Solar System Debris

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Solar System Debris
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Solar System DebrisSolar System Debris

• Apart from the Sun (a large object) and the
  planets and larger moons (medium-sized objects),
  most of the other objects in the solar system can
  be classified as Solar System debris a
  collection of ice and rock fragments.
• Solar system debris comes in a number of forms,
  including asteroids, meteoroids, comets, dust,
  and Kuiper Belt Objects or Trans-Neptunian
  Objects).

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Solar System DebrisAsteroids

• History Bodes Law and the missing planet
• There are currently over 150,000 identified
  asteroids also known as minor planets.
  
• Ceres, at 1,000 km (600 mi) in diameter, is the
  largest asteroid and makes up 30 of the mass of
  all asteroids. It large enough to be round and is
  therefore considered to be a dwarf planet (see
  later).
• Pallas and Vesta have diameters greater than 500
  km.
  
• About 23 more asteroids have diameters between
  200 and 500 km.
  
• About 100 are larger than 100 km an all the rest
  are under 100 km in diameter.
  
• There are probably more than a million asteroids
  with a diameter greater than 1 km.
  
• If you put all the asteroids together they would
  produce an object barely over half the size of
  the Moon.

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Solar System DebrisAsteroids

• The Orbits of Asteroids
• The asteroids revolve around the Sun in a
  counterclockwise direction like the planets.
  
• Most asteroids orbit in or near the plane of the
  ecliptic.
  
• Most asteroids orbit the Sun at distances from
  2.2 to 3.3 AU (between Mars and Jupiter) in what
  is called the asteroid belt.

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Solar System DebrisAsteroids

• Apollo asteroids are some 50 asteroids with
  diameters larger than 1 km that have eccentric
  orbits that cross the Earths orbit (e.g. Eros).
  
• Asteroids are not evenly distributed across the
  asteroid belt.
  
• At certain distances - 2.5 and 3.28 AU - gaps
  appear and are related, respectively, to 1/3 and
  1/2 of Jupiters orbital period (resonances).
  
• These Kirkwood gaps are due to synchronous tugs
  (orbital resonances) from Jupiter.

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Solar System DebrisAsteroids

• The Origin of the Asteroids
• Astronomers originally thought the asteroids were
  due to an exploded planet, but there is no known
  mechanism for making a planet explode.
  
• Most likely the asteroids are primordial material
  that never formed into a planet because of
  Jupiters gravitational influence.

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Solar System DebrisMeteors

• Meteoroid is an interplanetary chunk of matter
  smaller than an asteroid.
  
• Meteor is the phenomenon of a streak in the sky
  caused by the burning of a rock or dust particle
  as it falls into our atmosphere.
  
• Meteorite is an interplanetary chunk of matter
  after it has hit a planet or moon.

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Solar System DebrisMeteors

• Meteors
• A meteoroids typical speed is 50 km/s, so when
  it hits the Earths atmosphere, it heats up and
  begins to vaporize.
  
• What actually lands on the Earth?
• Micrometer sized objects float down to the Earth
• millimeter-sized particles burn up in mesosphere
  (shooting star)
  
• Centimeter-sized particles burn up as a fireball
  (rare)
  
• Meter-sized particle strike ground (very rare)
• It is estimated that 1,000 tons of meteoritic
  material hit the Earth every day.

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Solar System DebrisMeteors

• Meteoroids
• It is estimated that only 1 in 1 million
  meteoroids that hit the atmosphere survives to
  reach the surface.
  
• Unlike most asteroids, meteoroids may orbit the
  Sun in any orientation.
  
• It is thought that many small meteoroids are
  debris from asteroid collisions.
  
• Many other meteors come from material evaporated
  from a comets nucleus.

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Solar System DebrisMeteors

• Meteor Showers
• Meteor shower is the phenomenon of a large group
  of meteors seeming to come from a particular area
  of the celestial sphere. The Earth actually
  passes through a swarm of small meteoroids.
• Radiant of a meteor shower is the point in the
  sky from which the meteors of a shower appear to
  radiate.
  
• Most of the major meteor showers are associated
  with comets.
  
• Some showers change in intensity from year to
  year because the swarm of particles that cause
  the shower clump together in one region of the
  comets orbit.

