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Astronomy 340 Fall 2007

Astronomy 340 Fall 2007. 27 November 2007 Class #23. Research Experience for Undergraduates. 10-12 weeks over the summer $3500-$4000 in salary plus travel, housing Applications typically due in late Dec – early Feb Transcript Statement of purpose/interest Letters of recommendation

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Astronomy 340 Fall 2007

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  1. Astronomy 340Fall 2007 27 November 2007 Class #23

  2. Research Experience for Undergraduates • 10-12 weeks over the summer • $3500-$4000 in salary plus travel, housing • Applications typically due in late Dec – early Feb • Transcript • Statement of purpose/interest • Letters of recommendation • http://www.nsf.gov/crssprgm/reu/list_result.cfm?unitid=5045

  3. Review & Announcements • Titan • Describe Titan’s atmosphere and possible source of methane • Other Moons • Compare and contrast the properties of the 4 Galilean satellites • What are the salient features of Saturn’s moon Enceladus? • Rings • What’s the Roche limit? How is it significant? • Compare and contrast the ring systems of the gas giants • Size distribution? Composition? Dynamics?

  4. Pluto - basics • Discovery • 1930 – Clyde Tombaugh (Lowell Obs) • Explain Neptune’s orbit? • Important Dates • 1976  CH4 ice, first estimate of diameter via albedo vs apparent brightness • 1978  6.4 day variation in brightness  discovery of Charon

  5. Pluto’s orbit

  6. HST view of Pluto

  7. Pluto Composition • Spectroscopy – CH4, N2, CO, H2O ices • Varied surface features • Compositional difference • Polar caps brighter • Darker equatorial  hydrocarbons? • Ice • Tenuous atmosphere from sublimation, but does it refreeze at 50 AU?

  8. Surface Composition - spectroscopy

  9. Atmosphere – how do you detect/measure Pluto’s atmosphere?

  10. Occultation

  11. Atmosphere • Detection via occultation • Structure seen in “kinks” in ingress and egress  variation over the years (is Pluto’s atmosphere expanding?) • Composition  primarily N2 • Pressure  few μbar

  12. Pluto’s Primary Moon Charon • Discovered as appendage to Pluto

  13. Pluto’s Primary Moon Charon • Discovered as appendage to Pluto • Orbit  highly inclined • Orbital/rotation axis lie ecliptic • System seen edge-on twice in 248 year orbit • Size (via occultation) • Mass ratio = 0.12 (Moon/Earth ~ 0.01) • Dcharon = ~ 1200 km (Pluto ~2300 km)

  14. Views of Pluto-Charon

  15. Giant Impact Origin?Canup 2005 Science 307 546 • Need to explain mass ratio/orbit • Collisions – similar to our moon • Numerical simulation show its possible! • Gravity • Compressional heating • Expansional cooling • Shock dissipation • 20000 – 120000 particles • Composition • Mg3Si2O5(OH)4 • Various mixtures of water ice (40-50%) and rock

  16. Canup – simulations of Pluto encounter

  17. Canup – SPH simulation including gravity, heating, cooling, shock dissipation • Ratio of impactor to total mass • Composition • Ratio of impact to escape velocity • Spin period • b’ = impact parameter • J = final angular momentum

  18. Pluto’s New Moons

  19. Orbits in Pluto-Charon system

  20. Pluto’s Moons • Charon • Semi-major axis = 19570 km • P = 6.3872 days • D = 1205 km • Nix • A = 48700 km • P = 25.5 days • D = 40 km • Hydra • A = 64800 km • P = 38.2 days • D = 160 km Collisional origin? What is the typical impact velocity of objects in the Kuiper Belt? What is the escape velocity for impact ejecta in the Pluto system? What implications can you draw from this?

  21. Pluto system formation

  22. New Horizons (http://pluto.jhuapl.edu) • Timeline • Jan 2006 – launch • Feb 2007 – jupiter encounter • Mar 2007 – June 2015 – “interplanetary cruise” • Jul 2015 – Pluto/Charon encounter • Science Objectives • Map surface composition of Pluto and Charon • Geology • Atmosphere – composition and escape rate • Surface temperatures • Similar studies of Kuiper Belt object

  23. Triton – composition & hemispheres

  24. TritonStern & McKinnon 2000 AJ 119 945 • Only large moon with retrograde orbit • Synchronously rotating (like our Moon)  has two distinct hemispheres • Leading side much more heavily cratered • High resurfacing rate (like Io, Europa) • Impact population from Kuiper belt • Lots of small impactors (< 1km) • Surface age ~ 100 Myr  volume resurface rate as high as Io, Europa • Geological/tectonic activity – possibly driven by tidal capture

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