ASTR-1010ASTR-1010Planetary AstronomyPlanetary Astronomy

Day - 25

AnnouncementsAnnouncementsSmartworks Chapter 9-12: Due Tuesday, Dec. 14 @1030 am

Final Exam: 1030-1230 Tuesday Dec. 14

Visit to the Observatory & Virtual Observations Reports due Tuesday Dec. 7!due Tuesday Dec. 7!

Last chance for bonus points:

PHYS-1234 class – Thursday 4:00pm – E106B

Dr. Susana Deustua – STScI – “Looking at Dust's Effect on Type Ia Supernovae Measurements”

Ring SystemsRing 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.

Saturn’s RingsSaturn’s Rings

• Ring particles obey Kepler’s Laws

• A very complicated system, composed of thousands of ringlets.

• There are bright and dark rings, “gaps,” and divisions.

Saturn’s RingsSaturn’s Rings• Gaps are not empty.

• Brightness/darkness reflects the amount of material in each ring.

• Though wide, the ring system is extremely thin.

Saturn’s Big RingSaturn’s Big Ring

Rings of the Other GiantsRings of the Other Giants

• Mostly narrow and diffuse.

• Backlighting brings them into view.

• Neptune has denser sections known as ring arcs.

More on RingsMore on Rings

• Ring particles are from disrupted moons or from volcanic activity on moons.

• Saturn: bright rings because they are made of water ice.

• 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.

Gravitational DistortionGravitational Distortion

• Shepherd moons that help keep the rings crisp can also distort them.

• Gravity can causes distortions including what look like twists and waves.

Ring StabilityRing Stability

• Rings do not last forever.

• Collisions and sunlight destroy the rings.

• Shepherd moons can help stabilize the rings.

• Orbital resonances can create gaps.

• Earth does not have a ring because it lacks shepherd moons to contain the material.

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.

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.

Concept Quiz – Moons and Concept Quiz – Moons and RingsRings

You discover a moon of Saturn in a gap of its rings. The moon

most likely …

A. Recently accreted from ring material.

B. Maintains the gap due to its gravitational influence.

C. Is not the reason for the “twists” in nearby rings.

D. Is a figment of your imagination; the gaps are completely empty.

This concludes the Lecture PowerPoint presentation This concludes the Lecture PowerPoint presentation for Chapter 11for Chapter 11

©2010 W.W. Norton & Company, Inc.

For more learning resources, please visit the StudySpace website for 21st Century Astronomy athttp://wwnorton.com/studyspace

21st CENTURY ASTRONOMY

THIRD EDITIONHester | Smith | Blumenthal | Kay | Voss

Chapter 12Chapter 12Lecture OutlineLecture Outline

Dwarf Planets and Small Solar Dwarf Planets and Small Solar System BodiesSystem Bodies

Dwarf PlanetsDwarf Planets

• Five large planetesimals left over from the formation of the Solar System.

• Four reside in the Kuiper Belt beyond Neptune’s orbit: Pluto, Haumea, Makemake, and Eris.

• One is in the main asteroid belt: Ceres.

PlutoPluto

• Very small – 1/6 the mass of Earth’s Moon.

• Binary planet: Pluto/Charon.

• Has properties like comets:– Eccentric orbit– Icy composition (probably)

• Member of the Kuiper Belt Objects, maybe not even the largest one.

PlutoPluto• About 1/400 the

mass of Earth

• Double planet: Pluto/Charon

• Eccentric orbit

• Rock and ice

• Thin methane atmosphere

Pluto & Charon are not bigPluto & Charon are not big

Pluto and Charon Eclipsed

each other from 1985-

1990

Like Uranus, Pluto orbits on its side

Pluto Has An Atmosphere!

Pluto is covered in Methane Frost

All is speculation until the New All is speculation until the New Horizons mission arrives in Horizons mission arrives in

20162016

Other Dwarf PlanetsOther Dwarf Planets

• Eris is the most distant, larger than Pluto but similar.

• Ceres used to be known as the largest asteroid.

• Spherical, about 4% the mass of the Moon.

Asteroids and CometsAsteroids and Comets• Asteroids and comets are relics of the early

Solar System.

• Asteroids: rocky, in between Mars and Jupiter.

• Comets: icy, beyond the planets.

Asteroids and MeteoritesAsteroids and Meteorites

• Meteorites are pieces of asteroids that have fallen to Earth.

