Vagabonds of the Solar System

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Vagabonds of the Solar System

• Asteroids
• Comets
• Meteoroids, Meteors, Meteorites

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Asteroids

• As solar system was forming, matter with too much
  angular momentum to fall into the sun coalesced
  at varying distances from the sun into
  planetesimals.

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Asteroids

• Many collided, forming planets and larger moons.
  
• Others were captured whole by planets as small,
  irregularly shaped moons
• Many still orbit the Sun. These are asteroids.

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Discovery of asteroids Part 1

• Ceres was the first asteroid discovered on New
  Years Day in 1801.
• It was discovered because it changed position
  every night
• Ceres is huge.
• Ceres accounts for 30 or the mass of all known
  asteroids
• Pallas was the next asteroid discovered 1803
• It was discovered because it changed position
  every night
• Only two more, Juno and Vesta, were found until
  mid 1800s

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Discovery of asteroids Part 2

• By mid 1800s, improved telescopes were available
• Most asteroids are very small compared to Ceres
• New telescopes made it possible to see smaller
  asteroids
• Most are lt1km across
• About 300 asteroids found lying between orbits of
  Mars and Jupiter
• This region is called the asteroid belt the
  asteroids are called belt asteroids

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Discovery of asteroids Part 3

• Applied photographic technique in 1891 introduced
  by Max Wolf
• Take long exposures and look for tracks made by
  asteroids
• Wolf discovered 228 asteroids this way

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Discovery of asteroids Part 4

• Improved digital image processing
• Dont waste telescope time on long exposures
• Take multiple images and subtract
• LINEAR
• NEAT

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LINEAR (Lincoln Near Earth Asteroid Research)

• The GTS-2 telescope is a 1 meter folded prime
  focus Cassegrain design identical to that of the
  Ground-based Electro-Optical Deep Space
  Surveillance (GEODSS) telescope used by the Air
  Force for space surveillance. It is located at
  the Experimental Test Site on White Sands Missile
  Base in NM
• Take several images of same view each night
  subtract to detect new objects

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NEAT (Near Earth Asteroid Tracking)

• NEAT detects moving objects - asteroids and
  comets - by observing the same part of the sky 3
  times during an interval of about 1 hour. The
  automatic data analysis system searches for
  moving objects by comparing the 3 images.
• The NEAT system is now mounted on the Maui Space
  Surveillance Site (MSSS) 1.2-m GEODSS telescope
  (same as LINEAR).

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Discovery of asteroids Part 5

• Estimate there are gt1,000,000,000 asteroids in
  the solar system

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Origin of asteroids

• Most likely the force of Jupiter on the
  planetesimals kept them from coalescing into one
  object
• Less likely that they had been one object and
  were split into many
• If all of the asteroids in the asteroid belt were
  put together to form a planet, it would be very
  small, smaller than Pluto.

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But some may be fragments of larger asteroids

• Some may break apart but not have enough speed to
  escape each others gravitational attraction, so
  reassemble
• Some large fragments end up orbiting near each
  other or even in contact

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4 asteroids have been imaged at close range

• The Galileo spacecraft (while on its way to
  Jupiter) imaged Gaspra and Ida.
• Gaspra and Ida have different amounts of
  cratering, so may have been broken apart from
  their parent asteroids at different times

Ida
Gaspra
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4 asteroids have been imaged at close range

• The NEAR (Near Earth Asteroid Rendezvous) mission
  did a flyby of Mathilde and orbited Eros.

Eros
Mathilde
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NEAR landed on Eros

• The touchdown speed of less than 4 miles per hour
  was one of the softest planetary landings ever.
• Team members then commanded craft's gamma-ray
  spectrometer to gather data on the elemental
  composition on and just below the asteroid's
  surface.

Eros landing site
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Some asteroids have satellites

• At least 2 asteroids have moons

Dactyl
Ida and Dactyl
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Asteroids outside the asteroid belt

• Some have highly elliptical orbits that bring
  them inside the orbits of some planets
• Apollo asteroids cross Earths orbit
• There are about 300 known Earth-crossing
  asteroids
• Amor asteroids cross Mars orbit
• Some asteroid orbits extend beyond Plutos orbit

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Asteroids outside the asteroid belt

• Some are located at stable Lagrange points
• There are 460 asteroids in Jupiters Lagrange
  points, called Trojan asteroids
• An asteroid has also been discovered at one of
  the Earths Lagrange points

