Astro 1010: Exam 3 Study Guide

Astro 1010: Exam 3 Study Guide

Chapter 7: Our Planetary System

• Major Objects in the Solar System

  • One star
  • 8 planets
  • 5 dwarf planets (minimum)
  • 200+ moons
  • Millions of asteroids (estimated)
  • Trillions of comets (estimated)

• Patterns in the Solar System

  • Inner Solar System: Mercury, Venus, Earth, Mars, and the asteroid belt
    • Smaller, rocky, or metallic objects
    • Inner planets orbit the sun relatively close to each other.
  • Outer Solar System: Jupiter, Saturn, Uranus, Neptune, the Kuiper belt, and the Oort cloud
    • Larger, icy, or gaseous objects
    • Outer planets orbit the sun increasingly far apart.
  • All the planets orbit the sun in the same direction in which the sun spins.
  • Most of the planets rotate in the same direction in which the sun spins, although Venus rotates backward, and Uranus rotates “on its side”.
  • Most moons orbit their planets in the same direction their planet spins.
    • Retrograde motion: objects that orbit “the wrong way”.
    • Triton (the largest moon of Neptune) is an example of a retrograde moon.

Chapter 8: Formation of the Solar System

• Catastrophic Encounter Hypothesis

  • Material was ripped loose from the sun by a close encounter with another star. This eventually formed the planets in orbit around it.
  • Falsified: predicts very few planets in random, chaotic orbits around other stars, neither of which is true.

• Collapsing Nebular Theory of Planet Formation

  • The solar system began as a nebula (gas cloud) that imploded.
  • Conservation of angular momentum will flatten the nebula into an accretion disk. Most of the nebula’s mass fell into the center to form the sun. Leftover mass formed the planets, asteroid belt, etc.
  • Process has been observed directly in other nebulae and young stars.
  • Frost line: hydrogen-based compounds like water (H_2O) could only freeze into solids at a minimum distance from the sun.
    • Objects inside the frost line could only be made from rocky / metallic materials.
    • Objects beyond the frost line have rocky / metallic cores but are covered in hydrogen-based ices. Particularly massive objects (the early gas giants) even attracted hydrogen & helium gas from the accretion disk, growing enormous hydrogen & helium atmospheres.

• Stars like the sun shine through nuclear fusion, converting mass into energy. When stars “die”, the heavier elements produced by fusion are ejected and spread throughout the galaxy, enriching nebulae with these elements.

• The asteroid belt and the Kuiper belt were formed due to orbital resonances with Jupiter and Neptune respectively.

• Most impact craters were formed during the period of heavy bombardment early in the solar system’s history when leftover debris from its formation were still common.

• Planetesimal: the early “seeds” that grew through collisions with other objects into the planets.

• Earth’s moon formed through the collision between Earth and a Mars-sized planetesimal.

• Radiometric dating of asteroids confirm the solar system is about 4.5 billion years old.

Chapter 9: Planetary Geology

• Inner planets in order of increasing distance from the sun: Mercury, Venus, Earth, and Mars.

• Inner planets and Earth’s moon in order of increasing size: Earth’s moon, Mercury, Mars, Venus, and Earth.

• Planetary Interiors

  • Metallic core (densest materials)
  • Rocky mantle (mostly middle-density silicate rock)
  • Rocky crust (mostly lower density rocks)
  • Lithosphere: upper-most layers of a planet, composed of solid rock. Earth’s lithosphere includes all of the crust and the upper mantle.
  • Venus and Earth have mostly molten, convective mantles and liquid outer cores. Mercury, Mars, and Earth’s moon have cooled off more rapidly due to their smaller sizes and have more-or-less completely solid interiors.

• Planetary interiors were heated up by accretion and differentiation as they formed, as well as on-going nuclear decay in their cores.

• Planets cool off via thermal radiation.

• Planets can generate global magnetic fields if they have convective, fluid interiors and rotate rapidly. In the inner solar system, only Earth meets these criteria.

Chapter 10: Planetary Atmospheres

• Earth: mostly nitrogen and oxygen atmosphere

• Venus and Mars: mostly carbon dioxide atmosphere

• Mercury and Earth’s moon: no significant atmosphere

• Greenhouse effect: gasses such as water vapor and carbon dioxide slow the loss of heat from a planet’s surface, raising the average temperature.

• Atmospheric pressure decreases with greater height above a planet’s surface.

• Planets can lose atmospheric gas if it freezes and condenses as solids/liquids on the surface, as well as through thermal escape, impact events, and solar wind.

• Conservation of angular momentum causes large-scale winds to slow down as air moves from the poles to the equator. Causes the Coriolis effect: air swirls into spirals, causing hurricanes and similar atmospheric events.

