Solar System and Moon Notes

The Family of the Sun

• Regularities: All planets in our solar system orbit the Sun in the same direction and on roughly the same plane.

• Inner vs. Outer Planets:

  • Inner Planets (Mercury, Venus, Earth, Mars) are primarily made of rock and metal. They are smaller, more dense, and have fewer moons.

  • Outer Planets (Jupiter, Saturn, Uranus, Neptune) are gas giants composed mainly of hydrogen and helium. They are massive, have ring systems, and many moons.

• Comets, Meteors, and Asteroids:

  • Comets: These are icy bodies from the outer solar system. When they get close to the Sun, their ice vaporizes, creating a bright coma and a long tail that always points away from the Sun due to the solar wind.

  • Meteors: Known as "shooting stars," these are small pieces of rock or dust that burn up in Earth's atmosphere. Meteor showers occur when Earth passes through the trail of debris left by a comet.

  • Asteroids: These are rocky bodies, essentially "tiny planets." Most are found in the asteroid belt between Mars and Jupiter.

• The Inner Planets:

  • Mercury: It has extreme temperature differences between its sunlit and dark sides because it has almost no atmosphere to trap heat.

  • Venus: Our "sister planet" is similar in size to Earth but has a thick, toxic atmosphere that causes a runaway greenhouse effect, making it incredibly hot. Its slow, retrograde rotation means the Sun rises in the west.

  • Mars: The "Red Planet" is cold and has a varied landscape. There is strong evidence of past liquid water, and it's a topic of ongoing research whether life might have existed there.

• The Outer Planets:

  • Jupiter: This massive gas giant is almost a star. Its most famous feature is the Great Red Spot, a giant storm. Its moon Europa is a candidate for hosting life due to its subsurface ocean.

  • Saturn: Known for its prominent rings, which are made of billions of ice particles. Like Jupiter, it's a gas giant. Its moon Enceladus has geysers of water vapor, suggesting another potential for life.

  • Uranus, Neptune, and Pluto: Uranus has an unusual rotation, appearing to spin on its side. Pluto is now classified as a dwarf planet, distinguished from a planet by its inability to clear its orbital neighborhood of other debris.

• Connections and implications:

  • Understanding orbital regularities helps explain planetary motions and mission planning.

  • The split between inner rocky planets and outer gas giants suggests differences in formation and composition within the early solar system.

  • Ring systems and numerous moons around gas giants influence potential habitats and ongoing exploration.

  • The potential for life is especially discussed for moons like Europa (subsurface ocean) and Enceladus (water vapor geysers).

  • Real-world relevance: informs spacecraft design, mission targets, and interpretation of observational data from telescopes and space probes.

• Quick reference counts:

  • There are 4 inner planets: Mercury, Venus, Earth, Mars.

  • There are 4 outer planets: Jupiter, Saturn, Uranus, Neptune.

  • Pluto is classified as a dwarf planet.

The Moon

• Phases: The phases of the Moon are caused by the changing angles at which we view the Moon's sunlit surface as it orbits Earth.

• Eclipses:

  • Solar eclipse: occurs when the Moon passes between the Sun and Earth, blocking the Sun's light.

  • Lunar eclipse: occurs when Earth passes between the Sun and Moon, casting a shadow on the Moon.

• Surface: The Moon's surface is covered with mountains and flat, dark plains called maria. It has no atmosphere but may have water ice at its poles.

• Evolution: The Moon's surface has a violent past, marked by heavy cratering from asteroid impacts. It is much quieter now.

• Origin: The most widely accepted theory is that the Moon formed from the debris of a massive collision between a Mars-sized object and a young Earth.