Confessions of a Pluto HaterConfessions of a Pluto Hater

Megan K. PickettMegan K. PickettAssociate Professor of PhysicsAssociate Professor of PhysicsLawrence UniversityLawrence University

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14 November 200614 November 2006

Friends, Students, Scientists, lend me your ears;I come to bury Pluto, not to praise it.The evil this rock does lives in our books, The small good was interred with Clyde's bones;So let it be with Pluto...The noble NewtonHath told you Pluto was Perturber:If it were so, it was a grievous fault,And grievously hath Pluto not answer'd it...Here, under leave of Lowell and the rest-(For Lowell was a crazy nearsighted man;who saw lines on Mars and shouted "water, ho!")-Come I to speak on Pluto, Dwarf Planet...

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

Formerly the Ninth Planet of the Solar SystemFormerly the Ninth Planet of the Solar System

uto

Average Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

The Pluto Formerly Known as PlanetThe Pluto Formerly Known as PlanetAverage Orbital Distance: 40 AU

Orbital Period: 248 years

Orbital Inclination: 17o

Orbital Eccentricity: 25%

Rotation Period: -6.4days

Radius: 0.6 RM

Mass: 0.3MM

Average Density: 2100 kgm-3

Surface Temperature: 33 - 55 K

Atmosphere: CH4 and N2

Surface: CH4 ice (?)

Interior (?): Silicates &

ices

History of DiscoveryHistory of DiscoveryClassical Planets: Mercury, Venus, Mars, Jupiter & Saturn

Uranus: (1781) Herschel

Neptune: (1864) Adams & Leverrier

Ceres: (1801) Piazzi

(asteroid and now

Dwarf Planet)

History of DiscoveryHistory of Discovery

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are needed to see this picture. Percival Lowell

Clyde Tombaugh

Pluto: 1930

I.A.U. Circulaire No. 255

BUREAU CENTRAL ASTRONOMIQUEDE L'UNION ASTRONOMIQUE INTERNATIONALEOBSERVATOIRE DE COPENHAGUE

TRANSNEPTUNIAN PLANET?

Lowell observatory telegraphs systematic search begun years ago supplementing Lowells investigations for Transneptunian planet has revealed object which for seven weeks has in rate of motion and path consistently conformed to transneptunian body at approximate distance he assigned fifteenth magnitude position march twelve three hours G.M.T. was seven seconds of time west from delta geminorum agreeing with Lowells predicted longitude.

History of DiscoveryHistory of Discovery

Nix & Hydra: (2005)Pluto Companion Search Team

Charon: (1978) Christy

History of DiscoveryHistory of Discovery

1990’s: Here come the Kuiper Belt Objects!

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1992: 1992 QB1

David Jewitt &Jane Luu.

Currently ~1000 KBO’sknown.

History of DiscoveryHistory of Discovery

Late 1990’s to Present: A TransNeptunian Zoo.

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History of DiscoveryHistory of Discovery

And then there was Eris (& Dysnomia): “Scatter Disk Object”

2005 Brown, Trujillo & Rabinowitz

A Brief History of the Solar SystemA Brief History of the Solar System

1. Collapse of cold pre-stellar cloud (~5GYA)a) Initial cloud contains mass and angular momentum of

Solar systemb) Why does it collapse?

• Marginally unstable to collapse?• Triggered collapse?

100 AU0.1 pc 105 yrs

A Brief History of the Solar SystemA Brief History of the Solar System

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Well, what next?

A Brief History of the Solar SystemA Brief History of the Solar System

2. The Solar Nebula (Kant 1775, Laplace 1796)

a) Close to the Protosun(inside the “frostline”), volatiles are vaporized, andonly refractory elements areavailable for planet buildingby accumulation and then accretion.

~8 AU

Inner planets are rocky

A Brief History of the Solar SystemA Brief History of the Solar System

2. The Solar Nebula (Kant 1775, Laplace 1796)

b) Far from the Proto-Sun, Ices are also available forBuilding planetary cores.

~80 AU

Outer Solar System is(or should be) very differentfrom inner Solar System.

A Brief History of the Solar SystemA Brief History of the Solar System

3. Planet Formation

a) Terrestrial Planets: relatively straightforward.b) Gas & Ice Giant Planets: Phasers at Dawn.

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“Core Accretion”

Takes Too Long

“Spiral Instability”

Doesn’t Work

vs.

A Brief History of the Solar SystemA Brief History of the Solar System

4. Planet Billiardsa) Jupiter, Saturn, Uranus & Neptune migrate after

formation (e.g., the “Nice Model” 2004)

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•Initially J,S close; Neptune inside Uranus orbit; KBO 20-30 AU•J,S migrate in and out, respectively=> fling out Neptune, KBO’s•Neptune clears primordial KB, captures Triton, perturbs PLUTO

A Brief History of the Solar SystemA Brief History of the Solar System

4. Planet Billiardsb) Bombardment

•Forms Earth & Moon•May form Martian satellites•May form Pluto-Charon

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A Brief History of the Solar SystemA Brief History of the Solar System

4. Planet Billiardsc) Populate Scattered Disk, Oort Cloud.d) Delivers volatiles to inner solar system.

5. Solar Ignitiona) Hydrogen Fusion (p-p chain) begins in core of Sun

So where does this leave Poor Old Misbegotten Pluto?So where does this leave Poor Old Misbegotten Pluto?

Pluto is Not a PlanetPluto is Not a Planet

1. On August 24 2006, members of the IAU finally came to their collected senses and voted Pluto out of the Ritzy Planet Club. Was this mean? Logical? Or both?

What’s the caseagainst Pluto?

Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

a) Pluto is Bloody Tiny.a) Pluto is Bloody Tiny.

Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

b) Pluto’s orbit is unlike any of the other planets.b) Pluto’s orbit is unlike any of the other planets.

Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

c) There are a lot of tiny icy bodies out there, too.c) There are a lot of tiny icy bodies out there, too.

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Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

d) Pluto is a binary objectd) Pluto is a binary object

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What to do about Pluto, then?What to do about Pluto, then?

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Fortunately, we already have an object parked in SaturnOrbit that seems right for the job.

Real Planets don’t look like tiny plates of quicheReal Planets don’t look like tiny plates of quiche

2.2. Thus Sayeth the IAU:Thus Sayeth the IAU:

A Planet is an object that 1. orbits the Sun (so far so good);A Planet is an object that 1. orbits the Sun (so far so good);2. is massive enough to pull itself into a sphere (again, 2. is massive enough to pull itself into a sphere (again, good enough); and 3. has cleared the region of objects, i.e.,good enough); and 3. has cleared the region of objects, i.e.,is in some sense locally gravitationally independent. is in some sense locally gravitationally independent.

And so, mercifully, Pluto, along with Eris andAnd so, mercifully, Pluto, along with Eris andCeres and probably many, many more areCeres and probably many, many more are‘‘Dwarf Planets’.Dwarf Planets’.

D’Oh!

“Now cracks an icy sheath. Good night, odd ball,And flights of comets sing thee to Kuiper!"

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