The Pluto Controversy

1
The Pluto Controversy
http//apod.nasa.gov/apod/astropix.html
2
What is a Planet????

• The problem is that astronomers have never
  defined what a planet is.

3
Some History

• In ancient times there were seven planets
• Moon
• Mercury
• Venus
• Sun
• Mars
• Jupiter
• Saturn

4
Some History

• After Copernican revolution there were 6 planets
• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn

5
Some HistoryAsteroids were originally classed as
planets.

• Uranus discovered in 1781
• Ceres (asteroid)) discovered in 1801. It was
  assumed to be the missing planet between mars and
  Jupiter!
• Pallas 1802 (asteroid)
• Juno 1804 (asteroid)
• Vesta 1807 (asteroid)
• Neptune discovered in 1846
• Now are there 12 planets?

6
Some History

• By 1890 over 300 objects had been found orbiting
  between Mars and Jupiter and were being called
  minor planets or asteroids.

7
Some History

• More planets were being discovered between Mars
  and Jupiter
• New classification as asteroids
• Ceres
• Juno
• Vesta
• et al.
• Now we have reduced the number of planets from 12
  to 8.
• Therefore, in the past astronomers have
  reclassified objects from being planets to being
  something else.

8
Discovery of Pluto

• March 13, 1930 by Clyde Tombaugh at Lowell
  Observatory (Percival Lowell).
• 6 degrees from predicted location
• Inclined 17 degrees from plane of Solar System
• Assumed to be like the Earth

9
Plutos Moon

• Charon discovered at USNO Flagstaff, AZ in July
  1978.
• Pluto's mass 0.0021 Earth masses.
• NOT SO EARTH LIKE!!!!!!
• My teachers lied to me!!!!

10
Pluto is Strange

• Orbit of Pluto comes inside orbit of Neptune.
• Is Pluto an escaped moon of Neptune? Maybe and
  maybe not.

11
Pluto is Strange

• Plutos obit is the most highly inclined orbit of
  all the planets.
• i 17 degrees
• Therefore, Neptune and Pluto can not collide.

http//pluto.jhuapl.edu/science/everything_pluto/1
6_plutoOrbit.html
12
Pluto is Strange

• After discovery of Charon the mass of Pluto was
  determined to be 0.0021 times the Earths mass.

13
Pluto is Strange
http//solarviews.com/eng/pluto.htm

• Pluto and Charon are about the size of the USA.

14
The Ort Cloud and Kuiper Belt

• In 1950, Dutch astronomer Jan Oort hypothesized
  that comets came from a vast shell of icy bodies
  about 50,000 times farther from the Sun than
  Earth is. A year later astronomer Gerard Kuiper
  suggested that some comet-like debris from the
  formation of the solar system should also be just
  beyond Neptune.

http//www.solarviews.com/eng/kuiper.htm
15
Kuiper Belt

• The Kuiper belt remained theory until the 1992
  detection of a 150-mile wide body, called 1992QB1
  at the distance of the suspected belt. Several
  similar-sized objects were discovered quickly
  confirming the Kuiper belt was real.

http//www.solarviews.com/eng/kuiper.htm
16
WW31

• This illustration compares the orbit of the
  binary Kuiper Belt object, called 1998 WW31, with
  the orbits of Pluto and Neptune, the outermost
  solar system planets. The inset picture,
  consisting of six snapshots taken by NASA's
  Hubble Space Telescope, shows one member of the
  Kuiper Belt pair the faint white blobs during
  its elliptical orbit. The bright white object at
  the bottom of the oval is the other member of the
  pair.

17
Quaoar, an Icy World Far Beyond Pluto

• Quaoar, an Icy World Far Beyond Pluto With the
  help of NASA's Hubble Space Telescope,
  astronomers have determined that 2002 LM60, an
  icy Kuiper belt object dubbed "Quaoar," by its
  discoverers, is the largest body found in the
  solar system since the discovery of Pluto 72
  years ago. Quaoar (pronounced kwa-whar) is about
  half the size of Pluto. Like Pluto, Quaoar dwells
  in the Kuiper belt.

18
Some Reasons Pluto may not be a Planet

• Orbital inclination out of plane of Solar System
• Other similar object found nearby that are
  considered Kuiper Belt objects.
• Mass is very low (0.002) and more like that of a
  asteroid or comet than a planet.
• Density is 0.373 times the Earths density.
• Plutos size is closer to being an asteroid than
  a planet.

19
Explanation How many planets are in the Solar
System? This popular question now has a new
formal answer according the International
Astronomical Union (IAU) eight. Last week, the
IAU voted on a new definition for planet and
Pluto did not make the cut. Rather, Pluto was
re-classified as a dwarf planet and is considered
as a prototype for a new category of
trans-Neptunian objects. The eight planets now
recognized by the IAU are Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, and Neptune. Solar
System objects now classified as dwarf planets
are Ceres, Pluto, and the currently unnamed 2003
UB313. Planets, by the new IAU definition, must
be in orbit around the sun, be nearly spherical,
and must have cleared the neighborhood around
their orbits. The demotion of Pluto to dwarf
planet status is a source of continuing dissent
and controversy in the astronomical community.
20
What is a planet?

• The IAU members gathered at the 2006 General
  Assembly agreed that a "planet" is defined as a
  celestial body that (a) is in orbit around the
  Sun, (b) has sufficient mass for its self-gravity
  to overcome rigid body forces so that it assumes
  a hydrostatic equilibrium (nearly round) shape,
  and (c) has cleared the neighbourhood around its
  orbit.

21
What is Pluto?

• A new distinct class of objects called "dwarf
  planets" was also decided. It was agreed that
  "planets" and "dwarf planets" are two distinct
  classes of objects. The first members of the
  "dwarf planet" category are Ceres, Pluto and 2003
  UB313 (temporary name). More "dwarf planets" are
  expected to be announced by the IAU in the coming
  months and years. Currently a dozen candidate
  "dwarf planets" are listed on IAU's "dwarf
  planet" watch list, which keeps changing as new
  objects are found and the physics of the existing
  candidates becomes better known.
• The "dwarf planet" Pluto is recognized as an
  important proto-type of a new class of
  trans-Neptunian objects. The IAU will set up a
  process to name these objects.

22
The Redefined Solar System

• Pluto demoted to a dwarf planet.
• Ceres promoted to dwarf planet and NOT an
  asteroid.
• I guess we are making this stuff up as we go.

23
Nature of Science

• Science is tentative.
• Science is created by humans using logical
  reasoning and creativity.
• Scientific knowledge is our best logical guess
  and may change as needed.