• In space a meteorite is called a meteoroid.• While passing through the atmosphere, it is a meteor.

Types of MeteoritesTypes of Meteorites

• Over 90% are stony, like Earth rocks.• Can have round chondrules (chondrites) or not

(achondrites), and some have carbon.• Can use meteorites to date the age of the Solar

System (4.5 billion years).

Types of MeteoritesTypes of Meteorites

• Iron meteorites have high concentrations of metal, with a melted and pitted appearance.

• Stony-iron meteorites are a combination and are relatively rare.

Origin of MeteoritesOrigin of Meteorites

• S- and M-type asteroids differentiated (yielding stony achondritic and iron meteorites).

• C-type did not (yielding stony chondritic).

Orbits of AsteroidsOrbits of Asteroids

• Most are in the asteroid belt between Mars and Jupiter.

• Near-Earth asteroids have orbits that cross that of the Earth.

• Apollo and Aten asteroids have such orbits.

Orbits of AsteroidsOrbits of Asteroids

• Orbits are prograde, in the same direction as the planets orbit.

• Circular or somewhat elongated.

• Orbits have small tilts from the plane of the Solar System.

AsteroidsAsteroids

• Asteroids are small, irregular bodies.• Most are composed of rock or metal.• It is possible for them to have moons.• Spacecraft have visited six of them.

CometsComets• Icy planetesimals found

beyond the planets.

• Located either in the Kuiper Belt or the Oort Cloud surrounding the Solar System.

CometsComets

• Nucleus is an ice/rock mix.

• “Dirty snowballs.”

• Size of nucleus ranges from a few dozen meters to a several hundred kilometers.

CometsComets

• When near the Sun, comets are “active.”

• Sun heats the icy nucleus, forming:– Coma (head)– Ion tail– Dust tail

Comet TailsComet Tails• Ion tail created by

the solar wind interacting with ions of the nucleus.

• Dust tail created from solar wind and sunlight.

• Comet tails point away from the Sun.

Orbits of Comets: Short-periodOrbits of Comets: Short-period

• Short-period comets: – Periods < few

centuries.– Near ecliptic plane.– Prograde orbits,

circular or somewhat elongated.

– Kuiper Belt.

Orbits of Comets: Long-periodOrbits of Comets: Long-period

• Long-period comets:– Periods of 1,000 to

maybe 1 million years.– Prograde or retrograde

orbits, from Oort Cloud.– Large tilts from the

ecliptic, very elongated orbits.

– Nucleus not “worn out.”

CollisionsCollisions• Large collisions are not frequent, but they occur.• 1994: Comet Shoemaker-Levy 9 crashed into

Jupiter, leaving visible scars.

Collisions with EarthCollisions with Earth

• Comet or asteroid impacts are infrequent, but devastating.

• 1908: Tunguska event was possibly the high-altitude explosion of an asteroid or comet.

Solar System DebrisSolar System Debris• Comet nucleus

disintegration and asteroid collisions make debris.

• Passing through cometary debris results in meteor showers.

• Atmospheric phenomena.

Solar System DebrisSolar System Debris• Sunlight reflects off

ground-up asteroid and cometary debris in the inner Solar System.

• This zodiacal dust in the plane of the Solar System makes the zodiacal light.

Concept Quiz Concept Quiz Asteroids Asteroids

Asteroids are made of

A. dust and gas.

B. ices and dust.

C. rock and metal.

D. frozen carbon dioxide (“dry” ice).

Concept Quiz – Distant CometsConcept Quiz – Distant Comets

A distant comet at its farthest point from the Sun would have

which of the following?

A. Dust tail

B. Ion tail

C. Nucleus

D. Coma

Concept Quiz – Short-period Concept Quiz – Short-period CometsComets

Short-period comets are associated with what class of objects?

A. Kuiper Belt objects

B. Terrestrial planets

C. The Oort Cloud

D. The giant planets

Comentary OrbitsComentary Orbits

Click the above picture to launch the animation

This concludes the Lecture PowerPoint presentationThis concludes the Lecture PowerPoint presentationfor Chapter 12for Chapter 12

©2010 W.W. Norton & Company, Inc.

For more learning resources, please visit the StudySpace website for 21st Century Astronomy athttp://wwnorton.com/studyspace

21st CENTURY ASTRONOMY

THIRD EDITIONHester | Smith | Blumenthal | Kay | Voss