1. General Astronomy The Solar System The Dwarf Planets

2. Defining a Planet A dwarf planet is a celestial body that –is in orbit around the Sun, –has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, –has not cleared the neighborhood around its orbit, and –is not a satellite.

3. Ceres

4. On January 1, 1801, Piazzi (a Sicilian astronomer) noted a new object which he watched until February 11. He wrote Bode of his discovery, but by the time Bode looked for it, the object was too near the direction of the Sun for observation. In November, Gauss predicted the location of this object based on Piazzi's observations; it was found on Dec 31, 1801 Piazzi named the object "Ceres" after the protecting goddess of Sicily The missing planet had been found at a distance of 2.77 AU

5. Ceres By 1890, over 300 more "planets" had been discovered in the same region (in regards to distance from the Sun) and Ceres was stripped of its planetary status. In 2006, Ceres was given a new designation of "dwarf planet"

6. Ceres

7. Ceres’ Statistics Eccentricity0.080 Orbital period4.6 yr Orbital Radius2.7 AU Inclination10.6° Size975×909 km Mass9.5×10 20 kg Density2.08 g/cm³ Escape velocity0.51 km/s Rotation0.3781 d Tilt of Axis~4 ° Albedo0.113 Mean surface temperature~167 K Max surface temperature239 K (-34 ° C)

8. Ceres’ Interior

9. Ceres versus the Moon

10. Pluto

11. Eccentricity0.249 Orbital period248 years Orbital Radius39.5 AU Inclination17.14 ° Size2274 Km Mass9.5×10 20 kg Density2.06 g/cm³ Escape velocity1.2 km/s Rotation6.4 d Tilt of Axis119.6 ° Albedo 0.49–0.66 (varies by 35%) Mean surface temperature44 K Max surface temperature55 K DiscovererClyde Tombaugh, 1930

12. Pluto

15. Charon

17. Nix and Hydra Two additional moons of Pluto were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005. These small moons orbit Pluto at approximately two and three times the distance of Charon –Nix at 48,700 Km –Hydra at 64,800 Km from the barycenter of the system. They have nearly circular prograde orbits in the same orbital plane as Charon Observations of Nix and Hydra are ongoing to determine individual characteristics. –Hydra is sometimes brighter than Nix, speculating that it either is larger in dimension or different parts of its surface may vary in brightness. Sizes are estimated from albedos. The moons' spectral similarity with Charon suggests a 35% albedo similar to Charon's –this results in diameter estimates of 46 kilometers for Nix and 61 kilometers for brighter Hydra. –Upper limits on their diameters can be estimated by assuming the 4% albedo of the darkest Kuiper Belt objects; these bounds are 137 ± 11 km and 167 ± 10 km respectively. –At the larger end of this range, the inferred masses are less than 0.3% of Charon's mass, or 0.03% of Pluto's.

18. Pluto’s newest moons (2011 and 2012)

19. Eris and Dysnomia

20. Eris

21. Eris (2003 UB313) Eccentricity0.438 Orbital period557 years Orbital Radius38.2 – 97.6AU Inclination44° Size2400 Km Mass? Density? Escape velocity? Rotation> 8 h Tilt of Axis? Albedo0.86 Mean surface temperature~ 30 K DiscovererChad Trujillo, Dave Rabinowitz and Mike Brown, 2002

23. Makemake

24. Makemake is the creator of humanity in the mythos of Rapa Nui It is the third-largest known dwarf planet in the Solar System No satellites have been detected around Makemake so far The presence of methane and possibly nitrogen suggests that Makemake could have a transient atmosphere

25. Makemake Orbital characteristics Aphelion53.1 AU Perihelion38.5 AU Semi-major axis45.8 AU Eccentricity0.159 Orbital period309.88 yr Average orbital speed4.4 km/s Inclination28.96° Physical characteristics Dimensions1300–1900 km Mean radius750 km Mass~4 × 10 21 kg Mean density~2 g/cm³ Sidereal rotation period unknown Axial tiltunknown Albedo78.2 Temperature30–35 K Apparent magnitude16.7

26. Haumea

27. The goddess of childbirth and fertility in Hawaiian mythology. –The name is particularly apt as the goddess Haumea also represents the element of stone and observations of Haumea hint that, unusually, the dwarf planet is almost entirely composed of rock with a crust of pure ice. Haumea is joined in its orbit by two satellites that are thought to have been created by impacts with it in the past. –The first and largest moon is to be called Hi'iaka, after the Hawaiian goddess, the patron goddess of the island of Hawai'i. –The second moon of Haumea is named Namaka, a sea goddess, also Haumea's daughter

28. Haumea Orbital characteristics Aphelion51.5 AU Perihelion35.2 AU Semi-major axis43.3 AU Orbital period285.4 yr Inclination28.2° Satellites2 Eccentricity0.188 Physical characteristics Dimensions~1960 × 1518 × 996 Km Mass4.2 ×10 21 kg Mean density2.6–3.3 g/cm³ Rotation period3.9 hr Albedo0.7 Temperature32K Apparent magnitude17.3

29. Makemake Haumea Pluto

30. Other Candidates

31. Quaoar

32. Distance from Sun = 50 AU Orbital period = 285 years Eccentricity = 0.04 Diameter = 1250 Km Orbital Inclination = 8° Discoverers: Chad Trujillo and Mike Brown, 2002

33. Sedna

34. Sedna (2003 VB12) Distance from Sun: 74 AU - 990 AU Length of day:10 hours Orbital period:~11,249 years Eccentricity: 0.849 Diameter: 1800 Km Discoverers: Chad Trujillo, Dave Rabinowitz and Mike Brown Year of Discovery: 2002

35. Sedna

36. EasterbunnySanta Makemake Haumea