Exam 4 review

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Exam 4 review

• Chapter 15 Asteroids, meteors
• Chapter 17 The Sun

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Asteroids

• Sizes
• Up to 1,000 km diameter (Ceres), most catalogued
  are 100 km or less
• Discovery first was Ceres (Father Piazzi, 1801,
  looking for comets)
• About 120,000 cataloged
• Types C, S, M
• C-type carbon low albedo, 75 of all asteroids
• S-type higher albedo 15
• M-type moderate albedo, 10
• Asteroid belt
• Most asteroids (gt99) in main belt between
  Mars, Jupiter
• Kirkwood gaps caused by gravitational
  interaction with Jupiter
• All large asteroids are in main belt
• Exploration using spacecraft
• Several visits (e.g. Galileo, NEAR)
• pictures show potato shape, cratered surface
• NEAR landed on Eros, took pictures of surface
• Galileo discovered orbiting satellite
  (Ida/Dactyl)
• NEOs and Earth impacts
• NEO (Near Earth Objects) have orbits that could
  intercept Earth

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Meteors

• Terminology
• Meteor object entering atmosphere, shooting
  star
• Meteorite object that has landed on Earth
• Size
• Most are smaller than grain of sand
• Fireballs typically size of fist
• Origin
• Cometary debris
• Appear to originate from radiant fixed
  direction
• This is an illusion caused by Earths motion in
  its orbit
• Composition
• Stony most common, look like rocks with sooty
  exterior
• Iron very dense, about 10
• Sliced, etched have Witmannstaten pattern
  evidence of slow cooling
• Stony-iron rare
• Famous meteor showers
• Leonids (Novemer 16) from Comet Tempel-Tuttle
• Geminids (December 13) Asteroid 3200!

4
The Sun Fusion Energy source

• Fusion in core only, requires 15 MK temperature
• Age of Sun 4.5 billion yrs, lifetime 10 billion
  yrs
• Will use only 10 of hydrogen
• If all hydrogen fuel used, could shine for 90
  billion yrs!
• 4H -gt He4 gamma rays neutrinos
• Takes place in series of binary collisions only!
• 4 particles colliding simultaneously highly
  improbable
• Mass of He4 slightly less than 4xH gt mass
  converted to energy (E mc2)
• Energy produces gamma rays
• Gamma rays collide, scatter (random walk) in
  solar interior
• Heats gas in interior
• Gamma ray loses energy, eventually becomes
  visible photon
• Takes 100,00 yrs to escape
• Neutrinos also created
• Flow from core essentially unimpeded by solar
  mass
• Detect neutrinos on Earth using neutrino
  telescopes
• Located in deep mines to filter out cosmic rays
• solar neutrino problem

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Example of Mass Energy equation

• where E Energy produced by conversion of mass
  (Joules), m mass converted to energy (kg), c
  speed of light (3108 m/sec)
• Example A typical car traveling on the highway
  requires about 100,000 (105) Joules/sec to
  operate. How much mass would need to be converted
  to energy to operate the car continuously for ten
  years?
• Answer 10 years is 36002436510 3.2108
  seconds, so the total energy required is
• Solve for mass (m) required

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Solar interior, atmosphere

• Interior 3 zones
• Core 15 million ?K fusion
• Radiative zone energy transported by radiation
• Convective zone boiling gas
• Atmosphere 3 zones
• Photosphere surface 6,000 ?K
• Chromosphere 20,000 ?K
• Corona 1-2 million ?K seen only during eclipses

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Solar activity

• Sunspots
• Appear dark because of contrast with solar
  surface (temperature 4600?K vs. 5700?K)
• Large groups are 50,000-100,000 km
• Lifetimes typically few weeks
• 11-year sunspot cycle
• Sunspot number peaks every 11 yrs
• Sunspot latitude migrates in latitude (butterfly
  diagram)
• Maunder minimum (1680-1750)
• Corresponds to little ice age in Europe
• Sun-Earth connection
• Large storms (CMEs) hit Earth, cause aurorae in
  polar regions (magnetic field of Earth deflects
  particles
• CMEs speed V 400-1000 km/s, take several days
  to travel to Earth