Astronomy 121, Winter 2005

Exam 3 Review

Feb 23, 2005, jebPRELIMINARY



Basic Properties of Uranus, Neptune, and Pluto


Planet order
. from Sun
Orbital period
Semi-major axis
Mass

Radius
Density
Surface Gravity
Escape speed
Rotational Period

Axial Tilt
. (Inclination)
Surface Mag. Field
Surface Temp.
Known Moons

Uranus

7
84 years
19.2 AU
14.5 x Earth

4.0 x Earth
1270 kg/m3
0.9 x Earth
21 km/sec
-0.72 days

98o

0.74 x Earth
58 K
27

Neptune

8
164 years
30.1 AU
17.1 x Earth

3.9 x Earth
1640 kg/m3
1.2 x Earth
24 km/sec
0.67 days

30o

0.43 x Earth
59 K
13

Pluto

9
248 years
39.5 AU
0.002 x Earth

0.2 x Earth
2060 kg/m3
0.07 x Earth
1.2 km/sec
-6.4 days

118o

?
50 K
1




Discovery of the Outer Planets


Space Probes to the Outer Planets




Uranus and Neptune

Outer Worlds of the Solar System

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lecture on Uranus and Neptune

Rotation and Tilt of Uranus Largest moon of Neptune (Triton) has Nitrogen atmosphere and active geysers



Common Properties of Uranus and Neptune
the Outer Jovian Planets





Atmospheres of Uranus and Neptune


Comparison of the Elemental Makeup of the Jovian Atmospheres

Jupiter

Saturn

Uranus

Neptune

hydrogen

86%

92%

84%

84%

helium

14%

7%

14%

14%

methane

trace%

0.2%

2%

3%

ammonia

trace%

0.02%

0%

0%




Atmospheres of Uranus and Neptune


Color Weather

Rings of Uranus and Neptune


All of the Jovian Planets have rings


Rings of Uranus


Rings of Neptune

General Theory of Rings of the Jovian Planets

Magnetospheres and Internal Structure
of Uranus and Neptune



Internal Structures of Uranus and Neptune

Magnetospheres of Uranus and Neptune

Moons of Uranus and Neptune


Moons of Uranus

Moons of Neptune

Pluto
Outer World of the Solar System

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lecture on Pluto

Orbital Properties of Pluto Pluto's moon, Charon Pluto's other properties Pluto's origin




Solar System Debris
Keys to Our Origin
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lecture on Solar System Debris

Asteroids

Asteroid belt
  • Over a hundred-thousand rocky objects
  • largest: Ceres
    • 940 km diameter
  • All asteroids have mass of about 10% MMoon
    • small fraction of the Solar System
  • Prograde orbits, except 1
  • Jupiter's gravity continuously disturbs these chuncks of matter, preventing them from accumulating (favored theory for existence)
    • unlikely that these are fragments of a planet that broke up long ago
Types of Asteroids
  • C-type
    • carbonaceous(largely carbon, dark)
    • 75% of the asteroids
    • outer orbits
    • very old (4.6 billion years)
  • S-type
    • silicate(largely silcon, light)
    • 15% of the asteroids
    • inner orbits
  • M-type
    • nickel-iron
    • about 10% of the asteroids
Earth and Mars Crossing Asteroids
  • Apollo asteroids
    • Earth crossing with semi-major axis greater than 1 AU
  • Aten asteroids
    • Earth crossing with semi-major axis less than 1 AU
  • Amor asteroids
    • Mars crossing
  • all the Earth crossing asteroids will eventually collide with the Earth
    • this occurs about 3 times every million years
Orbital Resonances of Asteroids Close-up Views of Asteroids
  • Gaspra
    • S-type, maximum diameter of 20 km, about 200 million years old, fragment of larger object
    • visited by Galileo (on journey to Jupiter)
  • Ida
    • S-type, maximum diameter of 60 km, about 1 billion years old, fragment of larger object
    • tiny moon: Dactyl (1.5 km across)
    • visited by Galileo (on journey to Jupiter)
  • Mathilde
    • C-type, low density of 1400 kg/m3, porous interior
    • visited by NEAR-Shoemaker on way to Eros on June 27,1997
  • Eros
    • S-type, (33 km x 13 km x 13 km), 2700 kg/m3, appears homogeneous, not porous as Matilde
    • NEAR-Shoemaker (Near Earth Asteroid Rendezvous) - official web site
      • spacecraft misson to rendezvous with asteroid Eros
      • launched February 17, 1996
        • planned Eros rendezvous in early 1999
      • orbited Eros beginning February 14, 2000
        • orbited Eros for a year to do detailed study
        • crater densities indicated Eros is old, like Ida and Matilde, but unlike Gaspra
      • landed on Eros, February 12, 2001
  • Collisions with Earth
    • about 3 asteroids collide with the Earth per a million years
    • 65,000,000 years ago - ???

