Chapter 6

Quote by Douglas Adams: "In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move."

Homework 8 due: Thursday, October 2
Homework 9 due: Thursday, October 9
Important Dates:
- October 10: Last date to withdraw with WP
- Mission Proposal Rethink due: October 14
- Homework 10 due: Thursday, October 16
Important Note: "We have your satellite if you want it back send 20 billion in Martian money. No funny business or you will never see it again." - Graffiti at NASA's Jet Propulsion Labs.

Characteristics of Solar System:
- Planets exhibit distinct patterns in composition and motion.
- These patterns transcend mere numerical data and nomenclature, providing more profound insights.

Diagram illustrating the inner solar system featuring:
- Venus, Sun, Mercury, Earth, Mars: Close-up of planets with exaggerated sizes compared to their orbits.
- Clear representation of overall solar system structure, emphasizing scale differences among elements.

Orbit Characteristics:
- Eight major planets with nearly circular orbits
- Pluto classified due to its smaller size and elliptical orbit
- All planets orbit in the same direction (counter-clockwise) and maintain a shared plane (the ecliptic).

Definitions:
- SIZE: Refers to the physical volume of a planet.
- MASS: The total amount of matter in an object.
- DENSITY: This is calculated as $\text{DENSITY} = \frac{\text{MASS}}{\text{VOLUME}}$ . Density is influenced by the composition of matter within a planet, not merely its size.

Visual representations comparing planetary sizes and distances.
Emphasizes how small planets are in relation to the vast distances between them.

Importance of Comparative Studies:
- Analyzing planets together uncovers patterns that enhance our understanding of Earth.
- Focus on processes that are common across multiple worlds, rather than unique facts regarding each.

Composition and Characteristics:
- Contains over 99.9% of the solar system's total mass.
- Mainly made of hydrogen and helium gas (in plasma form).
- Generates energy by converting approximately 4 million tons of mass into energy each second.

Mercury:
- Composition: Metal and rock, large iron core.
- Surface: Highly cratered, long, steep cliffs.
- Temperature variation: 425°C during the day; -170°C at night.
Venus:
- Nearly the same size as Earth; surface obscured by clouds.
- Experiences extreme greenhouse effect leading to temperatures of 470°C, constant day and night.
Earth:
- Unique among planets for its significant liquid water presence.
- Earth-Moon system shows a remarkably large moon compared to Earth itself.
Mars:
- Surface features resembling Earth; notable for massive volcanoes and canyons.
- Historical evidence of water flow may suggest past life.

Asteroids:
- Primarily located between Mars and Jupiter; remnants from solar system formation.
- Contain some of the oldest rocks, offering insight into solar system origins.
Jupiter:
- Surrounded by a massive atmosphere, primarily hydrogen and helium, with no solid surface.
- Mass: More than 300 times that of Earth's total mass.
- Hosts many moons, including the notable Galilean moons: Io, Europa, Ganymede, Callisto.
Saturn:
- Similar gaseous characteristics to Jupiter, renowned for its spectacular rings.
- Features numerous moons, including the prominent Titan.
Uranus:
- Smaller than the gas giants, yet larger than Earth.
- Unique for its extreme axial tilt and icy composition.
Neptune:
- Similar to Uranus with distinct hydrogen compounds constituting its atmosphere.
- Home to many moons, such as Triton.
Pluto & Charon:
- Notable for their small sizes and icy compositions.
- Charon is comparable in size to Pluto.

Beyond Neptune exists a variety of icy bodies classified as dwarf planets including Pluto, Eris, Makemake, and Haumea.
The International Astronomical Union (IAU) officially redefined the criteria for planetary status in 2006, categorizing these smaller planets as dwarf planets.