Astronomy 1010 Planetary Astronomy Fall_2015 Day-38

TNO_Wide-1

Course Announcements SW-chapter 11, 12 due: Mon. Dec. 7 1 st Thursday Art Walk – 5-8pm on Study Day This week is the make-up week for labs … We will have the equipment for Lenses & Telescopes and the Spectrometer set up. These are the only two that will be setup in lab. Any other labs (computer based) must be completed PRIOR to Tuesday. I will have a substitute for the cratering lab for those that need it.

Ring Systems  All four gas giants have ring systems.  Saturn’s rings are the largest and brightest.  The fainter rings were discovered by stellar occultation methods.

 A very complicated system, composed of thousands of ringlets, each made up of tiny orbiting particles that obey Kepler’s laws.  There are bright and dark rings, “gaps,” and divisions.

 The moons obey Kepler’s laws as they orbit the planet:  For a particular planet, the left-hand side will be a constant for most of its moons.  For Jupiter, Ganymede, Europa, and Io are in an orbital resonance of 1:2:4.  Can estimate relative orbital distance. MATH TOOLS 11.1

 Gaps are not empty.  Brightness/darkness reflects the amount of material in each ring.  Though wide, the ring system is extremely thin.  If Saturn were a basketball, a piece of paper is >1,000 times too thick.

 Diffuse rings are fainter and have no defined boundaries.  Saturn’s largest ring is a diffuse dust ring, discovered in  E Ring and G Ring are also diffuse.

 The rings of the other giant planets are mostly narrow and diffuse.  Backlighting brings them into view.  Neptune has denser sections known as ring arcs.

 Ring particles are from disrupted moons or from volcanic activity on moons.  Saturn: bright rings because they are made of water ice.  The total mass of Saturn’s bright rings is about the same as a small icy moon.  Uranus and Neptune: dark rings from organic material (darker than coal).  Jupiter: not as dark as the ice giants, nor as bright as Saturn’s; most likely composed of dark silicates.

 Rings are kept stable by shepherd moons.  Shepherd moons can also distort rings.  Gravity can cause distortions, including what look like twists and waves.

 Other distortions include scalloped shapes and appearance of transient spokes in Saturn’s rings.

 Rings do not last forever.  Collisions and sunlight destroy rings.  Shepherd moons can help stabilize rings.  Orbital resonances can create gaps.  Earth does not have a ring because it lacks shepherd moons to contain the material.

i_Clicker Question Jovian Planets: Saturn Ring Gaps Jovian Planets: Shepherd Moons

 The tidal force between a planet and its moon depends on their masses, the size of the moon, and the distance between them:  Can use this to find the relative tidal forces for different moons of the same planet. MATH TOOLS 11.2

 The moons of the giant planets have a much lower escape velocity than that of Earth, which is 11.2 km/s or >40,000 km/h.  Cannot easily hold on to particles ejected during volcanic activity.  Enceladus:  Its cryovolcanic plumes are nearly 2,200 km/h. MATH TOOLS 11.3

 The identification of extremophile bacteria on Earth has led to consideration of the possibility of life in the extreme environments of the Solar System’s moons.  The combination of liquid water, heat, and organic compounds could be present.  Enceladus, Europa, Titan, and Callisto are possibilities for life.

 Small particles are best viewed when they are between the observer and light source.  Backlighting allows for the rings of the planets to be viewed most easily.  Most light that hits the particles still comes to the observer instead of being scattered away. CONNECTIONS 11.1

 Apparent violations of well-supported theories are exciting for scientists because they must be reconciled.  This often means that something new is about to be discovered. PROCESS OF SCIENCE

 Planetesimals left over from the formation of the solar system include asteroids and comets, as well as meteorites and meteroids.  Five large planetesimals deserve their own classification: dwarf planets.  Four reside in the Kuiper Belt beyond Neptune’s orbit: Pluto, Haumea, Makemake, and Eris.  Ceres is in the main asteroid belt.

 Pluto is about 1/400 the mass of Earth.  “Double planet”: Pluto/Charon.  Eccentric orbit.  Rock and ice.  Thin methane atmosphere.

 Eris, larger than Pluto, is the most distant.  Has moon, Dysnomia.  Orbit has greater inclination than Pluto’s.  Ceres used to be known as the largest asteroid.  Spherical, about 4% the mass of the Moon.