Comets

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  • Icy matter ("dirty snowballs") in highly elliptical orbit
  • unchanged since the formation of the Solar System
  • heat up, emit radiation, and develop tail as they near the Sun
Comet Structure
  • Nucleus - few km in diameter
    • Density : 100 kg/m3
    • Evaporation Rate: 10 tons/ second near the Sun
    • Lifetime: about 5000 orbits or about 400,000 years for Halley's Comet (in other words - short on cosmological scale)
  • Coma- evaporated gas and dust forms halo around nucleus as comet approaches the Sun
  • Hydrogen envelope
  • Two tails
    • ion tail (straight out, blown by solar wind)
    • dust tail (broad, diffuse, curved, less deflected by solar wind)
Two sets of orbits Halley's Comet
  • period of 76 years
  • retrograde orbit
  • Observation recorded every 76 years since 240 BC
  • In 1705, Edmund Halley realized the repeated appearances
    and predicted that this comet would reappear in 1758
    • comet appeared right on schedule in 1758 (after Halley's death in 1742)
Comet Shoemaker-Levy Impact on Jupiter in 1994
  • July, 1992 passed within Roche Limit of Jupiter -> broke apart
  • Discovered in March, 1993
  • Comet Shoemaker-Levy crashed into the surface of Jupiter in July, 1994
  • Series of impacts
Comets of 1996/1997
  • Hyakutake
    • in January of 1996, an amateur comet astronomer in Japan discovered this comet with a pair of binoculars
    • the orbit was predicted to pass 0.1 AU from Earth
    • became a very bright, naked eye image, brightest comet in 20 years
  • Hale-Bopp
    • discovered in July, 1995
      • simultaneously by Alan Hale in New Mexico and Thomas Bopp in Arizona
    • visible to naked eye in the 1997, one of the brightest comets of the 20th century
      • period is about 4000 years
Stardust Mission
  • Mission launched in February, 1999 to collect cometary material from tail of Comet Wild-2 in January, 2004
  • Will return to Earth in January, 2006

Meteoroids

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  • Meteoroid - chunk of debris before entering Earth's atmosphere
  • Meteor - bright streak in the sky caused by piece of debris
    • "shooting star"
  • Meteorite - a piece of a meteoroid that survives and lands on Earth
  • Meteoroid swarm - fragments from comet that follow same orbit
  • Meteor shower - event where frequent meteors can be seen
Cometary Fragments and Meteor Showers
  • smaller meteoroids are rocky remains of broken up comets
  • certain meteor showers are regular and (fairly) predictable events
Stray Asteroids
  • larger meteoroids (more than a few centimeters) are generally from the asteroid belt
    • responsible for most craters in the inner Solar System
  • Earth is scarred with nearly 100 craters larger than 0.1 km in diameter
  • Major collisions of large meteoroids with the Earth occur every few hundred-thousand years
    • Demise of the dinosaurs 65,000,000 years ago?
    Meteorite Properties
    • Fairly dense: up to 5000 kg/m3 (like asteroids)
    • Most have rocky composition
    • Some are composed mostly of iron and nickel
    • Some show geologic history
      • indicating strong heating sometime in their past, perhaps when they were liberated from a larger body
    • Most are very old (4.4 - 4.6 billion yrs)
    Lunar and Martian Meteorites on Earth
    • Over 30 meteorites have been established as having come to Earth from Mars or the Moon
      • typically billion year old
    • Several are from the Moon

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