11, Neil Armstrong).

  • Contribution to Lunar Geology:

    • Collecting nearly ext{400 kg} of lunar samples for analysis.

    • Deployment of Apollo Lunar Surface Experiments Package (ALSEP).

  Significant Apollo Missions

  • Apollo 8: First crewed mission to orbit the Moon; historic photos taken.

  • Apollo 10: Lunar module test flight without landing.

  • Apollo 13: Known for in-flight emergency and drama.

  • Apollo 15: First use of a lunar rover for exploration.

  • Apollo 16 & 17: Focused on geological discoveries, significant sample collections.

  Composition and Structure of the Moon

  • Average Density:

    • 3.3 g/cm³, primarily composed of silicate rocks.

  • Absence of large metal core confirmed by Apollo seismic data.

  • Previous studies indicated water and volatiles are scarce, but some water found in samples.

  • Lunar Ice Discovery:

    • Impact from the L Cross mission found significant water ice in polar craters, useful for future exploration.

  The Lunar Surface

  • Visible Features: Impact craters and dark basalt plains (Mare).

  • Geological Processes: Influence of impacts and volcanic activity.

  Lunar Highlands and Maria

  • Highlands:

    • Consist of low-density rock, heavily cratered, oldest surface.

  • Maria:

    • Younger, less cratered volcanic plains, rich in basalt composition.

  • Volcanic Activity Ceased: Major volcanism ended around 3.3 billion years ago.

  Impact Cratering

  -Crater Formation Process:

  • Craters differ from volcanic craters in origin and structure.

  • Formation includes shock waves, vaporization, and ejecta blanket.

    • Cratering Rates:

  • Estimations of crater formation suggest a constant rotation of impacts.

  Estimating Lunar Age

  • Crater Count Method:

    • A 1 km crater forms every ext{200,000} years.

  • Aging of Moon’s surface confirmed by radiometric data showing ages between ext{3.3 to 4.4 billion years}.

  Origin of the Moon

  • Theories Explored:

    • Fission, Sister, and Capture hypothesis.

  • Current Leading Theory: Giant Impact Hypothesis.

    • Suggests Earth was struck by a Mars-sized body.

    • Ejected material formed the Moon's structure.

  Introduction to Mercury

  • Characteristics:

    • Mercury is an airless, cratered terrestrial planet.

    • Diameter: 4,878 km, with a high density of 5.4 g/cm³.

  • Shortest orbital period in the solar system (88 days).

  Mercury’s Composition

  • Internal Structure:

    • Large iron core (approximately 60% of mass), rocky crust (700 km thick).

  • Orbital Characteristics: Semi-major axis ext{50,000,000 km (0.39 AU)} with eccentric orbit.

  Exploration of Mercury

  • First close-up images from Mariner 10 in 1974, further detailed by MESSENGER.

  • Surface features including craters and evidence of past volcanic activity.

  Conclusion

  • Insights into the Moon and Mercury enhance understanding of solar system history and geological processes.

  • Importance of lunar and Mercurial studies for future missions, highlighted by NASA’s Artemis program aiming for lunar exploration.