ASTR-1010 Planetary Astronomy Day - 34

Course Announcements This Week’s Lab: Comparative Planetology Homework Chapter 9: Due Wednesday April 14. Homework Chapter 10: Due Monday April 19. Homework Chapter 11: Due Friday April 23. Homework Chapter 12: Due Wednesday April 28. Homework Chapter 21: Due Wednesday April 28. -this is extra credit. The last 1 st Quarter moon observing nights are: Tuesday (April 20) & Thursday (April 22) 8:00 pm both nights.

Observations Requirement 1.Attend a 1 st Quarter Observing night Counts 3% of your course grade 2.Do a Virtual Observations Counts 3% of your course grade 3.Write an Observations Report Counts 4% of your course grade Observations total is 10% of your course grade

Virtual Observations See the instructions and list of objects on the handout from the beginning of the semester or Go to APSU Astronomy, click on Observing Nights, click on on campus class, go here then scroll down the page to “Virtual Observation”

How to do the Virtual Observations 1 Install the Starry Night Pro DVD that came with your textbook on your computer or Stay after lab one day and use the laptops in lab to do the assignment You can use Starry Night Pro to find almost all the objects, the named stars and the planets. A few objects will require a web search. Try using the NGC/IC Public Database or do a Google search

How to do the Virtual Observations 2 For planets farther from the sun than Earth use Starry Night Pro 1.Look due south and medium altitude 2.Set the date and time to 9pm January 1 3.Set the time step to 1 day 4.Turn on the planet labels 5.Step forward 1 day at a time and look for when the planet is due south

How to do the Virtual Observations 3 For planets closer to the sun than Earth use Starry Night Pro 1.Look due east on the horizon 2.Set the date and time to 6pm January 1 3.Set the time step to 1 day 4.Turn on the planet labels 5.Step forward 1 day at a time and look for Mercury or Venus. Find when they are highest in the sky 6.Repeat steps 1-5 looking due west

Observations Report Put all the Virtual Observations information into a table that can fit on one or two pages Write up information about telescopes, mounts and observing aids that were discussed at the 1 st Quarter Night. A PowerPoint (also pdf) of the material can be found on the Observing Nights link of Additional information can be found in the So you wanna buy a telescope link. Write up a short description of any celestial objects you viewed at the 1 st Quarter observing night or the Lunar Eclipse night.

Ring Systems All four gas giants have ring systems. Rings are made of swarms of tiny moons. Saturn’s rings are the largest and brightest. The ring particles orbit according to Kepler’s laws. Particle orbits are circular: collisions or ring gravity keep them that way.

Rings of the Giant Planets

Saturn’s Rings A very complicated system, composed of thousands of ringlets. There are bright and dark rings, and “gaps.” Gaps are not empty. Brightness/darkness reflects the amount of material in each ring. The ring system is extremely thin.

Rings and Ringlets NASA/JPL/Caltech

Saturn’s Big Ring

More on Rings The rings do not contain much material. The mass of all the ring particles is about the same as a small, icy moon. Rings can be distorted by the gravity of nearby moons.

Rings and Moons NASA/JPL/Caltech

Origin of the Rings Ring material is from disrupted moons. Large moons cannot orbit close to the planet. Tidal forces from the planet break up close moons. Volcanoes or impacts may also supply the rings. Saturn’s rings formed from an icy moon. Uranus’ and Neptune’s rings are very dark: from a body rich in carbon.

Concept Quiz – Ring Velocities If you could measure the velocities of ring particles at each distance from Saturn, you would find: A.Inner particles orbit at slower speeds. B.Inner particles orbit at faster speeds. C.Orbital speed is the same at all distances.

Moons and Rings Rings don’t last forever. Collisions and sunlight would destroy the rings. Small, nearby shepherd moons can help stabilize the rings. The moons also create gaps. Cause is orbital resonance: orbital period is in a ratio with the moon period.

Large Moons – New Worlds Spacecraft have explored the larger moons. Craters, bright/dark areas reveal geological activity. Some surfaces old, fully cratered. Some surfaces younger: Io, Enceladus, Triton have active volcanoes or geysers. Moons with recent geology must have a source of internal heat.

