Download Pluto is (still) not a planet

Pluto is (still) not a planet.
Prof. Richard Pogge
OSU Department of Astronomy
Science Café – 2013 Sept 11
Fool: The reason the seven stars are seven is a
pretty reason...
Lear: Because they are not eight?
Fool: Aye, indeed, thou wouldst make a good
fool.
William Shakespeare
King Lear (1605)
The Solar System in 1766
Saturn
Jupiter
Mars
Earth
Venus
Mercury
In 1766, Johann Titius noted that planet distances follow a
simple geometric progression with a gap between Mars &
Jupiter.
m=0
m
V
𝑎 = 0.4 + 0.3×2𝑚
1
2
E
M
3
4
5
J
S
Johann Bode published what we now
call the Titius-Bode Law in 1772.
Johann Daniel Titius
(1729-1796)
Johann Elert Bode
(1747-1826)
William Herschel discovered the
planet Uranus on 1781 March 13.
NASA
First new planet since antiquity,
but it is not a naked-eye planet.
Uranus fits the Titius-Bode law!
m
V
E
M
J
Where was the missing planet between
Mars & Jupiter?
S
U
In 1799, Baron Franz Xaver von Zach organized 24
astronomers into the “Celestial Police”.
Their charge:
To make a systematic
search for the "missing"
5th planet between Mars
and Jupiter predicted by
the Titus-Bode Law.
Baron Franz Xaver von Zach
(1754-1832)
Giuseppe Piazzi discovered
Ceres on Jan 1, 1801 while
looking for the "missing" star
Mayer 87.
Hubble Space Telescope
Giuseppe Piazzi (1746-1826)
Ceres was right where the Titius-Bode
Law said it should be.
m
V
E
M
c
J
But, things soon got complicated...
S
U
Heinrich Olbers discovered
Pallas on May 28, 1802 while
observing Ceres.
Hubble Space Telescope
Heinrich Wilhelm Matthäus Olbers
(1758-1840)
New problem: Pallas’ and
Ceres’ orbits crossed!
In 1802, William Herschel coins the term "asteroid"
("star-like"), rejecting the idea these are new planets.
They are very much smaller
than the other planets.
Their orbits are more tilted
and elliptical than the other
planets.
Ceres & Pallas cross each
other’s orbits.
Bristol City Museum & Gallery
By 1807, 4 new "planets" had been discovered in the
space between Mars & Jupiter
Vesta: 1807 (Olbers)
Ceres: 1801 (Piazzi)
Juno: 1807
(Harding)
Then nothing for 38 years...
Vesta (NASA/Dawn)
Pallas: 1802 (Olbers)
The discovery of Neptune in 1846 was a factor in
reclassifying Ceres, Pallas, Juno, and Vesta as
"Minor Planets“.
Urban Leverrier
Johann Galle
Predicted mathematically by Leverrier and Adams from the
orbital wobble of Uranus.
Found by Galle at Leverrier’s predicted position.
Violates the Titius-Bode law by 30% (closer than “predicted”).
Wealthy amateur Percival Lowell began a search for
a planet beyond Neptune in 1909.
It was expected from residual
wobbles in Uranus’ and
Neptune’s orbits.
Built a private observatory in
Flagstaff, AZ.
Actually photographed Pluto
twice but didn't notice it.
Percival Lowell (1855-1916)
Pluto was discovered
photographically by
Clyde Tombaugh on
February 18, 1930.
Clyde Tombaugh at the Lowell
Blink Comparator
Lowell "Pluto" Astrograph
The new planet was named Pluto, and became
immediately controversial.
It is too small to cause
orbit wobbles in Uranus or
Neptune.
Its orbit is highly tilted and
elliptical.
Its orbit crosses the orbit of
Neptune.
But, nobody questioned that it was a planet...
Pluto
Neptune
Pluto is a tiny, cold, icy world orbiting far from
the Sun.
