Transcript Honey, I Shrunk the Solar System

Honey, I Shrunk the Solar
System
or
Pluto We Barely Knew Ye as a Planet
Image credit JPL
The Way it Was…
Image from JPL
And Then There Were Eight
Image from JPL
From Where Did the Word Planet
Come?
• The word “planet” is derived from the Greek
word for “wanderer” and was traditionally applied
to any heavenly body that moved with respect to
the stars. In this sense the Sun and Moon were
also planets.
• Dictionary says that a planet is any one of the
nine large bodies that orbit the Sun.
• But some objects have been found that are
larger than Pluto- so are they planets?
Who Discovered the First Planets?
• Ancient cultures knew that some objects
were not fixed in the sky like the stars.
• The Greeks knew of five such objects:
Mercury, Venus, Mars, Jupiter and Saturn
• By 800 B.C.E. Babylonian astronomers
had records of planetary motion for Venus,
Jupiter and Mars.
The Solar System Until 1781:
Mercury, Venus, Earth, Mars, Jupiter and Saturn
Images from NASA
The Solar System Grows: What to
Name a New Planet?
• March 13, 1781 William
Herschel discovers what he
thinks is a comet, but he has
discovered a new planet- the
seventh in our Solar System.
• Herschel wanted to name the
new planet George after King
George III of England.
• It was decided to continue with
the Roman god names that
had been used for the other
planets, thus it was named
Uranus.
• This set the standard for the
convention of using Roman
god names for the planets.
Uranus- The First New Planet
• Distance: 19.1 AU
Doubled the size of
the Solar System
• Diameter: about 4
Earth diameters
Image courtesy of
NASA
Another New World: Neptune
• The orbit of Uranus was not as expected.
• John Couch Adams, a 24 year old Cambridge grad,
thought that this might be caused by another unknown
planet
• In 1845 he submitted his calculations to the Astronomer
Royal of England. English star charts not good enough.
• At nearly the same time French astronomer Urbain Jean
Joseph Le Verrier did the same calculations. The Berlin
Observatory was given his data and the planet was
found the first night due to better star maps.
Neptune
• Following the Roman
god theme the planet
was named Neptune,
for the sea god since
it was blue
• 30 AU from the Sun
• Diameter: about 4
Earth diameters
Image by Hubble Space
Telescope
A Ninth Planet?
• Speculations about a ninth planet date back to the late 1800’s.
• Percival Lowell urged that a special camera be built to look for
Planet X.
• In 1929 the camera was finished and installed at Lowell Observatory
in Flagstaff, AZ
• Clyde Tombaugh discovered Pluto on February 18, 1930 after
looking at over one million stars
• Name Pluto suggested by Venetia Burney, an 11 year old girl. Pluto
was the Roman god of the underworld.
Clyde Tombaugh 1906-1997
Left: Young Clyde Tombaugh at
Lowell Observatory after the
discovery of Pluto.
Above: Dr. Tombaugh contemplates
his discovery of Pluto during a 1988
visit to the Powell Observatory in
Louisburg, Kansas. Photo credit Vic
Winter
Finding Pluto
Pluto images by Nathan Twining Observatory
Here it is!
Pluto images by Nathan Twining
Observatory
Pluto
• 39.5 AU from Sun
• Diameter: about 0.18 Earth
diameter (about 1400 miles)
• Pluto and Charon essentially a
double system
• NASA New Horizons mission
will reach Pluto in 2015
Image by Hubble Space
Telescope
• Pluto has been assigned
asteroid number 134340 by the
Minor Planet Center
The Arguments for and Against
Planethood for Pluto
• It is round like a planet
and it orbits the Sun.
• Pluto very small
• Doesn’t fit into any other
categories of planetsterrestrial or gas giants
• Orbit strange- tilted 17°
from plane of the solar
system
• May be typical of
thousands of icy objects
found far from the Sun
Image by JPL
The Kuiper Belt
John Hopkins University
Orbital Paths of Planets and Pluto
Orbit of Eris
(Formerly known as 2003 UB 313 or Xena)
NASA
Kuiper Belt Object Sizes
The International Astronomical
Union Resolution
• A planet is for the first time defined scientifically. A planet
orbits a star, has sufficient gravity to become round, and
has cleared the neighborhood around its orbit.
• A Dwarf Planet orbits the Sun, is not a satellite, has
sufficient gravity to become round and has not cleared
the neighborhood of its orbit. Pluto is the prototype of
this class and currently includes Ceres and Eris. Others
will be decided upon later.
• A third class, Small Solar System Bodies, was defined as
all other objects except satellites. This includes most
asteroids, most comets and most trans Neptune objects.
So Long Planet Pluto and
Hello Plutoids!
International Astronomical Union
And yet another change….
June 11, 2008
News Release - IAU0804: Plutoid
chosen as name for Solar System
objects like Pluto
Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater
than that of Neptune that have sufficient mass so they have a near-spherical
shape, and that have not cleared the neighborhood around their orbit. Satellites of
plutoids are not plutoids. The two known and named plutoids are Pluto and Eris.
Ceres is the only dwarf planet.
The Public Responds
This humorous image was created for a special “Save Pluto” contest held on
www.worth1000.com in response to public outcry about the demotion of
Pluto. It does not represent a real eventuality, but is used here to show how
passionately people have responded to the change in Pluto’s status.