Presentation Topic Goes Here

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ATMOSPHERESREPORTPEP MeetingMay 11,
2007Randy Gladstone, ATM LeadMike Summers, ATM
Deputy Lead
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Overview

• Review Group 1 2 Requirements related to the
  Atmospheres Theme (there are no Group 3
  Requirements related to the Atmospheres Theme)
• Discuss how each Requirement will be met (current
  knowledge, expected value, and NH capability)
• Discuss best overall encounter date

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Atmospheres Requirements
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Level 1 Requirements

• 1.3a Composition Determine the mole fractions of
  N2, CO, CH4 and Ar in Plutos atmosphere to at
  least the 1 level of the total mixing ratio.
• Method EUV/FUV solar occultation (primary)
• EUV/FUV airglow (secondary)
• Current Knowledge f(N2) 0.95-0.99
• f(CH4) 0.01-0.03 Young et al. 1997
• f(Ar) lt ?
• f(CO) lt ?
• Expectation f(N2) 0.95-0.99
• f(CH4) 0.01-0.03
• f(Ar) lt 0.05 Max. expected based on
  cosmochemistry
• f(CO) 0.0005 From photochemical models
• Capability f(N2) gt 0.03 Solar occultation
• f(CH4) gt 1E-5 Solar occultation
• f(Ar) gt 0.1 Airglow
• f(CO) gt 6E-3 Airglow

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Model Solar Occultation Airglow
Opacity
Solar Flux
Flux (photons/cm2/s/nm)
Tangent Altitude (km)
Airglow
Alice Count Rates
Count Rate (counts/s/nm)
Model Brightness (R)
Wavelength (nm)
Wavelength (nm)
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Nominal Pluto Solar Occultation
Ingress Range 38,169 km Sun subtends 5.4 km
at Pluto
Egress Range 47,077 km Sun subtends 6.7 km at
Pluto
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Level 1 Requirements

• 1.3b Thermospheric thermal structure Measure T
  and dT/dz at 100 km vertical resolution to 10
  accuracy at gas densities of 109 cm-3 and higher.
  
• Method EUV/FUV solar occultation
• Current Knowledge T? 100 K
• dT/dz 2-3 K/km (but only in boundary layer)
• Expectation Steep rise from surface
• Peak near z100km
• Mild falloff above that due to expansion
  cooling
• Capability Measure N2 profile for z1000-2000
  km (10 scale heights)
• Measure CH4 profile for z500-1000 km (3
  scale heights)

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Level 1 Requirements

• 1.3c Aerosols Characterize the optical depth and
  distribution of near-surface haze layers over
  Plutos limb at a vertical resolution of 5 km or
  better.
• Method Visible imaging (primary)
• FUV solar occultation (secondary)
• Current Knowledge None
• Expectation Triton-like geysers? Photochemical
  Haze?
• Capability Imaging of nightside hazes
  silhouetted by Charon
• (MVIC resolution 0.3 km)
• Imaging of bright limb at high phase angle
• (MVIC resolution 2 km)
• Longest wavelengths of the solar FUV
  occultation should reach
• the ground before becoming optically thick
  (gt180 nm)

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Charon Silhouette of Nightside Hazes
Range 12,571 km (7 minutes before C/A) Charon
subtends 472 km along Pluto limb Nominal Flyby
only!
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Level 1 Requirements

• 1.3d Lower atmospheric thermal structure Measure
  temperature and pressure at the base of the
  atmosphere to accuracies of 1 K and 0.1
  microbar.
• Method Radio occultation
• Current Knowledge P 2000 nbar, T100 K _at_
  r1220 km (1988)
• P 5000 nbar, T100 K _at_ r1220 km (2002)
• Expectation Same
• Capability ?T 1 K REX (with Allan Deviation
  3E-13)
• ?P 100 nbar

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Level 1 Requirements

• 1.3e Evolution Determine the escape rate.
• Method Mass loading of solar wind by pickup
  ions (primary)
• Fit scale heights of various species from FUV
  solar occultation (secondary)
• Current Knowledge None
• Expectation 2E27 s-1 Krasnopolsky 1999
• 2E28 s-1 Tian Toon 2005
• Capability Unknown. Will likely require 3-D
  atmospheric model to simulate escape well
  enough. Interestingly, a possible
• constraint will be the detection of an
  atmosphere on Charon, as it will likely have
  accreted from Pluto.

