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Astronomy 340 Fall 2005

Astronomy 340 Fall 2005. 22 November 2005 Class #23. Review & Announcements. Titan Describe Titan’s atmosphere Rings What’s the Roche limit? How is it significant? Compare and contrast the ring systems of the gas giants Size distribution? Composition? Dynamics?. Pluto - basics.

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Astronomy 340 Fall 2005

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  1. Astronomy 340Fall 2005 22 November 2005 Class #23

  2. Review & Announcements • Titan • Describe Titan’s atmosphere • Rings • What’s the Roche limit? How is it significant? • Compare and contrast the ring systems of the gas giants • Size distribution? Composition? Dynamics?

  3. 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

  4. Pluto’s orbit

  5. HST view of Pluto

  6. 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?

  7. Surface Composition - spectroscopy

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

  9. Occultation

  10. 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

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

  12. 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)

  13. Views of Pluto-Charon

  14. 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

  15. Canup – simulations of Pluto encounter

  16. 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

  17. Pluto’s New Moons • S/2005 P1, S/2005 P2 • Discovered via HST • Separation ~ 27,000 km, diameters 64, 200 km) • Don’t know much else about them!!

  18. Orbits in Pluto-Charon system

  19. 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

  20. Triton – composition & hemispheres

  21. 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

  22. Cratering Density

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