Transcript 1. Great Dark Spot

1. Great Dark Spot
• A hurricane-like storm on Neptune. It is
Earth-size and similar to Jupiter’s Great Red
Spot.
2. perturbation theory
• The mathematics that explains how the orbit
of one celestial body would be affected by
the attraction of a third celestial body.
3. radiation darkening
• High-energy bodies striking the surface of a
moon can break up molecules; leading to
chemical reactions whose products are dark,
organic materials. This might explain the
low albedo of the moons of Uranus and
Neptune.
4. stellar occultation • When an object blocks the light of a bright
star, dimming the star’s light.
• A stellar occultation by Uranus in 1977
resulted in the discovery of its rings (the
first seen since Saturn’s).
1. How was Uranus discovered?
• Uranus was discovered by William Herschel
in 1781. He first thought it was a comet,
but it moved too slowly.
• It was the first new planet discovered in
over 2000 years.
2. Why did astronomers suspect
an eighth planet beyond Uranus?
• No elliptical orbit fit the orbit of Uranus.
Astronomers concluded the only explanation
was that another object was attracting
Uranus.
3. What is the most unusual
feature about the rotation of
Uranus?
• Uranus’ rotation axis lies IN the ecliptic
plane.
• It appears as though Uranus is lying on its
side.
• Uranus exhibits differential rotation, but it
rotates faster at the poles than at the equator.
4. Why do Uranus and Neptune
have a bluish color?
• There is more methane in the atmosphere.
Methane absorbs red light.
5. How are the interiors of
Uranus and Neptune thought to
differ from those of Jupiter and
Saturn?
• Uranus and Neptune are denser than Saturn
and Jupiter, so their rocky cores must make
up a greater percentage of the planet. The
rocky cores of all the Jovian planets are
about the size of Earth.
6. Name an unusual feature of
the winds on Neptune.
• The zonal wind flow is retrograde to the
planet’s rotation.
• The surface winds have speeds of over 2000
km/hr.
7. What is so unusual about the
magnetic fields of Uranus and
Neptune?
° The magnetic fields are tilted from 60 to 46
degrees from the rotational axis. They are
also offset from the center of the planets.
8. What observation weakens the
idea that the sideways rotation of
Uranus was caused by a
catastrophic event?
• The moons are all similar, indicating they
were not captured. But they orbit in the
rotational plane; what catastrophic event
could have also tilted the moon’s orbits
without expelling them from their orbits?
9. What is unique about
Miranda?
• A wide range of surface terrains. It appears
that Miranda has been catastrophically
disrupted several times, with gravity pulling
the pieces together in a jumbled, chaotic
way.
10. How does Neptune’s system
of moons differ from those of
other Jovian worlds?
• Neptune is the only Jovian planet without a
regular moon system.
• Triton is the only large moon in the solar
system with a retrograde orbit.
• Nereid has a tremendously elongated orbit
(1.4 million km to 9.7 million km).
11. What is the predicted fate of
Triton?
• Triton’s tidal bulge and retrograde orbit
cause it to spiral toward Neptune. In about
100 million years Triton will move within
Neptune’s Roche Limit and it will be torn
apart by gravitational forces and the
remains will form a ring.
12. How do the rings of Uranus
differ from the rings of Saturn?
• They are much darker. They are about the
same thickness. They have shepherd
satellites.
13. How do the rings of Neptune
differ from those of Uranus and
Saturn?
• Neptune has four primary rings.
• They are darker than Saturn’s.
14. How was Pluto discovered?
• Neptune and Uranus seemed to be further
perturbed by another object. Scientists
calculated where this object should be in the
sky and concentrated their observations
there. It was discovered by Clyde
Tombaugh in 1930.
15. How were the masses and
radii of Pluto and Charon
determined?
• By observing a series of Pluto-Charon
eclipses from 1985 to 1991.
16. In what respect is Pluto more
like a moon than like a Jovian or
terrestrial planet?
• Pluto is much smaller than any other planet.
• It is barely larger than half the size of the
United States.
• Pluto is similar in mass and size to Triton
(Neptune’s moon).