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Level 2 Requirements

• 2.1 Characterize the time variability of Pluto's
  surface and atmosphere
• Method Look for changes on surface in visible
  imagery during flyby
• Look for evidence of volatile transport
  (e.g., near-terminator frosts, Triton-like
  geyers with wind streaks)
• Current Knowledge None
• Expectation Similar to Triton
• Capability OK, but flyby is short duration
  compared to seasonal timescale

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Level 2 Requirements

• 2.5 Characterize Pluto's ionosphere and solar
  wind interaction.
• Method Determine composition of pickup ions
  (primary)
• Radio occultation (secondary)
• EUV/FUV airglow (tertiary)
• Current Knowledge None
• Expectation Major ion HCNH, ionosphere peak at
  z1000 km, ne800 cm-3
• Capability negt1000 cm-3 (REX)
• Any ion FUV emissions will likely be due to
  ionization
• excitation of neutral atoms and/or
  dissociative ionization
• excitation of neutral molecules resonant
  scattering of sunlight from atomic ions is a
  minor source compared to other sources.

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Level 2 Requirements

• 2.6 Search for neutral species including H, H2,
  HCN, and CxHy, and other hydrocarbons and
  nitriles in Pluto's upper atmosphere, and obtain
  isotopic discrimination where possible.
• Method EUV/FUV solar occultation (primary)
• EUV/FUV airglow (secondary)
• Current Knowledge None
• Expectation f(H)4E-4, f(H2)5E-4, f(HCN)2E-4,
• f(C2H2)9E-4, f(C2H4)1E-4, f(C2H6)3E-5
• Capability f(H)gt1E-5, f(H2)gt2E-2, f(HCN)gt2E-4,
• f(C2H2)gt1E-5, f(C2H4)gt3E-6, f(C2H6)gt5E-4

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Level 2 Requirements

• 2.7 Search for an atmosphere around Charon
• Method EUV/FUV Solar occultation (primary), FUV
  Stellar occultation (secondary)
• Current Knowledge P(N2) lt 110,000
  pbar Sicardy et al. 2006
• P(CH4) lt 15,000 pbar Sicardy et al. 2006
• Expectation P(N2) 1400 pbar TSURF40K Pressure
  Balance
• P(N2) 0.4
  pbar TSURF100K with Pluto Outflow
• P(CH4) 0.3 pbar TSURF40K
• P(CH4) 0.004 pbar TSURF100K
• Capability P(N2) 7 pbar TSURF40K Solar
  Occultation
• P(N2) 11 pbar TSURF100K (t1 at limb)
• P(CH4) 11 pbar TSURF40K
• P(CH4) 17 pbar TSURF100K

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Nominal Charon Solar Occultation
Ingress Range 103,851 km Sun subtends 14.7 km
at Charon
Egress Range 106,669 km Sun subtends 15.1 km
at Charon
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Best Encounter Date

• For ATM, the factors affecting best encounter
  are
• The best solar occultation by Pluto but most of
  the encounters do well at meeting the main
  factors (solar diameter, fresnel scale,
  Sun-Earth-Pluto angle, and sky-plane velocity),
  which are slowly varying (best ranking was 7.2
  for encounter 11, worst was 6.7 for encounters 19
  21 the nominal encounter 14 had a ranking 7.1)
• A solar or stellar occultation by Charon only
  the nominal encounter 14 has a solar occultation
  (stellar occultations are somewhat random, and
  dont supply any flux at wavelengths lt91 nm,
  which are useful for detecting N2 and CO) the
  best ranking of 6.7 was thus for the nominal
  encounter, although very good stellar
  occultations exist for encounters 11, 15, and 20
  (at the nominal flyby distance)
• Bottom line the nominal encounter is the best
  date for ATM