Touring Our Solar System / Earth Moon system

Our Solar System: An Overview

  • The Sun contains 99.5% of the solar system’s mass.
  • The solar system revolves around the sun and consists of:
    • Eight planets and their satellites
    • Smaller bodies
      • Dwarf planets
      • Asteroids
      • Comets
      • Meteoroids

Nebular Theory

  • Describes the formation of the solar system.
  • The sun and planets formed from a solar nebula.
    • A rotating cloud of gas and dust.
    • The solar nebula contracted and formed a hot protosun.
    • Planetesimals formed, then became protoplanets.

Nebular Hypothesis

  • The solar nebula (gas) contracted, cooled, and condensed into dust-sized particles.
  • These particles accreted (stuck together due to collisions) into protoplanets (asteroid-sized bodies).
  • Protoplanets then formed larger planets.

The Planets: Internal Structures and Atmospheres

  • Two types of planets, based on location, size, and density:
    • Terrestrial (Earth-like)
    • Jovian (Jupiter-like)

Terrestrial Planets

  • Include Mercury, Venus, Earth, and Mars.
  • Small, dense, and rocky.
  • Large cores of iron and nickel.
  • Low escape velocities.
  • Thin atmospheres of carbon dioxide or nitrogen.

Jovian Planets

  • Include Jupiter, Saturn, Uranus, and Neptune.
  • Large, low density, and gaseous.
  • Massive.
  • Thick atmospheres composed of hydrogen, helium, methane, and ammonia.
  • High escape velocities.

Bodies with Atmospheres vs. Airless Bodies

  • Airless worlds have relatively warm surface temperatures and/or weak gravities.
  • Bodies with significant atmospheres have low surface temperatures and/or strong gravities.

Evidence of Past Events: Impact Craters

  • Result from planetary collisions with massive bodies.
  • More common in the early history of the solar system.
  • Thick atmospheres may cause impacting objects to break up.
  • Craters exhibit a central peak and ejecta lands in or near the crater.

Formation of an Impact Crater

  • A. The energy of a rapidly moving body is transformed into heat and shock waves.
  • B. The rebound of over-compressed rock causes debris to be explosively ejected from the crater. Some of this material may melt and be deposited as glass beads.
  • C. Large craters may contain areas of rock that was melted by the impact and a rebounded central peak.
  • D. Ejected material forms a "blanket" around the crater.

Earth’s Moon: A Chip Off the Old Block

  • Diameter of 3475 kilometers (2160 miles) is unusually large compared to its parent planet.

  • Density:

    • 3.3 times that of water
    • Comparable to Earth’s crustal rocks
    • Perhaps the Moon has a small iron core

  • Gravitational attraction is one-sixth of Earth’s.

  • No atmosphere.

  • Tectonics are no longer active.

  • The surface is bombarded by micrometeorites from space, which gradually makes the landscape smooth.

  • Earth is too small to have formed with a moon so large.

  • A captured object would have a more elliptical orbit, similar to those around Jovian planets.

  • Formed as a result of a collision between a Mars-sized body and semi molten young Earth.

    • Ejected debris was thrown into orbit around Earth.
    • Coalesced to form the Moon.

Lunar Surface

  • Maria (singular, mare), Latin for “sea”
    • Dark regions.
    • Fairly smooth lowlands.
    • Originated from asteroid impacts and lava flooding the surface.
  • Highlands
    • Bright, densely cratered regions.
    • Make up most of the Moon.
    • Make up all of the “back” side of the Moon.
    • Older than maria.
  • Craters
    • Most are produced by an impact from a meteoroid, which produces
      • Ejecta
      • Occasional rays (associated with younger craters)

Moon's Evolution - Three Phases

  • Original Crust (Highlands)
    • About 4.5 billion years old.
    • As the Moon formed, its outer shell melted, cooled, solidified, and became the highlands.
  • Excavation of Large Impact Basins
    • Between 3.2 and 3.8 billion years old.
  • Formation of Rayed Craters
    • Material ejected from craters is still visible.

