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 ndex.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

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 8vI 8vI

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

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 & Predicted return in 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 et_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 SunSolar SystemorbitNeptune AU Sun

Oort Cloud Cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun.comets AUlight-yearSun Nearly a quarter of the distance to Proxima Centauri, the nearest star to the SunProxima Centauristar