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Solar System DebrisMeteors

• Types of Meteorites
• In every case that someone has been able to track
  or film a meteor as it fell to the ground, the
  meteors have been discovered to originate from
  the asteroid belt
• There are two basic types of meteorites
• Primitive simple mixtures of rock and metal,
  sometimes also containing carbon compounds and
  small amounts of water
  
• Processed these appear to have undergone
  differentiation and have a core/mantle/crust
  structure. Some are made mostly of iron,
  suggesting they came from a core of a shattered
  asteroid. These are generally younger than the
  primitive meteorites.
• Both types are informative about the early
  history of the solar system.
  
• Some meteorites have come from the Moon and Mars.

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Solar System DebrisComets

• Edmund Halley, a friend of Newton, used Newtons
  methods, his own observations, and prior comet
  descriptions to calculate orbits for a number of
  comets.
• He correctly surmised that these prior comets
  were in fact the same comet. He correctly
  predicted the next return of the comet that was
  then named in his honor.
• Comet Halley is probably the most famous periodic
  comet.

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Solar System DebrisComets

• The planes of revolution of comets are not
  limited to the ecliptic but are randomly
  oriented.
  
• Consequently, comets sweep past the Sun from all
  directions.
  
• Periods of revolution vary from a few years to
  millions of years.

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Solar System DebrisComet Composition

• Head
• nucleus relatively solid and stable, mostly ice
  and gas with a small amount of dust and other
  solid
  
• coma dense cloud of water, carbon dioxide and
  other neutral gases sublimed off of the nucleus
  
• hydrogen cloud huge (millions of km in diameter)
  but very sparse envelope of neutral hydrogen
  
• Tail
• ion tail as much as 1 AU long composed of plasma
  and laced with rays and streamers caused by
  interactions with the solar wind.
  
• dust tail up to 10 million km long composed of
  smoke-sized dust particles driven off the nucleus
  by escaping gases this is the most prominent part
  of a comet to the unaided eye and is caused by
  interaction from solar radiation pressure.

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Solar System DebrisComets

• Fred Whipple proposed in 1950 that the nucleus of
  a comet is essentially a dirty snowball, as
  opposed to a traveling gravel bank.
  
• The composition of the nucleus is water ice,
  frozen carbon dioxide, other ices, and small
  solid grains.
  
• The nucleus also has a significant fraction of
  organic material.

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Solar System DebrisComets

• Giotto, a European spacecraft, revealed that
  Halleys coma is billions of times less dense
  than the atmosphere of the Earth at sea level.
  
• The nucleus of Comet Hale-Bopp is about 15 km
  across and spins once every 12 hours (very
  similar to what Giotto found for Halleys
  comet).
• As Hale-Bopps nucleus spun, material was ejected
  from it in geysers and spiraled away from it.

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Solar System DebrisRecent Comets

• Becomes bright/prominent when close to the Sun
• Dozens of faint ones seen per year
• A bright one seen once in 10 years
• Hale-Bopp (1997), Hyakutake (1996), West (1976)
• Halley (1986)
• Semi-bright NEAT, LINEAR and Bradfield (2004)
• Semi-bright Machholz (2004-05)
• Semi-bright SWAN (2006)
• The Great Comet McNaught (January 2007)

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Solar System DebrisDeep Impact to Comet Tempel
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• Objective Determine the structure and
  composition of comet Tempel 1
  
• Significance of results
• Comets formed in outer regions of the solar
  system
  
• Early planetary material still frozen inside
• We can learn much about the formation of the
  solar system by analyzing the composition of
  pristine comets
  
• Tempel 1 is a pristine or well-preserved comet

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Solar System DebrisDeep Impact Mission Results

• Mission Results
• July 3, 2005
• 820 lb Hammer Impacts Comet 9P/Tempel 1
• Ejected fluffy powder like talcum powder
• Mostly dust (silicates), steam and carbon
  dioxide
  
• Other compounds include carbonates, aromatic
  hydrocarbons
  
• Some ice found on surface (surprise!)
• Preliminary results indicate nucleus composition
  more like a fluff ball than an ice cube
  
• Scientific analysis ongoing

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Solar System DebrisComets

• Comet Tails
• A comets tail always points away from the Sun
  (and thus does not always follow the comets
  head).
  
