Small Bodies of the Solar System

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Small Bodies of the Solar System

• Pluto, Comets, Asteroids,
• Meteors and Zodiacal Light

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PLUTOGod of the Underworld
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Pluto Physical Data

• Discovered by Clyde W. Tombaugh in 1930
• Diameter 2294 km (0.18 Dearth)
• Mass 1.2x1025 g (0.002 Mearth)
• Density 2.03 g/cm3
• Rotation Period 6.39 days
• Tilt of Axis 96o (retrograde!)
• Surface Temperature 43 K (-382o F)

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Pluto Physical Data

• Orbital Semi-Major Axis 39.44 AU
• Orbital Period 247.7 years
• Orbital Inclination 17.2o
• Orbital Eccentricity 0.250
• Surface Gravity 0.06 Earth gravity
• Satellites 3 known
• Magnetic Field unknown

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The Discovery of Planet X?

• Discovered Feb 8, 1930 by then 24-year old Clyde
  Tombaugh by coincidence.
• The existence of a planet X was predicted by
  Percival Lowell using the same techniques that
  Leverrier used to find Neptune but turned out
  to be based on measurement noise.

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The Discovery of Pluto
January 23, 1930
January 29, 1930
The Plates on which Clyde Tombaugh found Pluto
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Plutos Surface

• This image was taken by the Hubble Space
  Telescope and is the best surface map yet made
• Only contrasts are seen, no features
• Pluto has not yet been visited by spacecraft but
  New Horizons is on the way. Stay tuned for
  2015.
• Plutos surface is probably a methane and water
  ice mixture (1) covering a water ice mantle (2)
  with an ice/rock core (3).

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Surfaces of Charon, Nix and Hydra

• This image was taken by the Hubble Space
  Telescope and is the best surface map yet made
• Only contrasts are seen, no features
• Charons surface is mostly water ice due to lower
  surface gravity.
• Nix and Hydra probably also have water ice
  surfaces

Nix and Hydra discovered in 2005 by the Hubble
Space Telescope's Pluto Companion Search Team
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Plutos Atmosphere

• Very thin atmosphere (when closest to Sun)
• Envelopes its moon too
• Mostly made of Nitrogen and Methane
• Atmosphere condenses and snows to the surface of
  Pluto and its moon when they are farther from the
  Sun

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Plutos Moon
Named after the ferryman who rowed souls across
the River Styx to Pluto's realm in the underworld
of Greek and Roman mythology.

• CHARON
• Discovered by James Christy in 1978
• Saw a bump move from one side of Pluto to the
  other about every six days
• About half the size of Pluto, orbits retrograde

One of Christys images
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Plutos Moon

• As seen by Hubble Space Telescope

Charon
Density 2.03 g/cm3 70 rock and 30 water ice
much like Triton
Density 1.65 g/cm3
Pluto
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Nix and hydra discovered in 2005 by the Hubble
Space Telescope's Pluto Companion Search Team
NOT picture. Best picture currently possible from
the ground.
Pluto system to be visited by the New Horizons
mission in 2015.
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Possible formation of Charon
Charons orbit within 0.001 deg of Plutos
equator supports this scenario.
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Plutos Orbit not so Strange anymore?

• Plutos Orbit is highly eccentric (0.250), highly
  inclined to the plane of the solar system
  (17.2o), and its orbit crosses Neptunes!
• From Jan 23, 1979 and until March 15,1999 Pluto
  was closer to the Sun than Neptune!

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Plutos Orgin

• Since Pluto and Charon are thought to have the
  same composition as Neptunes Triton, it is
  suggested that they might be escaped satellites
  of Neptune (dynamicists say no)
• Or Triton, Pluto and Charon all formed near
  Neptune as many other Kuiperbelt objects did and
  only Triton was captured

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Many more Trans-Neptunian objects now discovered
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Neptunes satellite Triton
Methane surface sprinkled by impact craters and
geysers
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Asteroids
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The Asteroid Belt

• Theory 1
• Material between Jupiter and Mars tried to form a
  planet when the Solar System was forming, but
  Jupiters gravitational influence wouldnt let it
  happen
• Theory 2
• A planet did form between Jupiter and Mars
  (Asteroidia), and some catastrophic event
  destroyed the planet, leaving the asteroids

