Discoveries of Planets

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• Discoveries of Planets
• Pluto
• Asteroids
• Comets
• Meteoroids
• Meteors
• Meteorites
• Meteor Showers

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William Herschel 1781 Found Fuzzy Thing in
Sky Moved Three Positions Orbit Elongated Comet Ci
rcular Planet Uranus
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50 Years Later Not Following Predicted
Orbit Perturbed Perturbation Undiscovered
Planet Observed by Galileo Credit for Discovery
Only After Repeated Sightings 1846 Leverrier Neptu
ne
Uranus
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Perturbations Percival Lowell Planet X Clyde
Tombaugh 1930
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announcement delayed Percival Lowells
birthday general position given skepticism orbit
calculation Stanford very eccentric orbit
comet? Flagstaff Object prediscovery
photo 1915 better orbit
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• Mass
• From Perturbations
• Comparable to Earth
• Size
• From Brightness and Distance
• Comparable to Earth

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• Brother of Jupiter
• Both his brothers have planets.
• Ruler of Hades
• A Cold Dark Place
• Pluto is cold and dark because its far from the
  sun.
• Visibility
• Pluto, the god, has a helmet of invisibility.
• The high eccentricity means it will sometimes be
  close and bright, but also far and dim.

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Occultation 1955
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• Mass
• From Perturbations
• Comparable to Earth
• Size
• No Occultation
• Much Smaller

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• Mass
• From Perturbations
• Comparable to Earth
• Size
• No Occultation
• Much Smaller
• Much Denser 33g/cm3

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• Mass
• From Orbit of Charon
• 1/500 Earth Mass
• Size
• No Occultation
• Much Smaller
• Much Denser 33g/cm3

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What perturbed Uranus and Neptune?
undiscovered planet? perturbations based on
masses of Uranus and Neptune Neptunes mass was
poorly known. perturbation calculations repeated
with correct mass perturbations disappear no more
planets in solar system
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1978 Discovery Charon Eclipses Predicted 1980 Star
ted 1985
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• Mass
• From Orbit of Charon
• 1/500 Earth Mass
• Size
• Eclipse Observations
• 2400 km

Planet?
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Qualifications for Planet
comets asteroids 1000 km Ceres Mercury Venus
orbit sun size mass moons atmosphere shape
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Terrestrial Earth Venus Mars Mercury Moon
Jovian Jupiter Saturn Neptune Uranus
Plutonoid Pluto Charon 1992 QB1 1993 FW 5145
Pholus
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m
time
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Pluto Triton

• Mass 1/500
• Diameter 2400 km
• Density 2 g/cm3
• Composition
• Temperature
• Distance From Sun

• 1/200
• 2700 km

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Debris

• Asteroids
• Comets
• Meteoroids
• Meteors
• Meteorites

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Debris

• Asteroids
• Comets
• Meteoroids

• Meteors

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Debris

• Asteroids

• Meteors
• Meteorites

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Debris

• Asteroids
• rock, glass, metal
• Comets
• ice, soot, sand, rock
• Meteoroids
• sand grains, ice, rock
• smaller, different origin

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parent body iron/nickel meteorites core of
planet? rock glass meteorites mantle of planet?
Main Belt Mars Jupiter
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Trojans Lagrange points named after Trojan and
Greek heroes in Trojan war Apollo family cross
Earth Orbit
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more Apollos Icarus Adonis Hermes
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more Apollos Icarus Adonis Hermes Daedalus Hephais
tos Cerberus
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Killer Asteroids
Apollo perturbations 1997 XF11 2028 prediscovery
asteroid tugboat
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Amor family nearly Earth-crossing perturbations
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Comets
Kepler Halley 1758
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soot
sand
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1986 2061 1910
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Origin of Comets
Oort Cloud perturbed Kuiper Belt periodic
comet evaporation meteor shower