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How many planets are there in our Solar System?
Poll Question:
Taking an Inventory of the Solar System
PlutoNeptune Comet
UranusMarsEarth
Saturn
Mercury
Sun
Venus
Jupiter
http://www.cfa.harvard.edu/iau/lists/InnerPlot.html
Solar System Table of Contents:
I. SunII. Mercury, Venus, Earth, MarsIII. Asteroid BeltIV.Jupiter, Saturn, Uranus, NeptuneV. Kuiper Belt (icy asteroids)VI.Oort Cloud (comets)
SIZE SHAPE ORBIT TEMP COMP
Which of the following criteria are important for defining a planet?
Size and Shape: Earth is spherical, asteroid Gaspra is not.
12,800 kilometers(avout 8000 miles)
15 kilometers(about 9 miles)
Asteroid Ceres is spherical and about the size of Texas. Is it a planet?
Io Europa Ganymede Callisto
MoonMercury
MarsPluto
Definition so far:a) Orbits the Sun;b) Is at least as large as Pluto.
Ceres GanymedeYES NO YES NO
Orbital Characteristics
Mercury Earth Mars
7° Venus
SaturnJupiter
Uranus
Neptune
Pluto
17°
Poll Question:
Why is Pluto’s orbit different from those of the other 8 planets?
Discovery of Kuiper Belt Objects
• 1992, Jane Luu and David Jewitt
• More than 1,000 KBO’s now known
• 11 Pluto-sized KBO’s
• Pluto is a Kuiper Belt Object
How to Find Kuiper Belt Objects
The Orbits of Some Kuiper Belt Objects
Artist’s Depiction of UB313
Credit: Robert Hurt (IPAC)
UB313(1500 miles)
Should UB313 be the 10th Planet in the Solar System?
Yes No
Size Orbit History Population
Which of the following criteria are important for defining a planet?
193 planets orbiting other stars (a total of 155 systems) have been identified to date.
What do they tell us?
Most are in elliptical orbits
Gas giants are seen orbiting very close to their parent star!
Copyright © 1998-2006 Lynette R. Cook
Three planets all within 0.2 AU (Mercury orbits at 0.4 AU!)
Giant planets with 10x’s the mass of Jupiter.
Copyright © 1998-2006 Lynette R. Cook, All Rights Reserved
The International Astronomical Union is
working to craft a definition that satisfies both Solar System and Extra-Solar
System findings.
Summary
• Object size and orbit main criteria
• Historical context a consideration (Pluto is already on all of the plastic placemats!)
• Membership in a larger population will also be a consideration
• Object must be smaller than about 13 x’s Jupiter’s mass
For more information:
Discovery of UB 313:http://www.gps.caltech.edu/~mbrown/
First Discovery of Kuiper Belt Objects:http://www.ifa.hawaii.edu/faculty/jewitt/kb.html
List of planets orbiting other stars:http://exoplanet.eu