Internal Heat Tidal forces stretch some moons. As moon orbits, forces change direction. This stretching heats the moon’s interior. Analogy: flexing a paper clip. Io: silicate magma. Enceladus: ice geysers (cryovolcanism). Triton: geysers propelled by nitrogen.

Io NASA/JPL/ Caltech

Concept Quiz – Internal Heat You discover a moon of Jupiter. It orbits very far from the planet, but it has many volcanoes. Is this a surprise? Why? A.No. Any moon can have internal heat. B.Yes. Jupiter is very far from Earth’s Moon. C.Yes. Tidal forces are less for distant moons.

Big Moons G, Titan are larger than Mercury E, C, I, and Triton are larger than Pluto Our Moon is #5, –Between E & I in size Orbit planet in “proper” direction. (mini-SS).

Small Moons Irregular shapes High inclination orbits –Some retrograde Highly elliptical orbits Suggest captured asteroids or KBOs or TNOs Triton

Titan: Possibly Active Titan is Saturn’s largest moon. It has a deep, nitrogen-rich atmosphere. Currently being explored by the Cassini spacecraft. Huygens lander revealed icy “rocks” and a soil rich with organic compounds. Methane in atmosphere renewed by active geology.

Titan NASA/JPL/Space Science Institute

Old Surfaces Most of the larger moons are heavily cratered. As with our Moon, this means no recent geology. Some craters are extremely large. Some moons show fault zones and extensive fracturing; were they caused by large impacts?

Mimas NASA/JPL/Caltech

Life on Galilean Moons Io – extreme tidal heating, no water => no life Callisto – no tidal heating (not in resonant orbit)‏ Ganymede, Europa – tidal heating, but might be a good thing for these.

Europa Liquid water ocean? 1979 – Voyager –Differentiation – water –Smooth surface –Ice covered Galileo s/c – long term monitoring –Subtle variations –Internal structure Galileo spacecraft view

Europa - ocean Lack of impact craters, brittle icy crust? km crust Liquid underneath – gravitometer measurements 1996 – magnetic field – opposes Jupiter's

Chaotic terrain Recent water breakout?

Evidence for Ocean Small number of craters – young surface Surface features – suggest water from below Magnetic field – something conducts electricity Tidal heating supplies enough heat to melt ice. Proof will have to wait: Europa mission –Long-wave radar –Laser altimeter

Life on Europa 3 key elements for life –Source of elements/molecules to build living organisms –Source of energy for metabolism & growth –Liquid medium for transporting molecules Good, indirect evidence of liquid water ocean. Expect elements for life in ocean and on floor. Possible energy sources, but small wrt Earth.

Energy question But, how do you use it? To use warm water energy, you have to have a cold sink. How wide spread could life be? –On Earth, very little life derives its energy & material directly from volcanic vents.

Ganymede Largest in solar system Has old and young surfaces Intrinsic magnetic field Variation of field with Jupiter rotation – liquid High-density ice forms

Types of Ice

Callisto Farthest out of the four. Old surface. Evidence of ice sublimation (powder)‏ Magnetic field – ocean? Much less energy

Saturn & Beyond Titan –2 nd largest moon in SS –Thick atmosphere 1.5 X Earth pressure –Cold -180C –90% Nitrogen, 0 Oxygen –Methane, Argon, Ethane –Lower impact velocities

Cassini - Huygens Coastline-like features No pooling of liquids Huygens landing site – dry Cassini – evidence of lakes & rivers

Cassini - Huygens Cassini – evidence of lakes & rivers Liquid methane lakes near pole? Wind blown dunes?

Life on Titan? Solid ice, no liquid water Other liquid hydrocarbons (methane)‏ –Slower chemical reaction rates UV produces a lot of organic molecules in the atmosphere. These should settle out and build on the surface. Energy sources? –Cryovolcanoes? –Acetylene reactions

Enceladus Several of Saturn's moons show evidence of past geological activity. Enceladus - current activity. Fresh ice Ice spray – water? Subsurface ocean –ammonia/water mix Tidal heating

Triton Backwards orbit –Suggests captured KBO Resurfacing actions Internal heat source –Tidal heating –Radioactive decay? Cryovolcano activity

Uranus has thin rings and several moons

The Moons of Uranus