Notes on Solar System Portrait, Properties, and Orbits (4.1)

4.1 Solar system portrait

• What’s in the solar system (overview):
  • The Sun accounts for about 99.8% of the system's mass.
  • 8 planets orbit the Sun.
  • Hundreds of planets’ moons: roughly 285 known moons around major planets (plus many more around dwarf planets).
  • Dwarf planets (and their moons): on the order of single‑ to multi‑digit numbers (e.g., 9 noted dwarfs in the diagram), alongside tens of thousands of asteroids.
  • Other components: comets, meteoroids, dust.
• Scale depiction notes:
  • The figure is not drawn to scale; it shows relative positions and major objects rather than exact sizes/distances.
  • Distances shown by a special symbol (often Ø) indicate distance from the Sun; diameter values are shown as the average or equatorial diameter when given.
  • Saturn’s ring system shown, but not to scale.
• Notable objects and features highlighted in the portrait:
  • Inner planets (Mercury, Venus, Earth, Mars) close to the Sun.
  • Gas giants (Jupiter, Saturn) with prominent moons such as Titan, Enceladus, Rhea, Dione, Tethys, Mimas, Hyperion, etc.
  • Uranus and Neptune with numerous moons (e.g., Titania, Oberon for Uranus; Triton for Neptune).
  • Kuiper Belt and Pluto/Pluto‑system shown as distant, with objects like Eris, Haumea, Makemake.
  • Ceres highlighted in the asteroid belt as a major dwarf planet.
• Distances and scales (from the diagram):
  • The scale is not literal; a separate scale line is provided showing distances from the Sun in astronomical units (AU).
  • 1 AU equals about $1 ext{ AU} = 149.6 imes 10^6 ext{ km}$.
• Context: this portrait combines the major bodies and belts that define the architecture of the Solar System (planets, dwarf planets, asteroids, comets, moons).

4.1 Solar system properties

• Table 4.1 (Properties of Some Solar System Objects) summarizes representative data for major bodies.
• Key categories included in the table:
  • Orbital Semimajor Axis (AU) – average distance from the Sun.
  • Orbital Period (Earth years) – time to complete one orbit around the Sun.
  • Mass (Earth masses) – mass expressed in units of Earth masses.
  • Radius (Earth radii) – radius expressed in Earth radii.
  • Known Moons – number of natural satellites.
  • Average Density (kg/m³) – bulk density; Earth is 1.0 in the density scale used in the table (Earth = 1 in the density column).
• Example data (common‑knowledge values aligned with the table’s intent, tabulated for quick reference):
  • Sun: mass ≈ $M<em>\bigodot \approx 1.989 \times 10^{30} \text{kg}$, radius ≈ $R</em>\bigodot \approx 6.96 \times 10^5 \text{km}$, density ≈ \rho_igodot \approx 1.41 \text{ g cm}^{-3}\, (1410 \text{ kg m}^{-3}).
  • Mercury: a ≈ $0.39\ \text{AU}$, P ≈ $0.24\ \text{yr}$, M ≈ $0.055\ M<em>\oplus$, R ≈ $0.38\ R</em>\oplus$, moons = 0, density ≈ $5.43\text{ g cm}^{-3}$.
  • Venus: a ≈ $0.72\ \text{AU}$, P ≈ $0.62\ \text{yr}$, M ≈ $0.82\ M<em>\oplus$, R ≈ $0.95\ R</em>\oplus$, moons = 0, density ≈ $5.24\text{ g cm}^{-3}$.
  • Earth: a = $1.00\ \text{AU}$, P = $1.00\ \text{yr}$, M = $1.00\ M<em>\oplus$, R = $1.00\ R</em>\oplus$, moons = 1 (the Moon), density ≈ $5.51\text{ g cm}^{-3}$.
  • Mars: a ≈ $1.52\ \text{AU}$, P ≈ $1.88\ \text{yr}$, M ≈ $0.11\ M<em>\oplus$, R ≈ $0.53\ R</em>\oplus$, moons = 2 (Phobos, Deimos), density ≈ $3.93\text{ g cm}^{-3}$.
  • Ceres (asteroid): a ≈ $2.77\ \text{AU}$, P ≈ $4.60\ \text{yr}$, M ≈ $0.00015\ M<em>\oplus$, R ≈ $0.073\ R</em>\oplus$, moons = 1, density ≈ $2.0-2.8\text{ g cm}^{-3}$.
  • Jupiter: a ≈ $5.20\ \text{AU}$, P ≈ $11.86\ \text{yr}$, M ≈ $318\ M<em>\oplus$, R ≈ $11.2\ R</em>\oplus$, moons ≈ 79, density ≈ $1.33\text{ g cm}^{-3}$.
  • Saturn: a ≈ $9.54\ \text{AU}$, P ≈ $29.46\ \text{yr}$, M ≈ $95\ M<em>\oplus$, R ≈ $9.45\ R</em>\oplus$, moons ≈ 62, density ≈ $0.69\text{ g cm}^{-3}$.
  • Uranus: a ≈ $19.19\ AU$, P ≈ $84.01\ yr$, M ≈ $14.5-15\ M<em>\oplus$, R ≈ $4.0\ R</em>\oplus$, moons ≈ 27, density ≈ $1.27\text{ g cm}^{-3}$.
  • Neptune: a ≈ $30.07\ AU$, P ≈ $164.8\ yr$, M ≈ $17\ M<em>\oplus$, R ≈ $3.9\ R</em>\oplus$, moons ≈ 14, density ≈ $1.64\text{ g cm}^{-3}$.
  • Pluto (Kuiper Belt object): a ≈ $39.5\ AU$, P ≈ $248.0\ yr$, M ≈ $0.002\ M<em>\oplus$, R ≈ $0.2\ R</em>\oplus$, moons ≈ 5, density ≈ $1.86\text{ g cm}^{-3}$.
• Notes on interpretation:
  • Densities are bulk averages and can vary with composition and porosity.
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