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The Discovery of Asteroids

• On the first day of the 19th C. (Jan 1,1801),
  Ceres (the largest known asteroid) was discovered
  by Giuseppe Piazzi
• By the end of the 19th C., several hundred were
  known
• We now know of more than 10,000

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Particular Asteroids

• CERES
• The largest asteroid by far
• Diameter 914 km
• Contains 25 of the mass of all the asteroids
  combined.
• The water asteroid having more water than the
  Earth
• Dawn to arrive at Ceres 2015, Vesta in 2011.
• The next largest are Pallas, Vesta, and Hygiea
  which are between 400 and 525 km in diameter
• All other known asteroids are less than 340 km
  across

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Particular Asteroids
IIDA and DACTYL

• Ida was encountered by the Galileo spacecraft in
  1993
• Ida was found to have a small satellite, Dactyl
• Dactyls size is 1.6 x 1.2 km, and orbits 90 km
  above Ida

Dactyl was blasted of Ida and will eventually
fall back. Many asteroids were smashed-up and
reassembled.
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Comets
Comet West
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Comet Basics

• Comets are mostly (50) water ice
• Comets are referred to as dirty snowballs
• They are a mixture of water ice, frozen gases,
  and silicate materials
• Comets have very eccentric orbits because their
  orbits have been recently perturbed sending them
  much closer to the Sun.
• They only have tails when close to the Sun
• The tails are made of gas and dust released by
  the comet.

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Anatomy of a Comet

Ion Tail
Direction of Comets Motion
Coma
Nucleus
Hydrogen Cloud
Dust Tail
To Sun
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History of Comets
m
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Comet Halley

• Orbits Sun every 76 years
• Furthest point in its orbit is just beyond the
  orbit of Neptune
• Nucleus 15 x 8 x 8 km
• Rotates every 7.6 days

1986 Halley mission first picture of a comet
nucleus
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Recent Comets

• Comet Hyakutake in March of 1996

Image taken by J. De Buizer and J. Radomski of
the University of Florida Department of Astronomy
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Recent Comets

• Comet Hale-Bopp in March 1997
• Image taken by J. DeBuizer and J.Radomski of
  the University of Florida Department of Astronomy

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Meteors, Meteorites, and Meteor Showers
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Meteor Nomenclature

• Meteoroids - interplanetary debris
• Meteor - Also called shooting star
• When a meteorite has entered the
• atmosphere creating a streak of
  light
• Meteorite - Those few meteoroids that make
• it to the Earths surface

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Types of Meteorites
IRONS

• Mostly made of iron with about 9 nickel

STONES

• Primarily silicates similar to Earth rocks

STONY-IRONS

• Mixture of the above two types

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Iron Meteorite Lodged in Tree Trunk
Meteorite interiors remain cold throughout
atmospheric flight and can therefore preserve
valuable information on how the solar system
formed.
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Example of what we Learned
Heat from Shock waves in gas so gas was there
Temp. K
Some inclusions formed in an oxygen-rich
environment and date to 4.567 billion years old,
while other chondrules were formed in an oxygen
setting much like that on Earth and date to 4.565
billion, or less, years old.
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Meteor Showers

• Associated with debris left behind by comets
• Typically very small meteoroids, so no meteorites
  are produced during a shower
• Can be as many as 100 meteors per hour in a good
  shower

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Meteor Impacts

• One catastrophic meteor impact every 26 million
  years on average
• Might have been responsible for dinosaur
  extinction
• Earth population of 7.6 billion means fatalities
  are lt3000/yrgt. Watch out for statistics .
• (compare 2004 Asian tsunami above 226,000
  fatalities)

Barringer crater in Arizona (1200 m in diameter,
200 m deep)
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Impact frequency
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Fatality Probability
2004 Tsunami
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Zodiacal Light and Gegenschein

• Zodiacal light is due to dust, concentrated in
  the plane of the solar system, that reflects the
  light of the Sun towards our eyes
• Reflection from the dust also causes a patch of
  light directly opposite the Sun, called the
  gegenschein

Ecliptic
Zodiacal Light
Horizon
Sun
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Zodiacal Light and Gegenschein

• The zodiacal light in the eastern sky before the
  beginning of morning twilight.
• The planet Venus and the open cluster M44 are
  also visible in this photograph.

Zodiacal Light