ES 023Planet Earth: Shaken and

Stirred

ES 123 The Dynamic Earth

•Quick review of last class

•Hertzsprung-Russell diagram (star classification)

•A tour of the solar system

•How did the solar system form?

•Are we alone?

Mendeleev’s Periodic Law• Periodic variations in the properties of elements led Dimitri Mendeleev to organize the elements into the Periodic Table

Mass number

(A)

Number of protons (Z)

Number of

neutrons Hydrogen (1H) 1 1 0 Deuterium (2H) 2 1 1

Tritium (3H) 3 1 2

Uranium-235 (235U)

235 92 143

Uranium-238 (238U)

238 92 146

Atomic Isotopes

Hydrogen(92%)

Helium(7.8%)

Carbon (.03%) and Oxygen (.06%)

All other elements (.11%)

Composition of the universe

Interior of the Sun

• The sun has multiple layers (like an onion)

• The sun’s energy source is generated by H fusion at the core

• Heat escapes the core by radiation

• In the outer part of the sun, heat is transferred by convection

Evolution of a 15 solar-mass star

Element fused

Fusion product

Time Temp. (K)

Hydrogen Helium 1010 years 4x106 Helium Carbon > 106 years 1x108 Carbon O, Ne, Mg 1000 years 6x108 Neon O, Mg A few

years 1x109

Oxygen Si, S 1 year 2x109 Silicon I ron A f ew days 3x109

Source: In Quest of the Universe, Kuhn, 1998

Star Classification:Hipparchus of Rhodes

•Created a catalog of 850 stars, classified by brightness

• His brightness scale counts backwards, from 1st magnitude (brightest) to 6th magnitude (dimmest)

190 BC to 120 BC

• In 1856, Oxford astronomer Norman R. Pogson invented an apparent magnitude scale based on Hipparchus’ visual magnitudes

• According to this scale, an increase of 5 units corresponds to an object that is 100 times brighter

• An increase of 10 units corresponds to 10,000 times brighter (100x100)

Apparent Stellar Magnitude (m)

• Definition: Absolute stellar magnitude (M) is the apparent magnitude that a star would have if it were 32.6 light years from the Earth.

• Absolute magnitudes for stars generally range from -10 to +17.

• The Sun has an absolute magnitude of 4.83, quite average

Absolute Magnitude

Hertzsprung-Russell diagram

•Classification chart for stars

•Shows absolute magnitude versus temperature (colour)

•Developed in the early 20th century by Danish astronomer Ejnar Hertzsprung and American Astronomer Henry Russell

Hertzsprung-Russell diagram

Main SequenceSun

Giants

Super Giants

White Dwarfs

Stellar Evolution

•Stars on the main sequence are fueled by H fusion

•Near the end of its life, a star gets hotter and bigger (i.e., main -> giant), as it switches to He fusion, etc.

•Ultimately, a star may explode (nova) then become a white dwarf, a neutron star or a black hole

A tour of the solar system

The inner solar system

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

A tour of the solar system

The outer solar system

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

A tour of the solar system

Terrestrial planetsMercury

Venus

Earth

Mars

Jovian planets

Jupiter

Saturn

Uranus

Neptune

Pluto

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

Terrestial planets vs. Jovian planets

Terrestrial

Diameter < 13000 km

Two or fewer satellites

No rings

Density > 3.9 g/cm3

Solid surface

Jovian

Diameter > 48000 km

8 or more known satellites

All have ring systems

Density < 1.8 g/cm3

Primarily liquid

•Smallest planet

•Heavily cratered surface, like the moon’s.

• Studied by Mariner 10 spacecraft (1974 and 1975).

• Each day lasts 1.5 years

• Surface temperature variations are most extreme in the solar system (90 K to 700 K*)

Mercury

*To get degrees Celsius from degrees Kelvin, subtract 273.15.

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

• Most similar to Earth in size (95% of diameter, 80% of mass)

•Surface temperature 740

K, pressure = 90 bars

• Studied by Mariner 2 in 1962, and more than 20 spacecraft since

• Each day lasts longer than one year, retrograde rotation

Venus

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

• Surface area is about the same as the land surface area of Earth

•Most spectacular topography in the solar system

• Olympus Mons: 24 km high

• Valles Marineris: canyons 2 to 7 km deep

•Mariner 4 (1965), Viking (1976), Mars Pathfinder (1997), Mars Expedition (2004), 3 orbiters currently.

Mars

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

• More massive than the rest of the planets combined

• In 1994, Comet Shoemaker-Levy 9 collided with Jupiter

•Great red spot has persisted for > 300 years

•16 known moons

•Since Pioneer 10 (1973) visited by 5 missions including Galileo probe (1995-2003).

Jupiter

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

• 2nd largest planet in the solar system

•Rings are > 250,000 km in diameter, but only 1 km thick

•Less dense than water

•18 known moons

•Pioneer 11 (1979), then Voyager 1 and Voyager 2. Cassini (2004-2008)

Saturn

http://seds.lpl.arizona.edu/nineplanets/nineplanets/

Formation of the solar system

Orion nebula - “stellar nursery”

Two theories:

1. Solar system evolved from a nebula (dust cloud)

2. Solar system formed by catastrophic event

Catastrophic theories for the formation of the solar systemGeorges de Buffon (1745) – A comet collided with the Sun, expelling matter which accreted to form planets. Forest Moulton & Thomas Chamberlin (1900) – A star passed close to Sun, pulling away huge filaments of material.

Problems: such events are extremely rare. Also material is so hot that it would dissipate into space and not accrete.

Formation of the solar system

Nebular theory is more consistent with observations

e.g., All planets rotate in same direction and almost in the same plane (plane of the ecliptic)

Name Why

Earth :-)Mars most Earth-like; more so in the pastEuropa may have liquid waterTitan atmosphere like early Earth, liquids likelyIo complex chemistry, warmer than mostJupiter long shot: warm, plenty of organic material

The Best Prospects for Life

http://seds.lpl.arizona.edu/nineplanets/nineplanets/gif/NinePlanets.jpg