The Solar System

The Origins of the Solar System and Earth

An excellent place to explore the solar system is The Nine Planets

Warning! Kids, don't try this at home! Some of the pix below are big files, not very friendly to a dial-up connection.

Table of Planet Data

Some Solar System Basics

• "terrestrial" planets: make up the inner solar system
  • Mercury, Venus, Earth, (Moon), Mars
  • formed near Sun, where temperature high
  • composed primarily of rock (ultramafic silicate minerals) and metal (Fe/Ni)
  • relatively high densities, slow rotation, solid surfaces, no rings and few satellites
  • differentiation (similar to fractionation of magma)
    • radioactive elements heat interior, make it soft
    • Fe, Ni sinks to center: core
    • oxides, silicates rise: "mantle"
    • CO₂, H₂O escapes to surface
  • small planets (small gravity) couldn't keep H, He
  • date surfaces by crater counting, superposition, cross-cutting relationships; radiometric dates on lunar rocks helped calibrate crater flux
• "Jovian" planets: Jupiter, Saturn, Uranus, Neptune
  • large planets, large gravity, composed primarily of hydrogen and helium
  • low densities, rapid rotation, deep atmospheres, rings and lots of satellites.
  • Jove = Jupiter; far from Sun, cold, gaseous or icey, large

Planet Scaling Law

• big planet has less surface area relative to its volume (and mass) than small planet
• given same concentration of radioactive elements (primarily U, Th, K, but early in solar system history short-half-life Al, Mg isotopes were important), big planet will be hotter

Nebulae: Star Factories

Sun

• 99.85% of mass of Solar System
• H, He (traces of Fe, Si, O, Al, ...)
• nuclear fusion: H combines to form He; heavier elements manufactured
• rotation period: 27 days

Terrestrial (rocky) planets

Mercury

• closest to Sun: hard to see; Mariner 10 (1974)
• 2nd smallest planet
  • low gravity; no atmosphere
  • large surface to volume ratio
  • no tectonism; ancient surface (crater count dating)
• 75% Fe/Ni core by mass
• rotation period: 59 days (orbit period: 88 days; 2 to 3 tidal synchroneity) unfortunately for Arthur C. Clarke's colonists
  • 427^oC (800^oF) / -173^oC (-280^oF)
• Mercury Map

Venus

• similar in composition to Earth
• similar in distance from Sun to Earth
• slow retrograde rotation (period: -243 days); result of captured moon?
• similar in size to Earth
  • large enough to retain CO₂, H₂O: greenhouse effect
• CO₂ shrouds planet: radar altimeters; Pioneer Venus, Magellan
• Surface:
  • gently rolling plains; little relief; covered by lava flows
  • several broad depressions: Atalanta Planitia, Guinevere Planitia, Lavinia Planitia
  • two large highland areas: Ishtar Terra (~size of Australia), Aphrodite Terra (~size of South America)
  • still volcanically active, but only in a few spots; geologically rather quiet for past few hundred million years
  • pancake volcanoes (eruptions of very thick lava)
  • coronae (collapsed domes over large magma chambers)
• Images
  • Venus clouds
  • early radar image
  • topography
  • island arc?
  • plate tectonics?
  • Surface photographs from the Soviet Venera 13 spacecraft
  • "pancakes"
  • Pandora corona
  • large shield volcano Sif Mons
  • Eistla Regio
  • Aine Corona
  • Atla Regio
  • Sapas Mons
  • Magellan Radar

Earth

• tectonically active, surfaced extensively reworked
• approximately at triple point of H₂O
• why not CO₂ atmosphere?
• plate tectonics (map)
• Volcanism

Moon

• small or no Fe core
• moonquakes
• origin: fission, capture, binary accretion
• highlands
  • heavily cratered; 4.6 b.y.
  • anorthosite (Ca plagioclase feldspar)
• maria
  • less cratered; 3.9 - 3.2 b.y.
  • basalt floods impact craters
• Earth and Moon
• Life on Moon
• Near side
• Far side

Mars

• red planet: weathered basalt
• thin CO₂ atmosphere
• volcanically active
• once had H₂O? yes!
• Images
  • Deimos
  • Phobos
  • Viking 1
  • Viking 2
  • Viking 3
  • MARS_LANDFLOW.JPG
  • evidence of life?
  • olympus_mons_topview.jpg

Asteroids

• big meteorite
• 26 known asteroids larger than 200 km in diameter
• source of meteorites (Apollo asteroids)
• fit "Bode's law" which led to discovery of Uranus in 1781 and Ceres (1000 km asteroid) in 1802

Jovian (giant, gas) planets

• composed primarily of hydrogen and helium
• low densities, rapid rotation, deep atmospheres, rings and lots of satellites.
• Jove = Jupiter; far from Sun, cold, gaseous or icey, large

Jupiter

• more than twice mass of all other planets combined
• contains 30 Earth masses of silicate/iron
• 10 hr "day"; 16 moons
• strong magnetic field; liquid metallic H core
• Great Red Spot
• heat flow exceeds flux from Sun
• Galilean Moons
  • Io, Europa and Ganymede are locked together by tidal forces into a 1:2:4 orbital resonance and their orbits evolve together
  • mini solar system; decreasing density, like planets
• Images
  • Io: True and enhanced images
  • Io:sulfur eruption
  • Io changes from 1979 to 1996
  • Europa
  • Europa: cracks in ice
  • Europa: ice rafts
  • Ganymede
  • Ganymede cross-section: Life beneath the ice
  • Callisto
  • Callisto fault scarp

Saturn

• similar to Jupiter; rings; 17 moons
• density of 0.7 g/cc!
• Images
  • montage of Saturn and its moons
  • Saturn orbited by Rhea, Dione
  • Saturn's great white spot
  • Saturn ring-plane crossing
  • Saturn's rings, false color
  • Saturn's moons, labelled
  • Saturn's moons

Uranus

• blue because of absorption of red light by methane in upper atmosphere
• 1977: occultation; rings; spins on its side
• Voyager 2 discovered 10 small moons (5 large ones already known)
• names from writings of Shakespeare, Pope, not classical mythology
• have circular orbits in plane of Uranus's equator (at large angle to ecliptic).

Neptune

• Uranus's twin; rings;Triton

Pluto

• smallest planet; Pluto's orbit is so eccentric, it sometimes crosses the orbit of Neptune. From 1979  to 1999 Neptune was the most distant planet from the Sun; Pluto is now the most distant in 1999.
• Pluto and Charon pieces of Neptunian moon?
• composition unknown; density (~2 gm/cm3) indicates mixture of 70% rock, 30% water ice much like Triton