Transcript Small Bodies of the Solar System

Small Bodies of the Solar System
Pluto, Comets, Asteroids,
Meteors and Zodiacal Light
PLUTO
God of the Underworld
Pluto Physical Data
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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
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Tilt of Axis: 96 (retrograde!)
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Surface Temperature: 43 K (-382 F)
Pluto Physical Data
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Orbital Semi-Major Axis: 39.44 AU
Orbital Period: 247.7 years
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Orbital Inclination: 17.2
Orbital Eccentricity: 0.250
Surface Gravity: 0.06 Earth gravity
Satellites: 3 known
Magnetic Field: unknown
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.
The Discovery of Pluto
January 23, 1930
January 29, 1930
The Plates on which Clyde Tombaugh found Pluto
Pluto’s 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.
• Pluto’s surface is probably
a methane and water ice
mixture (1) covering a
water ice mantle (2) with
an ice/rock core (3).
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
• Charon’s 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
Pluto’s Atmosphere
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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
Pluto’s Moon
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
Named after the
ferryman who rowed
souls across the River
Styx to Pluto's realm in
the underworld of Greek
and Roman mythology.
One of Christy’s images
Pluto’s Moon
• As seen by Hubble Space Telescope
Density 2.03 g/cm3
Charon
Density 1.65 g/cm3
70% rock and 30% water ice
much like Triton
Pluto
19,700 km
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.
Possible formation of Charon
Charon’s orbit within 0.001 deg of Pluto’s equator supports this scenario.
Pluto’s Orbit not so Strange anymore?
• Pluto’s Orbit is highly eccentric (0.250),
highly inclined to the plane of the solar
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system (17.2 ), and its orbit crosses
Neptune’s!
• From Jan 23, 1979 and until March 15,1999
Pluto was closer to the Sun than Neptune!
Pluto’s Orgin
• Since Pluto and Charon are thought to have
the same composition as Neptune’s 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
Many more Trans-Neptunian
objects now discovered
Neptune’s satellite Triton
Methane surface sprinkled by impact craters and geysers
Asteroids
The Asteroid Belt
Theory 1:
• Material between Jupiter and Mars tried to form a
planet when the Solar System was forming, but
Jupiter’s gravitational influence wouldn’t let it
happen
Theory 2:
• A planet did form between Jupiter and Mars
(Asteroidia), and some catastrophic event
destroyed the planet, leaving the asteroids
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
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
Particular Asteroids
IIDA and DACTYL:
• Ida was encountered by
the Galileo spacecraft in
1993
• Ida was found to have a
small satellite, Dactyl
• Dactyl’s 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.
Comets
Comet West
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.
Anatomy of a Comet
Direction
of Comet’s
Motion
Ion Tail
Coma
Nucleus
To Sun
Hydrogen Cloud
Dust Tail
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
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
Recent Comets
Comet Hale-Bopp in
March 1997
Image taken by J. DeBuizer and
J.Radomski of the University of
Florida Department of
Astronomy
Meteors, Meteorites, and Meteor
Showers
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 Earth’s surface
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
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.
Example of what we Learned
Temp. [K]
Heat from
Shock
waves in gas
… so gas
was there
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.
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
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 <3000/yr>. Watch out for statistics ….
(compare 2004 Asian tsunami above 226,000 fatalities)
Barringer crater in Arizona (1200 m in diameter, 200 m deep)
Fatality Probability
2004 Tsunami
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
Horizon
directly opposite the Sun,
called the gegenschein
Ecliptic
Zodiacal
Light
Sun
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