The Solar System Missions

Comparative Planetology * The study of the similarities and dissimilarities of the constituents of the solar system. * Provides a basis for understanding how the solar system might have formed and how it evolved.

planets not shown to scale >> MercuryVenusEarthMarsJupiterSaturnUranusNeptunePluto Mean Distance from the Sun (AU) Sidereal period of orbit (years) Mean Orbital Velocity (km/sec) Orbital Eccentricity Inclination to ecliptic (degrees) Equatorial Radius (km) Polar Radius (km)same same Mass of planet (Earth=1) Mean density (grams/centimeter³ ) Body rotation period (hours) Tilt of equator to orbit (degrees) Number of observed satellites0012>

Comparative Planetology * The study of the similarities and dissimilarities of the constituents of the solar system. * Provides a basis for understanding how the solar system might have formed and how it evolved. Knowledge has grown enormously as a result of space missions.

Comparative Planetology Terrestrial Planets – Terra – Earth-like *High Density*Closer to sun *Small*Slow rotation *Few moons*Close spaced orbits *Small mass*Rocky *Weak magnetic fields*Solid surface *No rings Jovian Planets – Jupiter – Jupiter-like *Low Density*Farther from sun *Large*Fast rotation *Many moons*Wide spaced orbits *Large mass*Gaseous *Strong magnetic fields*No solid surface *Rings

Comparative Planetology - Pluto Terrestrial Planets – Terra – Earth-like *High Density*Closer to sun *Small*Slow rotation *Few moons*Close spaced orbits *Small mass*Rocky *Weak magnetic fields*Solid surface *No rings Jovian Planets – Jupiter – Jupiter-like *Low Density*Farther from sun *Large*Fast rotation *Many moons*Wide spaced orbits *Large mass*Gaseous *Strong magnetic fields*No solid surface *Rings

What’s New?? NEW YORK (AP) -- One of the nation's leading science museums has quietly shaken up the universe by suggesting that Pluto is not necessarily a planet at all but just a lump of ice. The startling suggestion comes from scientists at the Rose Center for Earth and Space, which opened last year at the American Museum of Natural History in New York.

Comparative Planetology - Pluto Definition of a Planet in the solarsystem (2006, Interantional Astronomical Union (IAU)) 1. The object must be in orbit around the sun 2. The object must has sufficient mass that it assumes a hydrostatic equilibrium (nearly round) shape. 3. The object must have “cleared the neighborhood” around its orbit. * A body fulfilling 1. and 2. only is classified as a Dwarf Planet. * A body fulfilling 1. only is classified as a Small Solar System Body (SSSB).

Comparative Planetology - Pluto Definition of a Planet in the solarsystem (2006, Interantional Astronomical Union (IAU)) 1. The object must be in orbit around the sun 2. The object must has sufficient mass that it assumes a hydrostatic equilibrium (nearly round) shape. 3. The object must have “cleared the neighborhood” around its orbit. * A body fulfilling 1. and 2. only is classified as a Dwarf Planet. * A body fulfilling 1. only is classified as a Small Solar System Body (SSSB). Pluto does not meet criterion 3. and has been classified as a Dwarf Planet

American Dialect Society “Plutoed” Voted 2006 Word of the Year In its 17th annual words of the year vote, the American Dialect Society voted “plutoed” as the word of the year, in a run-off against climate canary. To pluto is to demote or devalue someone or something, as happened to the former planet Pluto when the General Assembly of the International Astronomical Union decided Pluto no longer met its definition of a planet. ADS Press Release Friday, January 5, 2007

International Astronomical Union Reclassification 2008 But… In June 2008, the International Astronomical Union (IAU) introduced the word “Plutoid” as the name for objects like Pluto.

"Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit." International Astronomical Union Reclassification 2008

Comparative Planetology - Pluto Definition of a Planet in the solarsystem (2006, Interantional Astronomical Union (IAU)) 1. The object must be in orbit around the sun 2. The object must has sufficient mass that it assumes a hydrostatic equilibrium (nearly round) shape. 3. The object must have “cleared the neighborhood” around its orbit. A body fulfilling 1. and 2. only and lying inside the orbit of Neptune is classified as a Dwarf Planet. * A body fulfilling 1. and 2. only and lying outside the orbit of Neptune is classified as a Plutoids. * A body fulfilling 1. only is classified as a Small Solar System Body (SSSB). Pluto does not meet criterion 3. and has been classified as a Plutoid

It isn’t over Some groups are resisting the demotion of Pluto from planet status, and are also resisting the introduction of the term “Plutoid” International Astronomical Union Reclassification 2008

It isn’t over On February 26, 2009, the Illinois state senate voted unanimously “that March 13, 2009 (A Friday the 13 th ), be declared “Pluto Day” in the State of Illinois in honor of the date its discovery was announced in 1930.” Note: Pluto’s discover was Clyde Tombaugh, who was born and raised in Streator, Il. International Astronomical Union Reclassification 2008

It isn’t over Society for the Preservation of Pluto as a Planet International Astronomical Union Reclassification