The Sun and the Origin of the Solar System

• Mid-sized, G-type main sequence star• Distance: 1 AU = 150 million km away• Size: Actual radius 700,000 km = 100 Earths• Temperature, Luminosity (surface) T = 6000 K

http://www.nasa.gov/multimedia/videogallery/index.html

• 99.86% of the total mass of the Solar System• 75% hydrogen, 23% heliun• 2% O, C, Ne, Fe

Sunspots• surface areas that are darker than

surroundings (lower temperatures)• regions of intense magnetic activity

Solar Evolution

Star (Sun) formation

Stellar Evolution

• The Sun is a middle-aged, low-mass, main-sequence star • 5 billion years ago:

– Beginning of its life on main-sequence – Sun had 1/3 luminosity it has now.

• 5 billion years from now: – End of its life on main-sequence – Sun will have twice the luminosity it has now.

• When H is exhausted, core shrinks. • Heats up• High temperatures ignites a shell of H around

the core. • Increased pressure drives the envelope of the

star outward. • Creates a Red giant

– Contraction of core, raises the temperature – Ignites He shell around the core – Eventually the core stabilizes– Envelope is ejected as a "planetary nebula" – The core remains as a "white dwarf"

Solar system formation

• Starting point: – A cloud of interstellar gas and dust, the

"solar nebula“– Most of it (98%) is hydrogen and helium, includes

dust grains of heavier material, formed in previous generations of stars.

• Contraction• Accretion disk• Protostar• Condensation• Planetesimals

http://www.youtube.com/watch?v=5l5mB-rFuGo

Asteroid Belt

• Small bodies in the inner solar system • Asteroid Belt between Mars & Jupiter. • Orbits are strongly influenced by

Jupiter. • Made of rock, metal, or a mix of the

two.

• >300,000 asteroidal objects • >150,000 with good enough orbits to give

official numbers • ~15,000 asteroids with official manes • When you know its orbit, you can name it.

Examples of asteroid names

• Ceres (largest – 914 km)• Eros (landed on in2001 Feb 12)

• Bach • Beethoven • Lennon

• McCartney • Santana • Clapton

Irregular shape• Too small for gravity to make them spherical

Composition of Asteroids

• C-type: "Carbonaceous" – mostly carbon-bearing materials. ~75% of all asteroids.

• S-type: "Silicaceous" - mostly of silicates (stony or stony iron). 17% of all asteroids.

• M-type: "Metallic" - probably iron-rich

Asteroid Origins

• fragments of larger, differentiated bodies shattered by collisions

• remnants of more primordial material that never got differentiated

Impact with Earth

Would disrupt climates and trigger mass extinctions

Meteoroids

• Chunks of rock & iron smaller than asteroids orbiting the Sun• Sizes range from grains to 100 meters across

Meteor

• Streak of light when a meteoroid enters the Earth's atmosphere

• Most are tiny grains• Meteor showers are trails of

debris left behind by passing comets

Meteorite

• Any remnant that reaches the ground intact.

Russian Meteorite

• http://www.youtube.com/watch?v=90Omh7_I8vI

Meteor Impacts• About 100 tons of meteoroids hit the Earth

each day• Most are no bigger than grains of sand or

smaller

Earth Impact Effects Program

http://impact.ese.ic.ac.uk/ImpactEffects/

Comets Small bodies consisting of aggregates of ices

mixed with rock & dust

• As they approach the Sun, they heat up and the ices sublimate (go from solid to gas):

Halley's Comet• In 1705, Edmund Halley computed the orbit of

the great comet of 1682 using Newton's laws • Found that orbit of 1682 comet was the same

as comets seen in 1531 & 1607. • Predicted return in 1758.• Seen again on Christmas day 1758, 12 years after Halley's death

Origin of Comets

• Short-period comets are from the Kuiper Belt• Long-period comets are from the Oort Cloud

Structure of Comets

• Nucleus: – Dirty snowball of ices & dust – >99% the mass of the comet

• Coma– Bright "head" of the comet– Low-density cloud of gas & dust sublimed off the

nucleus – Extends out to 100,000 km or more

• Comets have two tails– Dust Tail, dusty particles swept back in a curved

path by solar radiation, white– Ion Tail, ionized atoms & molecules swept straight

back by the solar wind, blue

Comet Orbits

• Typically have a high degree of eccentricity

http://www.windows2universe.org/comets/comet_model_interactive.html

Kuiper Belt• Region of the Solar System beyond the planets

extending from the orbit of Neptune (at 30 AU) to approximately 55 AU from the Sun

Oort Cloud

• Cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun.

• Nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun