Mercury and Venus Lecture Notes

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.

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.