Temperatures: −378 to −396º F
Rocky core over an icy mantle.
Surface is covered with frozen
gases.
Has a thin nitrogen atmosphere.
Pluto has 1 large moon (Charon) and 4 smaller moons.
Hubble Space Telescope
Pluto is smaller than our Moon.
Pluto and its large moon Charon have the largest
parent-to-moon mass ratio in the Solar System.
In the 1950s, Edgeworth and Kuiper predicted the
existence of a large population of small icy bodies
beyond the orbit of Neptune.
The first discovered in 1992
by Jewitt & Luu.
Hundreds more were found
by the early 2000s.
All are smaller than Pluto,
but many have similar orbital
characteristics.
We now call this the “Kuiper Belt”
JHU/APL
Flattened belt of icy objects between 30 and 50 AU
from the Sun (from Neptune’s orbit to beyond Pluto).
In January 2005, Brown, Trujillo, and Rabinowitz
discover 2003UB313 and set off a controversy.
It is about the same size as Pluto.
It has a very elliptical & tilted orbit
It has a Pluto-like composition.
It has 1 moon, resulting in a mass
a little larger than Pluto’s.
Was it the 10th planet?
Mike Brown
Chad Trujillo David Rabinowitz
The group's codename for the new object was "Xena"
The official name chosen was “Eris”
The goddess of discord…
In August 2006, the IAU took up the question of
how to define a “planet”.
1. Orbits around the Sun and is not a satellite.
2. Shaped by Gravity: sufficient mass to assume a
spheroidal shape.
3. Has cleared its orbital neighborhood
("orbital dominance")
Three Dwarf Planets: Ceres, Pluto, & Eris
The Solar System in September 2013
Gas Giants
Terrestrials
Ice Giants
Dwarf Planets
The Terrestrial Planets are the rocky planets found
in the inner Solar System 0.4–1.5 AU from the Sun.
Mercury
(0.055 ME)
Venus
(0.82 ME)
Mars
(0.11 ME)
Earth
(1 ME)
Composed of mostly Silicates and Iron with solid surfaces
All are High Density: 3.9 – 5.5 g/cc (rock & metal)
Jupiter & Saturn are Gas Giants with thick Hydrogen
& Helium atmospheres over rock & ice cores
Saturn:
95.2 ME
9.44 RE
Jupiter:
318 ME
11.2 RE
Uranus and Neptune are Ice Giants made mostly of
ices with thin Hydrogen & Helium atmospheres.
Uranus
Neptune
14.5 ME
4.01 RE
17.1 ME
3.88 RE
The Dwarf Planets
Pluto
Makemake
Eris
Ceres
Haumea
40+ other candidates…
Moon
Earth
The most controversial and least well-defined
criterion is “orbital dominance”.
The "One planet per orbit" rule.
Examples:
1. Anything near Earth has its orbital altered by
the gravitational influence of Earth.
2. Ceres and Pallas have orbits that cross, so
neither "dominates" its orbit.
3. Pluto is in a 3:2 resonance with Neptune,
and its motion is dominated by Neptune.
Planet
Clears its orbit quickly compared to age of the Solar System
Dwarf
Not enough time to have cleared its orbit
Pluto and Eris are the largest of a new family of
Trans-Neptunian Objects.
More than 1000 known today.
Could be as many as ~70,000
more than 100 km in diameter.
The largest are >1000 km in diameter.
Total combined mass could be
2% to 4% the mass of Earth.
Icy material leftover from the
formation of the Solar System
The New Horizons mission was launched in 2006 to
study Pluto and the Kuiper Belt up close.
Launch: January 19, 2006
Pluto fly-by: July 14, 2015
Explore Kuiper Belt 2016-2020
Pluto & Charon, July 2013
New Horizons at Pluto
Further Reading:
The Pluto Files
Neil deGrasse Tyson
How I Killed Pluto
and Why it Had it Coming
Mike Brown
(see pages 165-175)