Astronomy 340 Fall 2007
27
27 NOVEMBER 2007 CLASS #23 Astronomy 340 Fall 2007
description
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 - PowerPoint PPT Presentation
Transcript of Astronomy 340 Fall 2007
27 NOVEMBER 2007CLASS #23
Astronomy 340Fall 2007
Research Experience for Undergraduates
10-12 weeks over the summer$3500-$4000 in salary plus travel, housingApplications 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
Review & Announcements
Titan Describe Titan’s atmosphere and possible source of
methaneOther 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?
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
Pluto’s orbit
HST view of Pluto
Pluto Composition
Spectroscopy – CH4, N2, CO, H2O icesVaried surface features
Compositional difference Polar caps brighter Darker equatorial hydrocarbons?
Ice Tenuous atmosphere from sublimation, but does it
refreeze at 50 AU?
Surface Composition - spectroscopy
Atmosphere – how do you detect/measure Pluto’s atmosphere?
Occultation
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
Pluto’s Primary Moon
Charon Discovered as
appendage to Pluto
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)
Views of Pluto-Charon
Giant Impact Origin?Canup 2005 Science 307 546
Need to explain mass ratio/orbitCollisions – similar to our moonNumerical 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
Canup – simulations of Pluto encounter
Canup – SPH simulation including gravity, heating, cooling, shock dissipation
Ratio of impactor to total mass
CompositionRatio of impact to
escape velocitySpin periodb’ = impact
parameterJ = final angular
momentum
Pluto’s New Moons
Orbits in Pluto-Charon system
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?
Pluto system formation
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
Triton – composition & hemispheres
TritonStern & McKinnon 2000 AJ 119 945
Only large moon with retrograde orbitSynchronously 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
