Transcript Document 7220706

The Pluto Controversy
http://apod.nasa.gov/apod/astropix.html
What is a Planet????
The problem is that astronomers have
never defined what a planet is.
Some History
• In ancient times there were seven planets
– Moon
– Mercury
– Venus
– Sun
– Mars
– Jupiter
– Saturn
Some History
• After Copernican revolution there were 6
planets
– Mercury
– Venus
– Earth
– Mars
– Jupiter
– Saturn
Some History
Asteroids 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?
Some History
• By 1890 over 300 objects had been found
orbiting between Mars and Jupiter and
were being called minor planets or
asteroids.
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.
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
Pluto’s 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!!!!
Pluto is Strange
• Orbit of Pluto comes
inside orbit of
Neptune.
• Is Pluto an escaped
moon of Neptune?
Maybe and maybe
not.
Pluto is Strange
• Pluto’s 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/16_plutoOrbit.html
Pluto is Strange
• After discovery of
Charon the mass of
Pluto was determined
to be 0.0021 times
the Earth’s mass.
Pluto is Strange
http://solarviews.com/eng/pluto.htm
Pluto and Charon are about the size of the USA.
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
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
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.
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.
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 Earth’s density.
• Pluto’s size is closer to being an asteroid
than a planet.
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.
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.
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.
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.
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.