Moon's Current Surface

  • Small mass and low gravity = no atmosphere and flowing water.
  • Weathering and erosion are absent.
  • No active tectonics.
  • Micrometeorites continually bombarded.
  • Covered with gray, unconsolidated debris (lunar regolith).

Phases of the Moon

  • New Moon
  • Crescent (waxing)
  • First Quarter
  • Gibbous (waxing)
  • Full Moon
  • Gibbous (waning)
  • Third Quarter
  • Crescent (waning)

Eclipses of the Sun and Moon

  • Eclipses are shadow effects that were first understood by the early Greeks.
  • Two types of eclipses:
    • Solar eclipse
      • The Moon moves in a line directly between Earth and the Sun.
      • Can only occur during the new-Moon phase.
    • Lunar eclipse
      • The Moon moves within the shadow of Earth.
  • For any eclipse to take place, the Moon must be in the plane of the ecliptic at the time of new- or full-Moon phase.
  • Because the Moon’s orbit is inclined about 5 degrees to the plane of the ecliptic, during most of the times of new and full Moon, the Moon is above or below the plane, and no eclipse can occur.
  • The usual number of eclipses is four per year.

Terrestrial Planets

Mercury

  • Innermost planet
  • Smallest planet
  • No atmosphere
  • Cratered highlands
  • Vast, smooth terrains
  • Very dense
  • Revolves quickly
  • Rotates slowly

Venus

  • Second to the Moon in brilliance
  • Similar to Earth in:
    • Size
    • Density
    • Location in the solar system
  • Shrouded in thick clouds
    • Impenetrable by visible light
    • Atmosphere is 97% carbon dioxide
    • Surface atmospheric pressure is 90 times that of Earth’s
  • Surface
    • Mapped by radar
    • 80% of surface is subdued plains mantled by volcanic flows
    • Low density of impact craters
    • Tectonic deformation must have been active during the recent geologic past
    • Thousands of volcanic structures

Mars: The Red Planet

  • 1/2 Diameter of Earth
  • 1 “year” = 687 Earth days
  • Surface temperatures range from -140°C to 20°C
  • Thin atmosphere of carbon dioxide (95%)
  • Topography
    • Pitted with impact craters, some imply permafrost beneath.
    • Red color due to iron oxide (rust).
    • 2/3 of the surface is heavily cratered highlands, evolved early in planet’s history.
    • 1/3 is plains, located in the north, of lava.
      • Possibly the smoothest surface in the solar system.
    • Tharsis bulge: enormous elevated region, appears to have been uplifted and capped with volcanic rock.
  • Volcanoes
    • Numerous large volcanoes—largest is Olympus Mons
    • Active as recently as a few million years ago.
    • Mantle plumes produced large volumes of lava, but no plate tectonics allowed it to accumulate to make enormous volcanoes.
  • Wind
    • Dominant force
    • Abundant dunes
  • Water
    • Considerable evidence indicates that liquid water flowed in the first billion years of Mars' past.
    • Carved enormous valleys by catastrophic floods.
    • Rounded grains on the surface imply long transport distances.
    • Ice is found within 1 meter of the surface.
    • Ice caps composed mainly of water ice.
    • Recurring slope linnae = streaks appear seasonally on steep, warm Martian slopes, thought to form from briny (salt) water.

Jovian Planets

Jupiter

  • Largest planet
    • 2.5 times more massive than the combined mass of the planets, satellites, and asteroids.
    • If it had been ten times larger, it would have been a small star.
  • Orbits the Sun in 12 Earth years.
  • Rapid rotation
    • Slightly less than 10 hours.
    • Slightly bulged equatorial region.
  • Banded appearance
    • Multicolored.
    • Bands are aligned parallel to Jupiter’s equator.
    • Generated by wind systems.
  • Great Red Spot
    • In planet’s southern hemisphere
    • Counterclockwise rotating cyclonic storm
  • Structure
    • Surface thought to be a gigantic ocean of liquid hydrogen.
    • Halfway into the interior, pressure causes liquid hydrogen to turn into liquid metallic hydrogen.
    • Rocky and metallic material probably exists in a central core.
  • Rings
    • Debris the size of smoke.
    • Believed to be due to impacts on moons Amalthea and Thebe.
  • Moons
    • At least 67 moons
    • Four largest moons (Galilean satellites, discovered by Galileo in 1610)
      • Io: Innermost moon, most volcanically active in the solar system due to tidal pulls.
      • Europa: May have liquid water.
    • Eight largest moons appear to have formed as the solar system condensed.
    • Many small satellites, probably captured objects or remnants of collisions.

