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Transcript
Chapter 13: The Outer Solar System
Uranus Visuals
uranus3.jpg
Neptune Visuals
neptune.jpg
Neptune_Full.jpg
vital statistics
Orbital distance (AU)
Orbital period
(Yrs)
Rotation period
Axial tilt
Known Satellites
Mass
(xMEarth)
Radius
(xREarth)
Density
Surface Gravity
Global Temp
Escape Velocity
(km/s)
(earth’s 11.2 km/s)
Uranus
19.2
84.0
17.2 hrs
98º
15
14.5
Neptune
30.1
164.8
16.1 hrs
30º
8
17.1
4.0
3.9
1.3
.91 g
60 K
21
1.6
1.19 g
60 K
23
1
[See also tables 13.1, 2]
Discovery
Uranus
visible with naked eye(faint)
discovered in 1781 by William Hershel during a study of visible
stars. (“accidental”)
Neptune
existence deduced from perturbations in Uranus’s orbit
calculation (+ luck/assumptions)
→ predicted positions by Couch and Leverrier ~1846
→ observed location by Galle ~1846
2
Uranus [figure 13.2,4] and Neptune [figure 13.6-8]
Gas giants with ring systems
Neptune: small axial tilt
Uranus: severe axial tilt (~ 98º) [figure 13.1,13_2.mov]
Atmospheres [figure 13.5]
methane gives blue coloring
Uranus:
featureless
Hydrogen and Helium: Solar Mix
no atmospheric convection
Neptune
clouds and storms
Great Dark Spot
belts and zones from convection
3
Uranus and Neptune (cont’d)
Interiors: [Figure 13.9]
Rocky cores
Water, molten rock
Gas exterior (mostly hydrogen, helium)
Internal Energy
Uranus: essentially no excess heat radiated
“insulated” by suppressed convection?
Neptune: ~60% radiated energy (“self-luminous”)
from internal heat
Magnetospheres [Figure 13.10]
no large metallic hydrogen core
fields not aligned with axis of rotation
center of fields not at center of planet
probably generated in icy fluid region outside of rocky core
4
Uranus and Neptune (cont’d)
Rings:
Uranus [figure 13.12, 14 ]
discovered during stellar occultation [figure 13.11]
narrow rings of large particles (w/ shepherd moons) [fig 13.15]
+ dust in regions between rings
Neptune [figure 13.16-18 ]
2 thin rings + broad inner ring, all made of microscopic
particles
5
Trans-Neptunian Objects (TNO's)
Pluto (and Charon) [figure 13.23, Plutoids.jpg]
Pluto's discovery:
additional perturbations of Uranus’s orbit → prediction by Lowell ~ 1905
Pluto found much smaller than predicted, via photographs ~ 1930
[discovering_pluto.jpg]
reclassified 2006 as dwarf planet
orbit “crosses” Neptune’s orbit [Figure 13.19]
orbital resonance makes + geometry makes collision impossible
mass (of Pluto + Charon) ~ 1/6 Earth’s moon
eclipses + intensity variation to map surface [Fig 13.20,21]
determine sizes
Pluto’s radius ~ 2300 km, Charon ~ 1200 km
=> density ~ 2 x water => not just icy materials
thin atmosphere
icy surface (highly reflective)
6
Other TNOs
No large planets discovered beyond Neptune
Over 1200 TNOs discovered [TheTransneptunians_73AU.svg.png]
possibly over one million TNOs with diameters larger than tens of kilometers
Large TNOs [EightTNOs.png]
Eris: larger than Pluto!
Kuiper Belt Objects (KBOs)
Icy bodies
Circular orbits near plane of solar system
Resonant KBOs trapped in resonance with Neptune
Scattered Disk Objects (includes Eris)
Larger, more eccentric and more inclined orbits
Centaur objects: already “encountered” Neptune, closer orbits, “doomed”
Possible history of the solar system [figure 13.24]
7
Redefining Pluto
Planet: orbits the sun, massive enough to have spherical shape, dominates neighborhood
(clearing of other objects)
Dwarf Planet: orbits the sun, massive enough to have spherical shape
TNO's Pluto, Eris, Haumea and Makemake plus non-TNO Ceres
2000px-Solar_System_size_to_scale.svg.png
8