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1. Confessions of a Pluto Hater
Megan K. Pickett
Associate Professor of Physics
Lawrence University
14 November 2006

2. 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 Newton
Hath 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...

3. Formerly 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

4. Formerly 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

5. Formerly 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

6. Formerly 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

7. Formerly 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

8. Formerly 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

9. The Pluto Formerly Known as Planet
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

10. History of Discovery
Classical Planets: Mercury, Venus, Mars, Jupiter & Saturn
Uranus: (1781) Herschel
Neptune: (1864) Adams & Leverrier
Ceres: (1801) Piazzi
(asteroid and now
Dwarf Planet)

11. History of Discovery
Percival Lowell
Clyde Tombaugh
Pluto: 1930

12. I.A.U. Circulaire No. 255
BUREAU CENTRAL ASTRONOMIQUE
DE L'UNION ASTRONOMIQUE INTERNATIONALE
OBSERVATOIRE 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.

13. History of Discovery
Nix & Hydra: (2005)
Pluto Companion Search Team
Charon: (1978) Christy

14. History of Discovery
1990’s: Here come the Kuiper Belt Objects!
1992: 1992 QB1
David Jewitt &
Jane Luu.
Currently
~1000 KBO’s
known.

15. History of Discovery
Late 1990’s to Present: A TransNeptunian Zoo.

16. History of Discovery
And then there was Eris (& Dysnomia): “Scatter Disk Object”
2005 Brown, Trujillo &
Rabinowitz

17. A Brief History of the Solar System
1. Collapse of cold pre-stellar cloud (~5GYA)
a) Initial cloud contains mass and angular momentum of
Solar system
b) Why does it collapse?
• Marginally unstable to collapse?
• Triggered collapse?
100 AU
0.1 pc 105 yrs

18. A Brief History of the Solar System
Well, what next?

19. A 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, and
only refractory elements are
available for planet building
by accumulation and then
accretion.
~8 AU
 Inner planets are rocky

20. A Brief History of the Solar System
2. The Solar Nebula (Kant 1775, Laplace 1796)
b) Far from the Proto-Sun,
Ices are also available for
Building planetary cores.
~80 AU
 Outer Solar System is
(or should be) very different
from inner Solar System.

21. A Brief History of the Solar System
3. Planet Formation
a) Terrestrial Planets: relatively straightforward.
b) Gas & Ice Giant Planets: Phasers at Dawn.
“Core Accretion”
Takes Too Long
“Spiral Instability”
Doesn’t Work
vs.

22. A Brief History of the Solar System
4. Planet Billiards
a) Jupiter, Saturn, Uranus & Neptune migrate after
formation (e.g., the “Nice Model” 2004)
•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

23. A Brief History of the Solar System
4. Planet Billiards
b) Bombardment
•Forms Earth & Moon
•May form Martian satellites
•May form Pluto-Charon

24. A Brief History of the Solar System
4. Planet Billiards
c) Populate Scattered Disk, Oort Cloud.
d) Delivers volatiles to inner solar system.
5. Solar Ignition
a) Hydrogen Fusion (p-p chain) begins in core of Sun
So where does this leave Poor Old Misbegotten Pluto?

25. Pluto 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 case
against Pluto?

26. Real Planets don’t look like tiny plates of quiche

27. Real Planets don’t look like tiny plates of quiche
a) Pluto is Bloody Tiny.

28. Real Planets don’t look like tiny plates of quiche
b) Pluto’s orbit is unlike any of the other planets.

29. Real Planets don’t look like tiny plates of quiche
c) There are a lot of tiny icy bodies out there, too.

30. Real Planets don’t look like tiny plates of quiche
d) Pluto is a binary object
What to do about Pluto, then?

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

32. Real Planets don’t look like tiny plates of quiche
2. Thus Sayeth the IAU:
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,
good enough); and 3. has cleared the region of objects, i.e.,
is in some sense locally gravitationally independent.
And so, mercifully, Pluto, along with Eris and
Ceres and probably many, many more are
‘Dwarf Planets’.
D’Oh!

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