Saturn: The Elegant Planet

  • Similar to Jupiter in its:
    • Atmosphere
    • Composition
    • Internal structure
  • Moons
    • 62 known moons, varying significantly in size, shape, origin.
      • Titan: The largest Saturnian moon (larger than Mercury).
      • Enceladus: Erupts fluid ice (cryptovolcanic).
  • Rings
    • Most prominent feature, discovered by Galileo in 1610.
    • Complex.
    • Composed of small particles (moonlets) that orbit the planet.
    • Most rings fall into one of two categories based on particle density.
    • Thought to be debris ejected from moons.
    • Origin is still being debated.

Uranus

  • Uranus and Neptune are nearly twins.
  • Rotates “on its side.”
  • Rings.
  • Large moons have varied terrains.

Neptune

  • Dynamic atmosphere
    • One of the windiest places in the solar system.
    • Great dark spot.
    • White, cirrus-like clouds above the main cloud deck.
  • 14 satellites
  • Triton: Largest Neptune moon
    • Orbit is opposite the direction that all the planet’s travel.
    • Lowest temperature in the solar system (-391°F).
    • Atmosphere of mostly nitrogen with a little methane.
    • Volcanic-like activity — cryovolcanism.
    • Composed largely of water ice, covered with layers of solid nitrogen and methane.

Small Solar System Bodies

Asteroids: Leftover Planetesimals

  • Most lie between Mars and Jupiter in the asteroid belt.
  • Small bodies—largest (Ceres) is about 620 miles in diameter.
  • Some have very eccentric orbits.
  • Many of the recent impacts on the Moon and Earth were collisions with asteroids.
  • Irregular shapes.
  • Recent landings on asteroids, but origin is uncertain.

Comets: Dirty Snowballs

  • Leftover material from the formation of the solar system.
  • Structure and Composition
    • Nucleus: small central body.
    • Rocky and metallic materials.
    • Frozen gases vaporize when near the Sun.
      • Produces a glowing head called the coma.
      • Some may develop a tail that points away from the Sun due to radiation pressure and the solar wind.
  • Origin
    • Kuiper belt: large group of icy objects in the outer solar system.
      • Pluto lies in the Kuiper belt.
      • Orbit Sun disc-shaped structure around Sun.
      • Leftover planetesimals.
    • Oort cloud: icy planetesimals in a spherical shell around the outer solar system.
      • Random orbits.
      • Loosely bound to the solar system.

Meteoroids

  • Called meteors when they enter Earth’s atmosphere.
  • A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet’s path.
  • Meteoroids are referred to as meteorites when they are found on Earth.
  • Meteorites: impact Earth’s surface, some make craters.
  • Classified by their composition:
    • Irons: mostly iron, 5–20% nickel
    • Stony: silicate minerals with inclusions of other minerals
    • Carbonaceous chondrites: contain simple amino acids and other organic material, basic building blocks of life
    • Stony-irons: mixtures
  • May give an idea as to the composition of Earth’s core.
  • Give an idea as to the age of the solar system.

Dwarf Planets

  • Orbit the Sun.
  • Not the only objects to occupy their area of space.
  • Pluto is the prototype of this new category.
  • Located in the Kuiper belt—a band of icy objects found beyond the orbit of Neptune.

Pluto

  • Not visible with the unaided eye.
  • Discovered in 1930.
  • Now classified as a dwarf planet.
  • Moon (Charon) discovered in 1978.
  • Average temperature is -210°C
  • Recent exploration reveals Pluto is an active body with several distinct terrains.