What Happened to Pluto?!!
Scale in the Solar System, New Discoveries, and the Nature of Science
Mary L. Urquhart, Ph.D.
Department of Science/Mathematics Education
Marc Hairston, Ph.D.
William B. Hanson Center for Space Sciences
From Nine to Eight?
On August 24th Pluto was reclassified by the
International Astronomical Union (IAU) as a
“dwarf planet”.
So what happens to “My Very Educated Mother
Just Served Us Nine Pizzas”?
Official IAU Definition
A planet:
(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 neighborhood around its orbit.
A dwarf planet must satisfy only the first two criteria.
What is Science?
National Science Education Standards
(National Research Council, 1996)
“…science
reflects its history and is an ongoing,
changing enterprise.”
Beyond Mnemonics
Science is “ not a collection of facts but an
ongoing process, with continual revisions and
refinements of concepts necessary in order to
arrive at the best current views of the Universe.”
- American Astronomical Society
A Bit of History
• How have planets been historically defined?
• Has a planet ever been demoted before?
Planet (from Greek “planetes” meaning wanderer)
This was the first definition of “planet”
planet
Sun
Moon
Mars
Mercury
Jupiter
Venus
Saturn
Latin
Solis
Lunae
Martis
Mercurii
Jovis
Veneris
Saturni
English
Spanish
Sunday
domingo
Monday
lunes
Tuesday
martes
Wednesday miércoles
Thursday
jueves
Friday
viernes
Saturday
sábado
Italian
domenica
lunedì
martedì
mercoledì
giovedì
venerdì
sabato
French
dimanche
lundi
marti
mercredi
jeudi
vendredi
samedi
Copernican Revolution
(16th Century)
“Planet” now means “any celestial body orbiting the Sun.”
The second time we’ve defined the word “planet.”
Ptolemy
Copernicus
Find these images and learn more about the Universe models of Ptolemy and Copernicus at
http://www.pbs.org/wnet/hawking/universes/html/univ_coper.html
In 1801, 20 years
after the discovery
of Uranus, Ceres
was discovered by
Giuseppe Piazzi.
Cerese was
demoted to asteroid
after the discovery
of many other
objects in similar
orbits.
“Planet” became defined as “any celestial body orbiting the
Sun that is ‘big enough,’ in other words Mercury-sized or
bigger.” The third time we’ve defined the word “planet.”
The hunt for
Planet X
(1903-1916)
Clyde Tombaugh 1904 - 1997
Problems with
Pluto’s mass
(this is the only scary
mathematical plot
that we’ll use here,
we promise!)
from Dessler and Russell (1980)
Discovery of Charon
in 1978
Images courtesy of the U.S. Navel Observatory and
NASA/HST/ESA
Pluto and Charon
Pluto and Charon as imaged by the Hubble Space Telescope in 1994
Image Credit: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA
The
Kuiper
Belt
Image from
http://www.ap.stmarys.ca/~ishort/Images/SolSystem/
1992 QB1
The first Kuiper Belt Object (KBO) was discovered in 1992
Diameter: 200 km
A 1992 discovery image of 1992 QB1 (indicated by the arrow) captured by Jewitt and Luu using the University of Hawaii's
2.2 m telescope on Mauna Kea, from http://science.nasa.gov/headlines/y2001/ast13sep_1.htm
More Kuiper Belt Objects (KBOs)
More than 1000 KBOs
have now been found.
100,000 may be
detectable from Earth.
1000 km
Image Credit: NASA JPL-Calech
Neptune’s Moon Triton:
A Captured KBO
Image credit: Paul M. Schenk, Lunar and Planetary Institute
Is Pluto Just a KBO?
UB313: Bigger than Pluto!
An NASA artist’s conception (left) and an actual Hubble Space
Telescope image (right) of a 2400 km diameter Kuiper Belt Object
orginally called UB313, discovered by Michael Brown.
Credit: NASA, ESA, and M. Brown (California Institute of Technology)
So, What is a Planet?
Dysnomia
Eris
Image Credit: NASA, ESA, and A. Feild
(STScI)
Scale in the Solar System
We’ll use a scale model of the solar system using a 1:10 billion
scale factor, and including 8 planets and the first 3 dwarf
planets:
1. Ceres
2. Pluto
3. Eris
Size?
“... anything bigger than
TEXAS is certainly not
minor, not small, and not a
dwarf,
Therefore, a planet must
be any star-orbiting, nonfusing celestial body larger
than the smallest sphere
containing TEXAS.”
-Bob Johnson
Graduate Student
UT Dallas
http://www.johnstonsarchive.net/astro/planettexas.htm
Smaller than Many Moons
Ida and Dactyl
10 km
Roundness Criteria
Should everything round
be a planet?
Saturn’s moon, Mimas
Diameter: 394 km
Demoted Ceres is Round!
Diameter = 930 km
12 Planets?
Distance Not to Scale!
Image Credit: IAU
One
(or two)
in a growing
family
Image Credit: NASA, ESA, and A. Feild (STScI)
Leftovers of Planetary Formation
Image Credit: Lunar and Planetary Institute
Not Everyone is Happy!
Image Credit: Associated Press
Pluto is Still Pluto!
The solar system hasn’t changed - only our understanding
of it (and our nomenclature) has…
New Horizons - On Its Way!
NASA’s New Horizon’s Spacecraft will reach Pluto in July 2015,
and continue on to encounters with other Kuiper Belt Objects.
Learn more at: http://pluto.jhuapl.edu/
UB313 has its place…
Meet Eris: the largest
known dwarf planet
Only Eight Planets
My Very Educated Mother Just Served Us Nachos.
Instead of:
My Very Esteemed Mentor Certainly Just Surprised
Us, Now Pondering Curie's X-ray…
My very educated mother carefully just showed us
nine charred pizza xeroxes…
In Summary
• The term “planet” has been redefined at least
three times.
• Pluto is much smaller (and less massive) than
originally thought.
• Pluto is a large, but not the largest, KBO
• Pluto is still important to scientists, and will be
visited by New Horizons in July 2015.
The Nature of Science
The Nature of Science
• Science is dynamic - new data leads to new
understanding.
• Science is a human endeavor - human beings
make - and interpret - discoveries.
Classroom Strategies
• Discuss the current controversy about Pluto.
• Create classifications for solar system objects.
• Discuss the history of solar system exploration.
• Research unanswered questions.