Solar System

solar system the sun and all of the planets and other bodies that travel around it

Planet any of the primary bodies that orbit the sun

Models of the Solar System

• Geocentric - Everything revolved around earth. (Aristotle and Ptolemy)

• Heliocentric – Planets revolved around the sun – Galileo - saw four moons

revolving around Jupiter (1610)

Some data to explain:

1. Planets isolated

2. Orbits ~circular / in ~same plane

3. Planets (and moons) travel along orbits in same direction…. same direction as Sun rotates (counter-clockwise viewed from above)

Lunar and Planetary Institute image at

http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=175

Some more data to explain:

4. Most planets rotate in this same direction

NASA images edited by LPI

Mercury 0° Venus 177° Earth 23° Mars 25°

Jupiter 3° Saturn 27° Uranus 98° Neptune 30°

And some more data to explain:

5. Solar System highly differentiated:

Terrestrial Planets (rocky,

dense with density ~4-5

g/cm3)

Jovian Planets (light, gassy,

H, He, density 0.7-2)

Images: Lunar and Planetary Laboratory:

http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=178

The Nebular Hypothesis

solar nebula a rotating cloud of gas and dust from which the sun and planets formed

Nebular Hypothesis

1. nebula begins to collapse because of gravity

2. Nebula rotates and flattens, warm near the center

3. Planetesimals form (a small body from

which a planet originated)

heavy elements (Fe, Mg, Si) form at high temps

Lighter elements (H, He, CH4) at lower temps

4. After ~10 million years, material in center of nebula hot

enough to fuse H

• “...here comes the sun…” NASA/JPL-Caltech Image at

http://www.nasa.gov/vision/universe/starsgalaxies/spitzer-20060724.html

5. Planetesimals grow, collide, and remove excess dust.

Formation of Solar System

When Did the Solar System Form?

• 4.56 billion years ago

• How do we know? (evidence for formation)

Meteorite photo by Carl Allen at

http://ares.jsc.nasa.gov/Education/Activities/ExpMetMys/..%5C..%5CSlideSets/ExpMetMys/Slides1-9.htm

•Lunar samples - 4.5 to 4.6 Ga

•Meteorites - 4.56 Ga

•Earth – 3.9 (or 4.4 Ga)

Lunar meteorite at

http://meteorites.wustl.edu/lunar/stones/mac88105.htm

We Can Also Look Around ….

Close-up of "Proplyds" in

Orion

Thanks Hubble!

Hubble images at

http://hubblesite.org/newscenter/archive/releases/nebula/emission/1994/24/image/a/ and

http://hubblesite.org/newscenter/archive/releases/nebula/emission/1994/24/image/b/