MercuryVenus

EarthMars

JupiterSaturn

UranusNeptune Pluto

MyVery

Energetic Mother

JustServed

UsNine

Pizzas

Your Parents’ Solar System

Facts Are Not Knowledge

• Memorization, not understanding• Factoids• Highlights differences• Little or no relevance• Little or no “big picture”

Sun

Rocky Planets

Asteroid Belt

Giant Planets

Kuiper Belt

Oort Cloud

The 21st Century Solar System

Families of the Solar System

• Classes of similar objects– Size– Composition– Orbit size– Orbit shape– Orbit inclination– Moons– Rings

Hollywood’s View of the Asteroid Belt

Scientific View of the Asteroid Belt

960 million miles

Hundreds of thousands of asteroids …

… about a million miles apart!

Sizes of the Giant Planets and Earth

Kuiper Belt

Oort Cloud

• Billions of icy minor planets – comet nuclei

• Roughly spherical out to 50,000 AU

• Predicted by Jan Oort• Explains long-period

comets

Figure 1a: Comet Semimajor Axis Distribution

0

100

200

300

400

500

600

-0.0

04

-0.0

02

0.00

0

0.00

2

0.00

4

0.00

9

0.02

0

0.04

2

0.08

8

0.18

5

0.39

0

1 / a (1/AU)

Nu

mb

er o

f C

omet

s

Short PeriodLong Period

Orbital Period: 200 years 7 years

Sedna

Sedna

• Orbit 76 – 840 AU• Very red color

• Outer Kuiper Belt?• Inner Oort Cloud?• Planet at 70 AU?

Families of the Solar System

• Classification• Structure of the solar system

– Similar objects lie in similar regions• Clues to solar system formation and evolution

Rocky Planets Giant Planets

Sun

Rocky Planets

Asteroid Belt

Giant Planets

Kuiper Belt

Oort Cloud

Sun

Oort Cloud

Mercury Venus Earth Mars

Asteroid Belt Jupiter Saturn Uranus Neptune

Kuiper Belt

Science

Out Changes

May View Established Models

As Basic

Justified Standards Until New

Knowledge Bears

Sometimes

Over Coals

My Very Energetic Mother

Also Boils

Jumbo Shrimp Using Nine

Kettles Bubbling

The Inevitable Question …

Why is Pluto No Longer a Planet?

Planet Pluto

January 23, 1930

January 29, 1930

The Incredible Shrinking Planet

• Lowell’s Planet X – 7 times Earth• 1940’s – 1 times Earth• 1980 – 0.1 times Earth• 1985 – 0.002 times Earth

Double Take: Charon

• 1978 – James Christy (USNO) observations to refine Pluto’s orbit

• Notices elongated images, deduces moon• 1985 – Charon occults Pluto, confirms

existence• Refined sizes and masses – tiny

Pluto/Charon

Pluto

Triton

Titan

Callisto

Ganymede

Moon

Io

Europa

Mercury

Rhea

Iapetus

Titania

Oberon

Pallas

Vesta

Hygeia

Mimas

Enceladus

MirandaProteus

Ceres

Tethys Dione

Ariel Umbriel

Charon

Kuiper Belt

• 1930 – Leonard mentions possibility of trans-Plutonian objects

• 1943 – Kenneth Edgeworth postulates objects beyond Pluto

• 1951 – Gerard Kuiper predicts that a massive Pluto would disperse small objects into a belt

• 1980 – Fernandez predicts ‘comet belt’ that resembles what was eventually found

Kuiper Belt Objects

• 1992 – Jewitt & Luu find QB1

• Distance of 42 AU• First (third?) object

discovered in the Kuiper Belt

Kuiper Belt

More and more KBOs

• Large searches for KBOs ensued• Hundreds discovered within a decade• Over 1200 discovered so far• Over 70,000 predicted

– diameters > 100 km– orbits 30-50 AU

Pluto Defenders

• Pluto is different from the KBOs• Pluto is bigger than the KBOs• Pluto has a moon, Charon

Pluto/Charon orbits within Kuiper Belt

KBO Size ComparisonKBO Size Comparison

Binary KBOs

• About 10% of KBOs are binaries

Eris & Dysnomia (2003 UB313)

Eris & DysnomiaSanta & Rudolph

Easterbunny

Pluto vs the Kuiper Belt

• Orbit similar to KBOs• Size similar to KBOs• KBO companions common• Composition similar to KBOs

Pluto vs the Kuiper Belt

• Orbit similar to KBOs• Size similar to KBOs• KBO companions common• Composition similar to KBOs

Pluto has found its family!!

IAU Definition – August 2006• IAU defines “planet”

1. Orbits the Sun2. Upper mass limit

• not massive enough to produce fusion• Deuterium fusion occurs at about 15x Jupiter’s mass

3. Lower mass limit• Massive enough for gravity to make it spherical• About 500 miles in diameter

4. Dominates its orbit• Dwarf planets meet 1, 2, 3, but not 4

Other Planetary Systems?

• Solar system alone is category of one

Beta Pictoris

We Are Not Alone

• Lots of dust disks found• Proplyds – proto-planetary disks• Kuiper Belt sized and larger• Some substructure seen

Planets around Other Stars

• Cannot see directly (yet)• Detect via gravitational pull on star

– Wobble– Periodic shift of spectral lines– Monitor for many years (several orbits)– Giant planets detectable

Planets around Other Stars

• Current count (May 2006)– 162 planetary systems– 188 planets– 19 multiple planet systems

• At least 15% of sun-like stars have planets