Pluto: the next decade of discovery

Leslie YoungSouthwest Research Institute

layoung@boulder.swri.edu

I. Decade-scale surface-atmosphere interaction

2005: 30.9 AU, 34° sub-solar lat2015: 32.8 AU, 49° sub-solar latFarther at 0.2 AU/year distance,More northerly at 1.5 °/year.

30 35 40 45 50

20202030

Distance from Sun (AU)

1990 20002010

20702080

209021002110

0.001 0.01 0.1 1 10 100

Radio occultation observableN2 α-β transition

40 ( . 2004) K Tryka et al

UVS occultation observable

Global atmosphere

Stellar occultationobservable

( )Surface Temperature K

( )Surface Pressure µbar

01234567

1850 1900 1950 2000 2050 2100 2150year

2005-2015, distance increases by 6%, insolation decreases by 12%. Simplest models have temperature decreasing by 3% (~1.2K),for the pressure nearly halving.

Sicardy et al. 2003, Nature 424

Elliot et al. 2003, Nature 424

perihelion

Hansen and Paige fig 3 (high thermal inertia)

Hansen and Paige 1996, Icarus 120

1000 1200year

Hansen and Paige fig 4 (moderate thermal inertia)

perihelion

1000 1200year

Hansen and Paige fig 7 (low thermal inertia)

perihelion

1000 1200year

Darkening of ices following sublimation Thermal inertiaOld, frost-covered winter pole coming into sunlight

II. Distinguishing seasonal models with observations

Changes in lightcurve mean and amplitude can be due to volatile transport or changing viewing.

15.60 0.2 0.4 0.6 0.8 1

phase (0.75-East Longitude/360))

Stern et al. 1988, Icarus 75Buie et al. 1997, Icarus 125 1992/93

1982.2

1975.2

1964.4

1954.8

Douté et al 1999, Icarus 142

Spectra on the surface absorption in reflected sunlight is diagnostic of the volatiles on Pluto's surface, including their grain size, mixing state, and temperature. 0.8-2.5 µm range includes N2, CH4, and CO. Shorter wavelengths include weak CH4 bands, and CH4 and tholins have absorption at 3.3 µm (See Olkin 55.02).

1000 1200year

N2 frost temperature

60 µm brightness temperature1300 µm brightess temperature

Hansen and Paige 1996, Icarus 120

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Occultations are the most sensitive and direct measure of changes in atmospheric pressure.

Young 2004, BAAS

2005 Jul 11 03:36:14 UTC313.2 (Sicardy 49.05, Young 55.04, Gulbis 55.05)

2006 Jun 12 16:21:49 UTP384.2

2006 Oct 31 2:30:29 UTP415

2007 May 12 4:42:24 UTP456

III. Some words of warning...

Young et al. 2001, AJ 121

Grundy & Buie 2001, Icarus 153

Young 55.03, Buie 49.03

2006 2007 2008 2009 2010Date

Non-secular time-dependent effects on visible albedo—rotation and possible opposition surges

Longitudinal change is much larger than the tentative secular variation (green vs. red dots) in CH4 1.66 µm band

Grundy and Buie 2001,Icarus 153.

Lellouch et al. 2000, Icarus 147

Thermal rotational lightcurves have higher amplitudes thanthe expected seasonal change.

.6 Jy .6 Jy

IV. New Horizons spacecraft to Pluto; flight 2006-2015

PERSI Remote Sensing Package

Objectives:MVIC: Global geology and geomorphology. Stereo and terminator images. Refine radii and orbits. Search for rings and satellites. Search for clouds and hazes.LEISA: Global composition maps, high resolution composition maps, temperatures from NIR bands.ALICE: UV airglow and solar occultation to characterize Pluto’s neutral atmosphere. Search for ionosphere, H, H2, and CxHy. Search for Charon’s atmosphere.

REX Radio Experiment

Objectives:•Profiles of number density,temperature, and pressure inPluto ’s atmosphere, includingconditions at surface.•Search for Pluto’s ionosphere.•Search for atmosphere andionosphere on Charon.•Measure masses and radii ofPluto and Charon, and massesof flyby KBOs.•Measure disk- averagedmicrowave brightnesstemperatures (4.2 cm) ofPluto and Charon.

SWAP Solar Wind Plasma Sensor

Objectives:•Slowdown of the solar wind,as a diagnostic of Pluto’s atmospheric escape rate.•Solar wind standoff•Solar wind speed•Solar wind density•Nature of interaction of solar wind and Pluto’s atmosphere (distinguish magnetic, cometary, and ionospheric interactions)

PEPSSI Pluto Energetic Particle Spectrometer

Objectives:•Measure energetic particles from Pluto’s upper atmosphere,as a diagnostic of Pluto’s atmospheric escape rate.

LORRI Long Range Reconnasance Imager

Objectives• Far-side maps• High-resolution closest approach images, including terminator and stereo imaging.

Summary

• We expect Pluto to undergo seasonal change in the next decade

• Observations can constrain models of voalatile transport in the outer solar system

• Beware spatial-temporal confusion!• Long time-base observations support

and are supported by the planned New Horizons mission to Pluto

Pluto: the next decade of discovery

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