Uranus
and Neptune
Printable
version
April
25, 2000
Announcements
Uranus
and Neptune Preview
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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Uranus
overview (Jovian planet)
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Neptune
overview (Jovian planet)
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Discovery
of Uranus
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Discovery
of Neptune
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Triumph
of Newtonian mechanics
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Seeing
Uranus and Neptune from Earth
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Uranus
form Voyager 2
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Featurless
upper atmosphere
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weird
rotation axis tilt
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composition
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Neptune
from Voyager 2
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More
active upper atmosphere
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more
normal rotation axis tilt
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Uranus
and Neptune possible internal structure
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Unsolved
puzzles
Uranus
overview
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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5 AU,
10 AU, 20 AU, 30
AU, 40 AU
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Differential rotation
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inside slower than outside
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poles slower than equator
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Orbital period ~ one lifetime
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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5 AU,
10 AU, 20 AU, 30
AU, 40 AU
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Differential rotation
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What 4 other Solar system
bodies exhibit differential rotation?
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Uranus,
Saturn, Jupiter, Sun
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Orbital period ~ two lifetimes
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Same size as Uranus, but
heavier
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Uranus: 14.5 Earth Masses
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Neptune: 17.2 Earth Masses
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Which planet is denser?
Discovery
of Uranus
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Jupiter,
Saturn, Uranus,
Neptune, Pluto
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William
Herschel, 1781 doing a sky survey
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noticed
something fuzzy
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initially
thought a comet
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moved
like a planet in a large orbit
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phrase
of scientific discovery is usually not "Eureka" but "Hmm, that's funny"
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Uranus
had been charted as a star as early as 1690
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moves
4 degrees every year
Discovery
of Neptune
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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Uranus
wasn't moving as expected
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1843
John Couch Adams used discrepancy to predict position of undiscovered planet
(Neptune)
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1845
Le Verrier made same calculation
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predicted
position within 1 degree of Adams'
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English
observers hesitant to look for planet because didn't have a good map of
that part of the sky
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Le
Verrier gave predicted position to Berlin observatory
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Had
good maps
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found
Neptune in one night
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In
1613, Galileo probably saw it while observing Jupiter
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didn't
pay much attention to it
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Jupiter
moved past Neptune, Neptune was "lost" for 200 years
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Neptune
moves only 2 degrees per year
Seeing
Uranus and Neptune from Earth
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Not naked eye objects
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Need a good, big telescope
Uranus
from Voyager 2
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Jupiter,
Saturn, Uranus,
Neptune, Pluto
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Uranus
upper atmosphere almost featureless even from Voyager
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Rotation
axis tilted nearly into plain of orbit around Sun!
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98
degree tilt
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net
rotation is retrograde (backwards)
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probably
rotating normally, then hit by something
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what
other planet (that we've learned about so far) has retrograde rotation
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LONG
seasons (~20 years)
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84%
hydrogen, 14% helium, 2% methane
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methane
absorbs reds and yellows
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why
Uranus is greenish blue
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Unlike
Jupiter and Saturn, there is no ammonia (NH3) in Uranus's upper
atmosphere
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Uranus
upper atmosphere temperature is 55K
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ammonia
is frozen, rains down to bottom of atmosphere
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probably
why no water either
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A similar
mechanism may have depleted Helium in the outer atmosphere of what planet?
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ammonia
and water are important constituents of the clouds of what planets?
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Upper
atmosphere winds move west to east (like rotation)
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No
zonal winds like Jupiter or Saturn
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Temperatures
in winter similar at poles and equator (at top of atmosphere)
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must
have good circulation
Neptune
from Voyager 2
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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Neptune
more dense
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Has
internal heat source
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may
still be contracting from formation
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upper
atmosphere temperature 55 K
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30
degree tilt of rotational axis
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84%
hydrogen, 14% helium, 2% methane (same as Uranus)
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No
water, no ammonia
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what
color is Neptune?
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Has
clouds, storms
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clouds
may be frozen methane
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great
dark spot in southern hemisphere
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there
in 1989, gone in 1994
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new
storm in northern hemisphere in 1995\
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Has
some belts and zones
Neptune,
cloud close up
Belts
and Zones in Neptune (data from Larry Sromovsky of UW)
Internal
structure
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
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Internal
structure not precisely known
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rocky
core almost certain
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outer
atmosphere known
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the
rest is calculated
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how
do we know about the internal structure of the Earth?
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Seismic
waves (Earthquakes)
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Magnetic
fields of Uranus and Neptune not centered nicely
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tilted
at large angles relative to rotation axis
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moving
electric charges cause magnetic fields
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charges
exist in:
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Earth:
liquid iron
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Jupiter
and Saturn: liquid metallic hydrogen
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Uranus
and Neptune: ions in water?
Unsolved
Puzzles
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Jupiter,
Saturn, Uranus, Neptune,
Pluto
-
Why
is Uranus tilted so much?
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Why
are there more heavy elements in Uranus and Neptune
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What
causes their misaligned magnetic fields?
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What
is Neptune's heat source?
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One
possible cause for all of these:
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Uranus
and Neptune formed closer to the sun and were thrown out by large impacts
Uranus
and Neptune Summary
-
Jupiter,
Saturn, Uranus, Neptune,
Pluto
-
Uranus
overview (Jovian planet)
-
Neptune
overview (Jovian planet)
-
Discovery
of Uranus
-
Discovery
of Neptune
-
Triumph
of Newtonian mechanics
-
Seeing
Uranus and Neptune from Earth
-
Uranus
form Voyager 2
-
Featureless
upper atmosphere
-
weird
rotation axis tilt
-
composition
-
Neptune
from Voyager 2
-
More
active upper atmosphere
-
more
normal rotation axis tilt
-
Uranus
and Neptune possible internal structure
-
Unsolved
puzzles