2 7 N O V E M B E R 2 0 0 7

C L A S S # 2 3

Astronomy 340Fall 2007

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

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?

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 ices

Varied 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/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

Canup – simulations of Pluto encounter

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

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 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