Mercury

• Closest planet to the sun

• Oversized metallic core: outer layers of the planet may have been stripped away by a giant impact.

• Caloris basin: very large impact crater. The impact event caused earthquakes and warped terrain all the way on the opposite side of the planet.

• Highest temperature range of all of the planets.

• Locked in a 2-3 spin-orbital resonance.

• Most elliptical orbit of the 8 major planets; precession of the perihelion was a major proof of Einstein’s theory of relativity.

• Surface is heavily cratered, similar to the moon but lacking large maria.

Venus

• Second planet from the sun.

• Hottest of the planets.

• Extremely thick atmosphere for a rocky planet; atmosphere is the remnants of Venus’s evaporated oceans.

• High amount of deuterium indicates the loss of an ocean’s worth of hydrogen.

• CO_2 atmosphere composed of oxygen (from what was originally water vapor) that bonded with carbon from surface rocks.

• Clouds composed of sulfuric acid.

• Many volcanoes, and the surface is mostly volcanic plains.

Earth’s Moon

• Maria: dark regions on the moon’s surface.

  • Large volcanic plains that fill in massive craters and low-elevation areas.
  • Darker than surrounding rock due to the higher concentrations of iron.

• Ice in permanently shadowed craters at the poles (particularly south pole).

• Apollo 11: first mission to land humans on the moon’s surface. Members Neil Armstrong, Buzz Aldrin, and Michael Collins (last one stayed in orbit).

Mars

• Fourth planet from the sun.

• Two small moons that are captured asteroids. One (Phobos) is slowly spiraling into the planet. It will eventually break into a ring system or impact Mars.

• Thin atmosphere occasionally blows up global dust storms.

• Ice caps much like Earth. Axial tilt and rotation rate are also similar to Earth’s.

• A lot of evidence that water once flowed on the surface.

  • Planet cooled down, lost global magnetic field, and solar wind stripped most of the atmosphere away.
  • Oceans lost as a consequence of the above.

• Many large geological features: Olympus Mons (volcano), Valles Marineris (canyon), and Hellas Basin (impact crater).

Jupiter

• Most massive of the planets, arguably approaches the mass of the smallest stars.

• Great Red Spot is a 150-year-old (at least!) storm system similar to a hurricane.

• Structure: cloud layer above H/He gas, above liquid H layer, above metallic H layer, surrounding a rocky and metallic core.

• Four largest moons = Galilean Satellites (named for Galileo)

  • Io: extremely volcanic
  • Europa: may have a large subsurface ocean
  • Ganymede: largest moon in the solar system, larger than Mercury
  • Callisto: only Galilean moon not participating in an orbital resonance

• 95 moons in total.

Saturn and Planetary Rings

• Very similar to Jupiter, but less massive.

  • Coloration more muted because cloud layers are deeper in the atmosphere.

• Clearly distorted from a spherical shape by its rotation.

• North pole hexagon

• Titan: 2nd largest moon in the solar system, only moon with a thick atmosphere, only object other than Earth with surface liquids (ethane and methane).

• Gaps in rings represent orbital resonances with moons in orbit around Saturn, or where a small moon is orbiting within the rings themselves.

• Uranus has the second most extensive ring system. Jupiter and Neptune also have them, but they’re must less obvious.

• Rings formed by…

  • Moons “shattering” after they pass the Roche limit
  • Enceladus and other, similar moons ejecting ices into orbit (cryovolcanism)

Uranus and Neptune

• Near twins: both are blue “ice giants” with clouds of methane much bigger than Earth but much smaller than Jupiter and Saturn.

• Uranus: first planet to be discovered in modern times as opposed to being known throughout human history.

• Neptune: discovered shortly after Uranus, when astronomers noted the orbit of Uranus indicated there must be an unknown massive object pulling on it.

• Great Dark Spots of Neptune similar to the Great Red Spot of Jupiter, but periodically fades away and then reform.

• Triton: largest moon of Neptune, only large moon with a retrograde orbit, likely a captured Kuiper belt object.

• Voyager 2 is the only space satellite to have ever gotten a close-up view of Uranus and Neptune.

Exploration

• Mercury: Mariner and MESSENGER

• Venus: Venera missions (Soviet Russia), Magellan (USA), Venus Express Orbiter (ESA), Akatsuki (Japan)

• Luna: the Apollo missions

• Mars: Sojourner, Spirit and Opportunity, and Curiosity (all landers), Mars Odyssey (satellite)

• Jupiter: Pioneer 10, Galileo, Juno, and Europa Clipper

• Saturn: Cassini-Huygens

• All the gas giants: Voyager 2