Pluto & Friends - Outline

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1 Pluto & Friends - Outline Discovery of Pluto Characteristics of Pluto Characteristics of Charon Pluto s Downfall as a Major Planet Large Kuiper Objects The IAU Resolution

2 Discovery of Pluto Another planet required to account for apparent perturbations in the orbits of Uranus & Neptune Unsuccessful attempts were made by Percival Lowell to find an additional planet Finally discovered in 1930 by Clyde Tombaugh using a newly developed wide-field camera at the Lowell Observatory Pluto was named after the Roman god of the underworld, and Charon (Pluto s moon) was named after the mythical boatman who carried the dead into the realm of Pluto

3 Discovery Photographs (Note - new techniques & instrumentation drive a lot of ground-breaking science) Clyde Tombaugh. 65% of the sky photographed & thousands of hours logged over a 10-month period leading up to the discovery of Pluto

4 Properties of Pluto Atmosphere: Nitrogen & other gases that sublimate from the surface Average Distance from the Sun: 5.5 light hours (39.5 AU) Rotation Rate: 6.4 Earth days Orbital Period: 248 Earth years Axis Tilt: 118 Number of Moons: 3

5 Orbital Inclination = 17 Pluto s Orbit Orbital Eccentricity = 0.25 For a circular orbit, Eccentricity = 0.0 Mercury s Eccentricity = 0.21 Aphelion = 49.3 AU; Perihelion = 29.3 AU Effect! sublimation & refreshing of volatiles on the surface of Pluto Axis Tilt = 118 Axis Tilt of Uranus = 98

6 Pluto s orbit Relative to the Other Planets

7 Map of the Surface of Pluto Mass = 0.25% Earth s Mass Density = 2.1 g cm -3 Surface: Reflectivity ~ 30-50% Methane Ice! Bright Spots??! Dark Spots

Charon - 1978 discovery Mass = 10% Pluto s Mass (M moon = 1.25% M earth ) Density = 1.

8 Charon discovery Mass = 10% Pluto s Mass (M moon = 1.25% M earth ) Density = 1.6 g cm -3 (a bit low) Surface = water ice Charon s orbital period is equal to Pluto s rotation period Formation? Similar to the formation of the Moon, which explains densities

9 Charon s Orbit

10 Standing on the Surface of Pluto The sky would be black The sun would be 1600 times fainter than from the Earth Charon would loom motionless in the sky with an angular diameter 10 times that of the Moon as viewed from the Earth

11 2005 Announcement of 2 new moons of Pluto Designated - S/2005 P1 and S/2005 P2 5,000 times fainter than Pluto

12 New Horizons. The Mission: To map the surface composition & temperature of Pluto & Charon To characterize the geology & morphology of Pluto & Charon To characterize the neutral atmosphere & escape rate To search for rings & additional satellites To conduct similar investigations of one or more KBOs

13 Trajectory & Present Location

14 September 21-24, First View of Pluto by New Horizons

15 Pluto & its moon(s) probably resemble - The nuclei of comets (ala Tempel) & Neptune s moon Triton (discussed later)

16 Brief Review - Oort Cloud & Kuiper Belt Long Period Comets Random Inclinations (Oort Cloud) Short Period Comets Low Inclinations (Kuiper Belt)

17 The First KBO Discovered in 1992 D. Jewitt & J. Luu Large field of view CCD Images

18 Origin of the Kuiper Belt Planetesimals whose accretion was disrupted by the formation of Neptune Neptune stirred up the motions of KBO, causing more collisions

19 Formation of KBOs & Comets

20 Kuiper Belt Orbits

21 Pluto s Downfall as a Major Planet Plutinos

22 Pluto s Downfall

23 But Pluto has at least one moon! Pluto & Charon KBO So do some KBOs.

24 Large KBOs: (1) Varuna Discovered in 2000 by McMillan (Spacewatch) Size ~ 1060 km in diameter (I.e., 40% of Pluto s diameter) Orbital Period ~ 283 years Distance ~ AU from Sun Inclination ~ 17 degrees

25 Size of Varuna compared to other solar system objects

26 How are Sizes of these Distant Objects Distance to object Determined? Measure of reflected solar light Measure of albedo based on comparing optical (reflected) & thermal (absorbed & reradiated as heat) submillimeter-wave light + some other assumptions

27 Albedo vs. Size Pluto Charon Varuna

28 (2) Quaoar Discovered in 2002 by Trujillo & Brown Size ~ 1250 km in diameter Orbital Period ~ 285 years Orbit has low eccentricity, with an inclination of 8 degrees & a Sun-Quaoar distance of ~ 43.3 AU.

29 Size of Quaoar compared with other solar system objects

30 Orbit of Quaoar

31 (3) Sedna Discovered in 2004 by Brown, Trujillo, & Rabinowitz Size < 1800 km in diameter Orbital Period ~ 10,500 years Orbit is extremely elliptical, with a closest approach of 76 AU First Discovered Oort Cloud Object??

32 Rough Size of Sedna compared to other solar system objects

33 Zooming out to the Orbit of Sedna Video

(4) 2003 UB313 - aka The 10th Planet Discovered in 2003 by Brown, Trujillo, & Rabinowitz Size > 2210 km in diameter, I.e., equal to or larger than Pluto in size Orbital Period ~ 560 years Perihelion ~ 38 AU, Aphelion ~ 97 AU Inclination ~ 44 degrees!

34 (4) 2003 UB313 - aka The 10th Planet Discovered in 2003 by Brown, Trujillo, & Rabinowitz Size > 2210 km in diameter, I.e., equal to or larger than Pluto in size Orbital Period ~ 560 years Perihelion ~ 38 AU, Aphelion ~ 97 AU Inclination ~ 44 degrees!! How did such a massive object get so far off the plane of the solar system??

35 Orbit of 2003 UB313

36 Spectrum of 2003 UB313 - similar to that of Pluto

37 2003 UB313 appears to have a moon Moons are quite commonplace

38 Large Objects Continue to be 75% Pluto size Period ~ 307 yr Distance ~ AU from Sun Inclination ~ 29 degrees Discovered 75% Pluto size Period ~ 285 yr Distance ~ AU from Sun Inclination ~ 28 degrees

39 IAU Resolution on Pluto: The Triggers The similarities in the properties of Pluto & the KBOs (mainly the Plutinos) The exhibit at the Hayden Planetarium in 2001 which showed that there are only 8 planets The discovery of KBOs comparable to Pluto in size

40 This is a messy issue politically The public has been told for many years Pluto is a planet Tombaugh s family clearly does not want Pluto demoted The UB313 discoverers would like to be credited for discovering the 10th planet The team involved in the New Horizons mission to Pluto (launched January 2006) do not want Pluto demoted But there is also a desire (among the public and some scientist) to have an exact definition of a planet. The definition must please the public and the scientific community

Pluto Data: Numbers. 14b. Pluto, Kuiper Belt & Oort Cloud. Pluto Data (Table 14-5)

Pluto Data: Numbers. 14b. Pluto, Kuiper Belt & Oort Cloud. Pluto Data (Table 14-5) 14b. Pluto, Kuiper Belt & Oort Cloud Pluto Pluto s moons The Kuiper Belt Resonant Kuiper Belt objects Classical Kuiper Belt objects Pluto Data: Numbers Diameter: 2,290.km 0.18. Earth Mass: 1.0. 10 22 kg