• After passing the Sun, a comets tail actually
  leads the head.
  
• The comets straight (ion) tail consists of
  charged molecules (ions) which are dynamically
  influenced by the Solar Wind.
  
• The curved diffuse (gas) tail is caused by dust
  in the coma being pushed away by solar radiation
  pressure.

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Solar System DebrisComet Origins

• Öort cloud aphelia of billions of comets lie
  about 10,000 100,000 AU from the Sun,
  
• Proposed by Jan Öort in 1950
• Icy chunks of material ejected by Jovian planets
  in early solar system formation
  
• Today, a few are Perturbed by nearby stars and
  brought in
  
• Kuiper belt comets which lie just outside
  Neptune
  
• Includes Trans-Neptunian objects/Plutinos
• Pluto may be king of these objects

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Solar System DebrisComet Origins

• What is the fate of a comet?
• It can impact a planet or Sun
• Like Shoemaker-Levy 9 into Jupiter
• It can get ejected out of the solar system
• It can get put into a shorter orbit
• Eventually burns-out from repeated close
  encounters with the solar wind near perihelion
  which cause evaporation of nucleus and/or
  volatile material

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Solar System DebrisThe Discovery of Pluto

• Clyde Tombaugh used a blink comparator to compare
  two photos of the sky taken a few days apart.
  
• In 1989 Pluto was as close to the Earth as it had
  been for 248 years. (From 1979 to 1999 Pluto was
  inside Neptunes orbit.)
  
• Plutos average distance from the Sun is 40 AU,
  but its eccentric orbit causes it to vary in
  distance from 30 AU to 50 AU.

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Solar System DebrisPluto and Charon

• Stellar occultations indicate that Pluto has a
  thin nitrogen, carbon monoxide and methane
  atmosphere. At aphelion, it is probably too cold
  for Pluto to maintain an atmosphere.
• Plutos atmosphere limits an accurate
  determination of its size, which probably ranges
  from 2,362 to 2,412 km.
  
• In 1978, J. Christy discovered that Pluto has a
  moon, now named Charon (KAIR en or SHAHR en).

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Solar System Debris Pluto and Charon

• New Horizons Mission to Pluto
• Launched January, 2006
• Jupiter Flyby 28 Feb 2007
• First Flyby Opportunity July 2015
• Other Targets Centaurs and KBOs
• The two newest moons of Pluto (Nix and Hydra)
  were named not only because of there mythological
  connection to the underworld, but because the
  their initials are the same as those of the
  spacecraft mission to Pluto.

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Solar System DebrisPluto and Charon

• Charons diameter (1,200 km) is about half that
  of Pluto
  
• Plutos mass is about 12 times that of Charon but
  only 1/5 that of the moon
  
• Charon density 1.2-1.3 g/cm3 Pluto 1.8-2.1
  g/cm3
  
• Charon is less than 9 Pluto diameters away from
  Pluto (compare Moon ¼ diameter of Earth, and 30
  Earth diameters away from Earth)
  
• Charon orbit is tilted 119o to Plutos orbit
  around the Sun (i.e. it is in the equatorial
  plane of Pluto)
  
• Despite their small size, they are tidally looked
  in a 11 resonance with Charon orbiting Pluto
  every 6.4 days, the same as Plutos rotation
  
• But wait theres more!

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Solar System DebrisOrigins of Pluto

• A Former Moon of Neptune?
• Because Pluto is small and has an eccentric
  orbit, some theorize that it a former moon of
  Neptune that was somehow ejected.
  
• The discovery of Charon (and now 2 other moons)
  made it seem less likely that Pluto was once
  Neptunes moon.
  
• Also, the large difference in density between
  Charon and Pluto points to Charons capture by
  Pluto.

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Solar System Debris Origins of Pluto

• Planet, Asteroid, or ???
• Pluto doesnt fit the asteroid classification
  since its density and composition is more
  consistent with a satellite of Jovian planet
  
• In the 1990s Pluto was proposed to be the largest
  member of the plutino class objects found in
  the Kuiper belt.

