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Explore the intricate details of Saturn's rings, moons, and other celestial phenomena like Uranus and Neptune. Uncover the mysteries of ring formation, moon interactions, and unique characteristics of each planet. Witness the beauty and complexity of our outer solar system.
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October 5, 2011 – 10am class Today: Saturn, Uranus, Neptune, Pluto, Kuiper Belt, Comets
Saturn and its moons Photo taken by Cassini Spacecraft
Orbital period = 29.5 Earth years So as we go around the Sun, we see the rings with different tilts
Saturn’s Rings • Very thin – 10-20 METERS thick • Icy particles (water ice) 1cm – 5m • Rings were once thought to be moons which are inside the “Roche limit” • Cassini’s divisions: Gaps in the rings, caused by resonances with the moons of Saturn Earth-based Telescope picture of Saturn
Roche Limit A large moon can be torn apart by the “tidal” forces of the planet: The gravity near the planet is larger than the gravity on the far side of the moon, away from the planet When this tidal force is greater than the self-gravity of the moon, the moon disintegrates
Artist’s Conception of Rings Close-Up Snowflakes to Boulders
Gap Moons • Some small moons create gaps within rings.
Shepherd Moons • A pair of small moons can force particles into a narrow ring.
Resonance Gaps • Orbital resonance with a larger moon can also produce a gap.
Jovian Ring Systems • All four jovian planets have ring systems. • Others have smaller, darker ring particles than Saturn.
Why do the jovian planets have rings? • They formed from dust created in impacts on moons orbiting those planets. How do we know?
How do we know? • Rings aren’t leftover from planet formation because the particles are too small to have survived for so long. • The ring particles are constantly ground down by collisions with other ring particles and micrometeorites, and then swept into the planet by the pressure of light • There must be a continuous replacement of tiny particles. • The most likely source is impacts with jovian moons.
Ring Formation • Jovian planets all have rings because they possess many small moons close in. • Impacts on these moons are random. • Saturn’s incredible rings may be an “accident” of our time.
What have we learned? • What are Saturn’s rings like? • They are made up of countless individual ice particles. • They are extremely thin with many gaps. • How do other jovian ring systems compare to Saturn’s? • The other jovian planets have much fainter ring systems with smaller, darker, less numerous particles. • Why do the jovian planets have rings? • Ring particles are probably debris from moons.
Saturn’s Moons • Titan: • Only moon in the solar system with an atmosphere • 1.5x pressure of the Earth’s atmosphere
Titan’s Atmosphere • Titan is the only moon in the solar system to have a thick atmosphere. • It consists mostly of nitrogen with some argon, methane, and ethane. • ethane is a greenhouse gas Titan is warmer than it would be without ethane but still 180C
Titan’s Surface • Huygens probe provided first look at Titan’s surface in early 2005. • It found liquid methane and “rocks” made of ice.
Medium Moons of Saturn • Almost all of them show evidence of past volcanism and/or tectonics.
Medium Moons of Saturn • Ice fountains of Enceladus suggest it may have a subsurface ocean.
Aurorae on Saturn Probably debris from moons, not solar wind excite Saturn’s aurorae
Uranus and Neptune • Uranus was discovered in March 1781 by William Herschel and was the first planet discovered with a telescope • Neptune was discovered in 1846, after astronomers Adams and Leverrier predicted its existence, based on irregularities in Uranus’ orbit • Uranus and Neptune are similar in size, composition and internal structure • Both Uranus and Neptune appear bluish because of methane in their atmosphere
Uranus • The only spacecraft to visit Uranus was Voyager 2 in 1986 • Uranus’ rotational axis is tilted by 90 degrees probably the result of a really big collision • Uranus’ magnetic field is tilted 60 degrees with respect to its rotational axis
SEASONS on Uranus are EXTREME: • Winter solstice (which last occurred in 1985 AD): • The north pole is pointed almost directly away from the Sun. • The northern hemisphere experiences perpetual darkness. • The southern hemisphere experiences perpetual sunlight. • Spring equinox (2006 AD): • The rotation axis is perpendicular to the Uranus-Sun direction. • From any point on Uranus, the Sun rises in the east and sets in the west 8 1/2 hours later. • Summer solstice (2027 AD): • The north pole is pointed almost directly toward the Sun. • The north experiences perpetual sunlight. • The south experiences perpetual darkness
Neptune Has a big storm, Similar to Jupiter’s Big Red Spot
Neptune’s biggest moon is Triton: (picture from Voyager 1989)
Triton: Retrograde, inclined orbit - captured? 38 oK