Exam 3

🌕 The Moon

Atmosphere

• The Moon has no atmosphere, which:

  • Prevents weathering or erosion

  • Preserves surface features like craters

Craters

• Sharp-edged craters = younger

• Rounded edges = older, eroded by micrometeorites

• Ejecta blankets (material thrown out during impact):

  • Younger craters have lighter-colored ejecta

• Far side vs. Near side:

  • Far side has fewer maria

  • Earth’s gravity caused thinner crust on the near side → easier for magma to reach surface after impacts

Surface Features

• Regolith = layer of fine dust and broken rock

  • Formed by constant micrometeorite impacts over billions of years

Mineralogy

• Highlands are composed of anorthosite (rich in plagioclase)

  • Similar rocks found in Earth’s Adirondack Mountains

Formation

• Formed from a giant impact with Earth (~4.5 billion years ago)

  • Impact with a Mars-sized body, Theia

Volcanism

• Volcanic activity occurred billions of years ago

  • No current or recent volcanic activity

☿ Mercury

Atmosphere

• Mercury has no true atmosphere

  • Only a thin exosphere made of:

    • Helium, sodium, oxygen, potassium, hydrogen

• Solar wind easily strips away gases due to low gravity

Temperature Extremes

• Dayside: ~800°F (427°C)

• Nightside: ~-297°F (-183°C)

• Most extreme temperature swing in the solar system

Orbit and Rotation

• Revolution: 88 Earth days

• Rotation: 59 Earth days

• 3:2 spin-orbit resonance:

  • Mercury rotates 3 times for every 2 orbits

  • Tidal locking causes same side to face the Sun at perihelion

Surface Features

• Resembles the Moon: heavily cratered, ancient lava plains

• Major impact: Caloris Basin

  • Caused by 60-mile-wide iron meteorite

  • Created Weird Terrain on the opposite side

• Scarps (cliffs):

  • Caused by cooling and shrinking of Mercury's interior

Interior & Composition

• Extremely high density (5.4 g/cm³)

  • Indicates a large iron core

• May have shrunk due to cooling of molten core

• Weak magnetic field due to molten core

Missions

• Mariner 10 (1974): first flyby, mapped ~half the surface

• MESSENGER (2011): orbited and studied geology

• BepiColombo (2025): will study magnetosphere, planetary shrinking, and water ice at poles

♀ Venus

Atmosphere

• Extremely thick atmosphere, 96% carbon dioxide

• Atmospheric pressure = 92x Earth's

• Causes runaway greenhouse effect:

  • Traps heat → surface temperature ~850°F (462°C)

Rotation

• Rotates clockwise (retrograde) — opposite of most planets

• One day = 243 Earth days

• One year = 225 Earth days

Surface and Composition

• Basaltic surface (volcanic rock)

• Surface hidden under thick clouds

• Features:

  • Pancake domes, shield volcanoes, lava plains

  • Meandering rilles from past lava flows

  • Few craters: small meteoroids burn up in the atmosphere

Volcanism

• Likely resurfaced ~500 million years ago

• No plate tectonics

• Still unclear if volcanoes are currently active

Missions

• Mariner 2, Pioneer Venus, Venera landers, Magellan (1990–94 radar mapping)

• Future missions: DAVINCI and VERITAS

♂ Mars

Atmosphere

• Very thin (0.007 bar, ~1% of Earth's)

• 96% carbon dioxide

• Too cold for liquid water; only ice or gas forms

Seasons and Rotation

• Axis tilt = similar to Earth → has seasons

• Sol (day) = 24.6 Earth hours

• Year = 687 Earth days

Surface Features

• Olympus Mons: tallest volcano in solar system (3x Mt. Everest)

• Valles Marineris: largest canyon (3000 miles long, 7 miles deep)

• Tharsis Bulge: region of giant shield volcanoes

Water History

• Ancient water channels and deltas

• Sinus Meridiani evidence:

  • Jarosite (forms in water), “blueberries” (hematite spheres)

  • Cross-bedding, sulfur, and chlorine → signs of evaporated water

Climate Change

• Early Mars: had a magnetic field → protected atmosphere

• Field weakened → solar wind stripped atmosphere → greenhouse effect declined

• Surface water disappeared ~3 billion years ago

Current Weather

• CO₂ frost caps at poles (grow/shrink with seasons)

• Condensation flow moves gas from pole to pole

• Violent dust storms

• Pink skies, blue sunsets

Missions

• Viking, Pathfinder, Spirit & Opportunity

• Curiosity and Perseverance:

  • Explore geology, habitability, and search for signs of ancient life

✍ Essay Preparation: Why is Venus the way it is? Compare Venus to Earth

Key Points to Cover:

• Atmosphere:

  • Venus: thick CO₂, no water/life → heat trapped, runaway greenhouse effect

  • Earth: CO₂ cycle controlled by water, limestone, and life

• Volcanism:

  • Venus: surface reshaped by volcanic flows, no plate tectonics

  • Earth: dynamic volcanism with tectonic plates and water interactions

• Magnetic Field:

  • Venus: weak or nonexistent → no protection from solar wind

  • Earth: strong magnetic field from molten core

• Rotation & Pressure:

  • Venus: slow retrograde rotation, high surface pressure

  • Earth: fast prograde rotation, balanced atmosphere

Conclusion:

• Venus became inhospitable due to lack of life, water, and magnetic shielding

• Earth remained habitable through stabilizing feedback from the biosphere