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Solar System DebrisThe Kuiper Belt

• Kuiper Belt ???
• In addition to the Asteroid Belt, the Solar
  System appears to have a second belt, now called
  the Kuiper belt
  
• Support for this comes from the detection of
  about 600 small, presumably icy, bodies orbiting
  near and beyond Pluto (first object discovered
  was 1992QB1).
• Extent of belt is unknown, but statistical
  analysis indicates that the Kuiper belt may have
  an total mass far greater than that found in the
  asteroid belt.
• Objects in the belt are sometimes referred to as
  KBOs or plutinos, and Quaoar (found in 2002 with
  a diameter of 1250 km), Sedna (discovered in 2003
  with a diameter of 1600 km), and 2004DW are among
  its largest members.

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Solar System DebrisA New Planet?

• July 2005 Mike Brown and associates
  announced the discovery of 2003UB313 as
  the tenth planet
  
• 2003UB313 is just a bit larger than Pluto
• How can they know that?
• Discovered some 97 AU from the Sun, near its
  aphelion
  
• Its the furthest object detected in our solar
  system
  
• Huge 557-year eccentric orbit takes it within 38
  AU of Sun
  
• It was discovered to have a moon! But what to
  name these objects .

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Solar System DebrisThe Kuiper Belt

• Associations
• Tritons orbit is backwards and is highly
  tilted with respect to Neptunes equator Triton
  is perhaps a captured planetesimal from the
  Kuiper belt
• Short-period comets are now believed to be icy
  nuclei from the Kuiper belt
  
• The centaurs, of which Chiron is a well-known
  example, appear to originate from the Kuiper
  belt.
  
• 2003 UB313 (Eris) is a KBO larger than Pluto, in
  an orbit that crosses that of Pluto, and has a
  moon (Gabrielle?)
  
• Should Pluto still be considered a planet or a
  member of the Kuiper belt?

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Solar System DebrisGood-bye Planet Pluto

• Recently, Pluto was demoted from the ranks of
  planethood at the International Astronomical
  Union Meeting in August, 2006, to the status of a
  dwarf planet.
• A planet is officially defined as an object
• that is in orbit about the sun.
• has sufficient mass for its self gravity to
  overcome rigid-body forces so that it assumes a
  nearly round shape.
  
• has cleared the neighborhood around its orbit.
• A dwarf planet is officially defined as an
  object
  
• that meets the first two criteria of a planet,
  but not the third.
  
• Pluto, Eris, and Ceres are now dwarf planets
  others will most certainly follow.

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Solar System DebrisCollisions

• What happens when something strikes Earth?
• We have evidence of things hitting the Earth
• Craters, meteorites
• As a general rule the craters made by meteors are
  10 times bigger than the impactor
  
• The most prominent impact crater on Earth is
  Meteor Crater near Winslow, Arizona.
  
• There may have been impacts which affected life
  significantly
  
• Chicxulub meteor which landed off the Yucatán
  Peninsula may have wiped out the dinosaurs

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Solar System DebrisCollisions

• Have we ever witnessed a major impact?
• We have not witnessed a major impact on a solid
  body, but in 1994 Comet Shoemaker-Levy 9 (SL9)
  impacted into Jupiter.
  
• This event had 2 effects
• It was one of the best examples of international
  cooperation
  
• It made the public awareness of current nature of
  giant collisions in our solar system

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Solar System DebrisCollisions

• Did an impact kill the dinosaurs?
• We have identified more than 150 impact craters
  on the Earth
  
• One impact, off the coast of the Yucatan
  Peninsula, may have wiped out the dinosaurs 65
  million years ago
  
• Clues such as the deposit of iridium sediment
  (coming from an asteroid) at the right geological
  depth in the soil helps verify such a claim
  
• This meteor impact lead to a mass extinction
  where 99 (and 75 of the species) were
  extinguished

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Solar System DebrisCollisions

• Is the impact threat real?
• There are certainly many objects that could hit
  us we have detected over 800 asteroids over 1 km
  in size which pass near the Earths orbit.
  
• The threat is real, but the chances of something
  big hitting us in our lifetime is small
  
• Nevertheless, we were hit by a comet or asteroid
  in the region of Tunguska, Siberia in 1908
  resulting in a tremendous explosion. A hit like
  this over a major city would be devastating.
• If a big asteroid were headed for us, could we
  prevent the impact?

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The End