Pluto is (still) not a planet. Prof. Richard Pogge OSU Department of Astronomy Science Café 2013 Sept 11

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1 Pluto is (still) not a planet. Prof. Richard Pogge OSU Department of Astronomy Science Café 2013 Sept 11

2 Fool: The reason the seven stars are seven is a pretty reason... Lear: Because they are not eight? Fool: Aye, indeed, thou wouldst make a good fool. William Shakespeare King Lear (1605)

3 The Solar System in 1766 Saturn Jupiter Earth Venus Mars Mercury

4 In 1766, Johann Titius noted that planet distances follow a simple geometric progression with a gap between Mars & Jupiter. a = m m = m V E M J S Johann Bode published what we now call the Titius-Bode Law in Johann Daniel Titius ( ) Johann Elert Bode ( )

5 William Herschel discovered the planet Uranus on 1781 March 13. NASA First new planet since antiquity, but it is not a naked-eye planet.

6 Uranus fits the Titius-Bode law! m V E M J S U Where was the missing planet between Mars & Jupiter?

7 In 1799, Baron Franz Xaver von Zach organized 24 astronomers into the Celestial Police. Their charge: To make a systematic search for the "missing" 5 th planet between Mars and Jupiter predicted by the Titus-Bode Law. Baron Franz Xaver von Zach ( )

8 Giuseppe Piazzi discovered Ceres on Jan 1, 1801 while looking for the "missing" star Mayer 87. Giuseppe Piazzi ( ) Hubble Space Telescope

9 Ceres was right where the Titius-Bode Law said it should be. m V E M c J S U But, things soon got complicated...

10 Heinrich Olbers discovered Pallas on May 28, 1802 while observing Ceres. Hubble Space Telescope Heinrich Wilhelm Matthäus Olbers ( ) New problem: Pallas and Ceres orbits crossed!

11 In 1802, William Herschel coins the term "asteroid" ("star-like"), rejecting the idea these are new planets. They are very much smaller than the other planets. Their orbits are more tilted and elliptical than the other planets. Ceres & Pallas cross each other s orbits. Bristol City Museum & Gallery

12 By 1807, 4 new "planets" had been discovered in the space between Mars & Jupiter Vesta: 1807 (Olbers) Ceres: 1801 (Piazzi) Juno: 1807 (Harding) Vesta (NASA/Dawn) Then nothing for 38 years... Pallas: 1802 (Olbers)

13 The discovery of Neptune in 1846 was a factor in reclassifying Ceres, Pallas, Juno, and Vesta as "Minor Planets. Urban Leverrier Johann Galle Predicted mathematically by Leverrier and Adams from the orbital wobble of Uranus. Found by Galle at Leverrier s predicted position. Violates the Titius-Bode law by 30% (closer than predicted ).

14 Wealthy amateur Percival Lowell began a search for a planet beyond Neptune in It was expected from residual wobbles in Uranus and Neptune s orbits. Built a private observatory in Flagstaff, AZ. Actually photographed Pluto twice but didn't notice it. Percival Lowell ( )

15 Pluto was discovered photographically by Clyde Tombaugh on February 18, Clyde Tombaugh at the Lowell Blink Comparator Lowell "Pluto" Astrograph

17 The new planet was named Pluto, and became immediately controversial. It is too small to cause orbit wobbles in Uranus or Neptune. Its orbit is highly tilted and elliptical. Its orbit crosses the orbit of Neptune. But, nobody questioned that it was a planet...

18 Pluto Neptune

19 Pluto is a tiny, cold, icy world orbiting far from the Sun. Temperatures: 378 to 396º F Rocky core over an icy mantle. Surface is covered with frozen gases. Has a thin nitrogen atmosphere.

20 Pluto has 1 large moon (Charon) and 4 smaller moons. Hubble Space Telescope

21 Pluto is smaller than our Moon. Pluto and its large moon Charon have the largest parent-to-moon mass ratio in the Solar System.

22 In the 1950s, Edgeworth and Kuiper predicted the existence of a large population of small icy bodies beyond the orbit of Neptune. The first discovered in 1992 by Jewitt & Luu. Hundreds more were found by the early 2000s. All are smaller than Pluto, but many have similar orbital characteristics.

23 We now call this the Kuiper Belt Flattened belt of icy objects between 30 and 50 AU from the Sun (from Neptune s orbit to beyond Pluto). JHU/APL

24 In January 2005, Brown, Trujillo, and Rabinowitz discover 2003UB 313 and set off a controversy. It is about the same size as Pluto. It has a very elliptical & tilted orbit It has a Pluto-like composition. It has 1 moon, resulting in a mass a little larger than Pluto s. Was it the 10 th planet? Mike Brown Chad Trujillo David Rabinowitz

25 The group's codename for the new object was "Xena"

26 The official name chosen was Eris The goddess of discord

28 In August 2006, the IAU took up the question of how to define a planet. 1.Orbits around the Sun and is not a satellite. 2.Shaped by Gravity: sufficient mass to assume a spheroidal shape. 3.Has cleared its orbital neighborhood ("orbital dominance") Three Dwarf Planets: Ceres, Pluto, & Eris

29 The Solar System in September 2013 Gas Giants Terrestrials Ice Giants Dwarf Planets

30 The Terrestrial Planets are the rocky planets found in the inner Solar System AU from the Sun. Mercury (0.055 M E ) Venus (0.82 M E ) Earth (1 M E ) Mars (0.11 M E ) Composed of mostly Silicates and Iron with solid surfaces All are High Density: g/cc (rock & metal)

31 Jupiter & Saturn are Gas Giants with thick Hydrogen & Helium atmospheres over rock & ice cores Jupiter: 318 M E 11.2 R E Saturn: 95.2 M E 9.44 R E

32 Uranus and Neptune are Ice Giants made mostly of ices with thin Hydrogen & Helium atmospheres. Uranus Neptune 14.5 M E 4.01 R E 17.1 M E 3.88 R E

33 The Dwarf Planets Pluto Eris Makemake Ceres Haumea 40+ other candidates Moon Earth

38 The most controversial and least well-defined criterion is orbital dominance. The "One planet per orbit" rule. Examples: 1. Anything near Earth has its orbital altered by the gravitational influence of Earth. 2. Ceres and Pallas have orbits that cross, so neither "dominates" its orbit. 3. Pluto is in a 3:2 resonance with Neptune, and its motion is dominated by Neptune.

40 Planet Clears its orbit quickly compared to age of the Solar System Dwarf Not enough time to have cleared its orbit

41 Pluto and Eris are the largest of a new family of Trans-Neptunian Objects. More than 1000 known today. Could be as many as ~70,000 more than 100 km in diameter. The largest are >1000 km in diameter. Total combined mass could be 2% to 4% the mass of Earth. Icy material leftover from the formation of the Solar System

43 The New Horizons mission was launched in 2006 to study Pluto and the Kuiper Belt up close. Launch: January 19, 2006 Pluto fly-by: July 14, 2015 Explore Kuiper Belt Pluto & Charon, July 2013

44 New Horizons at Pluto

45 Further Reading: The Pluto Files Neil degrasse Tyson How I Killed Pluto and Why it Had it Coming Mike Brown (see pages )

Planets and Dwarf Planets by Shauna Hutton

Planets and Dwarf Planets by Shauna Hutton Name: Wow! Technology has improved so well in the last several years that we keep finding more and more objects in our solar system! Because of this, scientists have had to come up with new categories