ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day - 34

Course AnnouncementsCourse AnnouncementsThis 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 1st Quarter moon observing nights are:

Tuesday (April 20) & Thursday (April 22)

8:00 pm both nights.

Observations RequirementObservations Requirement1. Attend a 1st Quarter Observing night

Counts 3% of your course grade

2. Do a Virtual ObservationsCounts 3% of your course grade

3. Write an Observations ReportCounts 4% of your course grade

Observations total is 10% of your course grade

Virtual ObservationsVirtual ObservationsSee the instructions and list of objects on the handout from the beginning of the semester

orGo 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 theHow to do theVirtual Observations 1Virtual Observations 1

Install the Starry Night Pro DVD that came with your textbook on your computer

orStay 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 theHow to do theVirtual Observations 2Virtual 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 theHow to do theVirtual Observations 3Virtual Observations 3

For planets closer to the sun than Earth use Starry Night Pro

1. Look due east on the horizon2. Set the date and time to 6pm January

13. Set the time step to 1 day4. Turn on the planet labels5. 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 ReportObservations 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 1st Quarter Night. A PowerPoint (also pdf) of the material can be found on the Observing Nights link of www.apsu.edu/astronomy Additional information can be found in theSo you wanna buy a telescope link.

•Write up a short description of any celestial objects you viewed at the 1st Quarter observing night or the Lunar Eclipse night.

Ring SystemsRing 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 Rings of the Giant PlanetsGiant Planets

Saturn’s RingsSaturn’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 Rings and RingletsRinglets

NASA/JPL/Caltech

NASA/JPL/Caltech

Saturn’s Big RingSaturn’s Big Ring

More on RingsMore 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 MoonsRings and Moons

NASA/JPL/Caltech

Origin of the RingsOrigin 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 VelocitiesConcept 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 RingsMoons 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 WorldsLarge 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 HeatInternal 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.

IoIo

NASA/JPL/Caltech

Concept Quiz – Internal HeatConcept 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 MoonsBig 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 MoonsSmall Moons• Irregular shapes

• High inclination orbits– Some retrograde

• Highly elliptical orbits

• Suggest captured asteroids or KBOs or TNOs

• Triton

Titan: Possibly ActiveTitan: 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.

TitanTitan

NASA/JPL/Space Science Institute

Old SurfacesOld 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?

MimasMimas

NASA/JPL/Caltech

Life on Galilean MoonsLife 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.

EuropaEuropa • 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 - Europa - oceanocean

• Lack of impact craters, brittle icy crust?• 80-170 km crust• Liquid underneath – gravitometer measurements• 1996 – magnetic field – opposes Jupiter's

Chaotic terrain

Recent water breakout?

Evidence for OceanEvidence 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 EuropaLife 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 questionEnergy 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.

GanymedeGanymede • 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 IceTypes of Ice

CallistoCallisto

• Farthest out of the four.

• Old surface.

• Evidence of ice sublimation (powder)

• Magnetic field – ocean?

• Much less energy

Saturn & BeyondSaturn & Beyond• Titan

– 2nd largest moon in SS– Thick atmosphere

• 1.5 X Earth pressure– Cold -180C– 90% Nitrogen, 0 Oxygen– Methane, Argon, Ethane– Lower impact velocities

Cassini - HuygensCassini - Huygens

Coastline-like featuresNo pooling of liquids Huygens landing site – dryCassini – evidence of

lakes & rivers

Cassini - HuygensCassini - Huygens

Cassini – evidence of lakes & riversLiquid methane lakes near pole?

Wind blown dunes?

Life on Titan?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

EnceladusEnceladus• 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

TritonTriton• Backwards orbit

– Suggests captured KBO

• Resurfacing actions• Internal heat source

– Tidal heating– Radioactive decay?

• Cryovolcano activity

Uranus has thin rings and Uranus has thin rings and several moonsseveral moons

The Moons of UranusThe Moons of Uranus