1. Planet Searching After Uranus and Neptune, some began searching for yet another planet, among them was P. Lowell from 1905-1916 Search resumed in 1929 by C. Tombaugh, who identified a candidate on 2/18/1930 The name “Pluto” was suggested by an English girl of age 11.

2. Discoveries: Pluto at left and moon Charon at right Clyde Tombaugh James Christy

3. Hubble Image of Pluto & Charon

4. Pluto and Charon to Scale

5. Mapping Pluto Charon’s orbit is such as to eclipse Pluto at times, allowing us to map its surface Done in 1985 HST mapped Pluto to a resolution of 150 km, revealing a strong variation of reflectivity

6. Pluto-Charon Eclipses

7. Charon-Pluto Eclipse Visual

8. Surface Mapping with HST

9. A Map of Pluto

10. Pluto is ODD! Similar to Triton Cold at T=50K Has frozen CH 4 Mostly rock and ice Largest eccentricity, with D ~ 30-50 AU (sometimes closer than Neptune) Large orbital inclination Smaller than planets Large moon in relative size Origin of Pluto-Charon: Pluto ejected from Neptune – problem is Charon Pluto and Charon formed together (?) Pluto captured Charon (?) Giant impact like Earth- Moon system (?)

11. Orbits for Pluto and Neptune

12. Atmosphere of Pluto It is possible to study Pluto’s atmosphere from Earth using occultation of starlight. The light passes through the tenuous atmosphere. In this way we can “see” the atmosphere.

13. Spectroscopy reveals composition of Pluto and Charon

14. Charon Discovered in 1978 by J. Christy Has an icy surface of frozen N and tenuous CH 4 atmosphere Orbital plane is nearly perpendicular to ecliptic In synchronous orbit with Pluto (and vice versa) Ratio of masses: M C /M P =0.13 Ratio of sizes: R C /R P =0.51 As seen from Pluto, Charon subtends an angle of 4 o, but the Sun is only 1’ !

15. Structure of Pluto and Charon

16. Synchronous Orbits for Pluto and Charon

17. New Moons: Nix, Hydra, and “P4”

18. New Horizons

19. Dwarf Planets A "dwarf planet" is a celestial body that, within the Solar System: 1. is in orbit around the Sun 2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a (near-spherical) shape 3. has not cleared the neighborhood around its orbit 4. is not a satellite The term "dwarf planet" applies only to objects in the Solar System and is distinct from "planet" and "small solar system body".

20. Eris and moon Dysnmonia (goddess of discord and daughter of lawlessness) Gabrielle Xena

21. Orbit of Eris

22. Comparison of Pluto with Eris

23. Ceres Ceres is now a dwarf planet that was previously the largest of the asteroids. It was discovered on Jan 1, 1801, by Giuseppe Piazzi. With a diameter of about 950 km. Ceres is in the asteroid belt, and it was the largest and most massive body there, but now is the 3rd of the dwarf planets. Interestingly, it contains approximately a third of the belt's total mass.

25. Rotation and Surface of Ceres

26. Interior of Ceres

27. Two Other Dwarf Planets Haumea Makemake

28. Future Dwarf Planets?