Download Uranus and Neptune

Uranus and Neptune
• Uranus: general information
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Discovered in 1781 (Herschel)
Radius about 4x that of Earth
Mass about 14.5x that of Earth
Nearly featureless atmosphere
Thin, dark rings
27 moons
(Voyager 2, NASA/JPL)
• Neptune: general information
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Discovered in 1846
Radius about 4x that of Earth
Mass about 17x that of Earth
Has internal heat & an active
atmosphere
– 13 moons
(Voyager 2, NASA/JPL)
Uranus and Neptune
• Uranus and Neptune have nearly identical sizes and
internal structures
• Both appear bluish-green in color
– Sunlight passes through an
outer haze layer and reflects off
the cloud tops below
– The haze is rich in methane,
which strongly absorbs red and
orange light, letting blue and
green light pass through
• This bluish-green light is what gets
reflected by the clouds below
– An additional factor is blue-light
scattering in the haze layer
(Neptune & Triton, Voyager 2, NASA/JPL)
Spacecraft Visits
• Voyager 2 fly-bys
– Uranus: January 1986
– Neptune: August 1989
• Hubble Space Telescope studies
– Long-term monitoring of atmospheric weather patterns
– Infrared imaging studies of their atmospheres, rings, and
moons
(HST image of
Neptune and its
largest moon Triton,
NASA/JPL)
Orbit and Rotation of Uranus
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Average distance from Sun: 19.2 AU
Orbital period: 84 years
Orbital eccentricity e = 0.05
Rotation axis tilted by about 980
– Tilted on its side in its orbital plane
– Because intensity of sunlight is so weak
at Uranus, and since interior of Uranus (copyright Calvin J. Hamilton)
is a good insulator (holding heat), this
has little effect on seasonal temperature variations
Uranus
Sun
Orbit and Rotation of Neptune
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Average distance from Sun: 30.1 AU
Orbital period: 165 years
Orbital eccentricity e = 0.01 (nearly circular)
Rotation axis tilted by 300
– Similar to Earth, Mars, and Saturn
– Has seasonal pattern of solar heating similar to Earth’s
• Rotational period: 16.1 hours
– Has significant magnetic field
– Similar to Uranus
(copyright Calvin J. Hamilton)
Interiors of Uranus and Neptune
• Interior structures of both planets are very similar
• Atmosphere composition: molecular hydrogen (H2), Helium
(He), and methane (CH4)
• Thick, slushy mantle of water, ammonia, and methane ices
• Rocky cores about the size of Earth
• Both planets lack the deep metallic hydrogen mantles found
on Jupiter and Saturn because of their smaller size (pressure
doesn’t get large enough)
Atmosphere of Uranus
• Uranus appears as a virtually featureless hazy
bluish-green ball
– The reason is a lack of internal heat, unlike the other gas
giants
– There is a lack of convection in the atmosphere  maybe
due to layered interior (like an onion)…?
– Clouds are cold and don’t billow up above the top layer of
haze
– Results in a generally uniform appearance
– Occasional clouds/storms
seen by HST in the infrared
(Voyager 2, NASA/JPL)
Atmosphere of Uranus
(NASA/JPL)
Atmosphere of Neptune
• Neptune, like Jupiter and Saturn, radiates about
2.7x as much energy as it receives from the Sun
– Creates atmospheric convection and weather on Neptune
• Belts and bright clouds of methane ice
• Dark oval cyclonic storms
(NASA/JPL)
Atmosphere of Neptune
(Voyager 2, NASA/JPL)
Atmosphere of Neptune: Great Dark Spot
• Large storm that
appeared in the mid1980s and then
vanished by 1995
(Voyager 2, NASA/JPL)
Neptune’s Great Dark Spot
(Voyager 2, NASA/JPL)
Rings of Uranus
(Voyager 2, NASA/JPL, copyright Calvin J. Hamilton)
Rings of Uranus
(Voyager 2, NASA/JPL)
Rings of Uranus
(Voyager 2, NASA/JPL)
Rings of Neptune
(Voyager 2, NASA/JPL)
Rings of Neptune
(Voyager 2, NASA/JPL)
Pluto
• General information
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Discovered in 1930 (Tombaugh)
Only planet not visited by a spacecraft
Receives only 1/1600th the sunlight received by Earth
Surface temperature of 35–45 K (–378 to –396 0F)
Density suggests a rocky core surrounded by an icy
mantle
– Very tenuous CH4 atmosphere
• Surface pressure is 100,000x smaller than Earth’s
– Surface is covered with frozen N2 mixed with CH4 and
traces of CO and H2O
Orbit and Rotation of Pluto
• Average distance from Sun: 39.5 AU
• Orbital period: 248.5 years
• Orbital eccentricity e = 0.25 (largest of the
planets)
– Closer to the Sun than Neptune for 20 years out
of its orbit around the Sun
• Orbital inclination: 170
• Rotation axis tilted by
about 1200
– Affects views from Earth
strongly
(www.nineplanets.org)
(copyright Calvin J. Hamilton)
Charon
• Pluto has one large moon: Charon
– Discovered in 1978 (Naval Observatory)
– Largest moon/planet size ratio in the solar system (radius
of 625 km for Charon vs. 1150 km for Pluto)
• Pluto and Charon experience synchronous rotation
with each other
– Always keep the same face toward each other
(HST, NASA/JPL)
Pluto and Charon Size Comparison
Pluto
Charon
Surface of Pluto
(HST, NASA/JPL, ESA)
NASA’s New Horizons Mission
• Launched in January 2006
• Scheduled for Pluto fly-by (first ever) in 2015
• Will be followed by encounters with objects in the
distant Kuiper Belt (about 50 AU from Sun) in 2016
– 2020
• See the following website for mission details:
pluto.jhuapl.edu/