L4 and L5 are stable L1, L2, and L3 are unstable
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Comets

• Comets formed near Uranus and Neptune, where
  water was plentiful and the temperature was low
  enough for ice to condense with roughly equal
  amounts of rocky and metallic material into
  bodies that still orbit the sun
• Gravitational forces from Uranus and Neptune
  flung the comets in every direction

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Kuiper belt

• Kuiper belt
• Centered on the ecliptic extending beyond the
  orbit of Pluto.
• Largest comet is 1/5 size of Pluto
• 200,000,000 comets

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Oort cloud

• Oort cloud
• NOT centered on the ecliptic but is a spherical
  distribution around the Sun extending about about
  50,000AU. 1/5 of the distance to the nearest star
• Can even have orbits perpendicular to the
  ecliptic
• Several billion comets
• A few pass through the inner solar system as
  Hale-Bopp and Hyakutake

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Comets

• Structure
• Because the Kuiper belt and the Oort clouds are
  far from the Sun, comets are completely frozen.
• As a comet approaches the sun, some of the ice
  vaporizes forming an atmosphere around the
  nucleus called the coma.
• The comet nucleus is only 10km across, but the
  coma can extend a million km across
• The hydrogen envelope surrounds the nucleus

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Comet tails

• Tail
• The tail develops from coma gases that are pushed
  outward by the solar wind
• This is why the solar wind was initially
  predicted
• The existence of the solar wind was verified by
  Mariner 2

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Comet tails

• Two types of tails
• Gas (or ion) tail
• Positively charged ions are pushed away from the
  Sun by the solar wind
• Always points away from the Sun
• Dust Tail
• Formed when photons strike dust particles that
  have been freed from the comets evaporating
  nucleus
• These particles are massive enough not to flow
  straight away from the sun, so lie between the
  gas tail and the direction of the comets motion

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Comet tails
Hale-Bopp
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Compositon of comets

• Stardust
• The goal of the Stardust mission is to return
  both particle samples from a comet and
  interstellar dust. By returning these samples to
  Earth for analysis a great deal is expected to be
  learned about the composition of the early
  universe.

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Comet orbits

• Long period comets
• Most move so fast that they leave the inner solar
  system after one pass by the Sun and take
  millions of years to return
• Short period comets
• Some pass near a planet which changes their
  orbit, slows it, and traps it in an orbit in the
  inner solar system.
• These comets may then have orbits of a few
  hundred years or less (as Halley)

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Comet lifetime

• Comets lose mass ( about 1/60 - 1/100 of its
  mass) every time they pass the Sun
• After its ices have all evaporated, the remaining
  dust and rock spread out in a loose collection
  the continues to circle the Sun along the comets
  original orbit
• When the earth passes through this collection, we
  see a meteor shower
• 30 meteor showers can be seen each year

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Comet lifetime

• A comet can be torn apart if it comes too close
  to a planet, like Comet Shoemaker-Levy 9 which
  fragmented in the tidal force from Jupiter

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Comet lifetime

• Comet LINEAR Breaks Up

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Meteoroids, Meteors, Meteorites

• Meteoroids
• Rocky and metallic debris smaller than asteroids
  (10s of meters across to microscopic) scattered
  throughout the solar system
• Some are broken off from asteroids of from
  planets, but some were never part of a larger
  body
• Meteors
• When a meteoroid is pulled by Earths gravity
  into Earths atmosphere, air friction creates so
  much heat that the outer layer vaporizes
• Common names are shooting stars, bolides, and
  fireballs
• Meteorites
• Meteors that reach the ground before completely
  vaporizing

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Impact craters

• Any meteor that survives passage through the
  atmosphere may leave an impact crater a comet
  back to Earth
• Barringer (or Meteor) Crater in Arizona which
  formed about 50,000 years ago
• Tunguska mystery
• Allende meteorite
• Alvarez discovery

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95 Worlds and Counting

• Film
• Tour of the satellites of planets in our solar
  system

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Vagabonds of the Solar System

• On the morning of his departure he put his planet
  in perfect order. He carefully cleaned out his
  active volcanoes. He possessed two active
  volcanoes and they were very convenient for
  heating his breakfast in the morning. He also had
  one volcano that was extinct. But, as he said,
  "One never knows!" So he cleaned out the extinct
  volcano, too. If they are well cleaned out,
  volcanoes burn slowly and steadily, without any
  eruptions. Volcanic eruptions are like fires in a
  chimney.

The Little Prince