Mars Aeronomy Science: Current Status, Future Plans, and Why it all Matters.

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Mars Aeronomy Science Current Status, Future
Plans, and Why it all Matters.

Stephen W. Bougher (University of
Michigan)
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Why Study the Mars Upper Atmosphere?
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MARS EXPLORATION PROGRAM ANALYSIS GROUP (MEPAG)
GOALS SUMMARY

• DETERMINE IF LIFE EVER AROSE ON MARS
• UNDERSTAND THE PROCESSES AND HISTORY OF CLIMATE
  ON MARS
• DETERMINE THE EVOLUTION OF THE SURFACE AND
  INTERIOR OF MARS
• IV. PREPARE FOR HUMAN EXPLORATION

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A. Objective Characterize Mars Atmosphere,
Present Climate, and Climate Processes

• ..a ground-to-exosphere approach to
  monitoring the atmospheric structure and dynamics
  is needed for a proper characterization of the
  present day climate of Mars.
• 1. Investigation Determine the processes
  controlling the present distributions of water,
  carbon dioxide, and dust by determining the short
  and long-term trends (daily, seasonal and solar
  cycle) in the present climate. Determine the
  present state of the upper (80 km) atmosphere
  (neutral/plasma) structure and dynamics quantify
  the processes that link the Mars lower and upper
  atmospheres.

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B. Objective Characterize Mars Ancient
Climate and Climate Processes

• .requires interdisciplinary study of
  the Martian surface and entire atmosphere.
• Investigation Determine the stable isotopic,
  noble gas, and trace gas composition of the
  present-day bulk atmosphere.
• Investigation Determine the rates of escape of
  key species from the Martian atmosphere, their
  correlation with seasonal and solar variability,
  their modification by remnant crustal magnetic
  fields, and their connection with lower
  atmosphere phenomenon (e.g. dust storms). From
  these observations, quantify the relative
  importance of processes that control the solar
  wind interaction with the Mars upper atmosphere
  in order to establish the magnitude of associated
  volatile escape rates. Extrapolate these
  processes into the past using models.

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Science and Engineering Objectives for Studying
Mars Upper Atmosphere

• Science Determine the rates of escape of key
  species from the Martian atmosphere.. Crucial
  constraints for atmospheric evolution models that
  extrapolate these rates to determine past
  climates (loss of water).
• Engineering Determine the short (diurnal and
  dust storm) and long term (seasonal and solar
  cycle) trends in the present upper atmosphere
  climate (80 km). Improve our engineering
  capability for aerobraking, aerocapture and EDL.
  Communications, etc.
• Requires global orbiter observations!

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Mars Upper Atmosphere Processes and Escape
Mechanisms Status of Estimated Escape Rates
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Martian Atmospheric Regions and Escape Processes
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Summary of Present Mars Volatile Escape
Mechanisms

• Thermal (Jeans) escape e.g. H
• Non-thermal escape
• Photochemical reactions DR of O2, N2, CO
  forming
• energetic (hot) atoms (e.g. O, N, C) with
  escape energies
• (2) Pick-up ion escape ions produced in the
  corona and exosphere are dragged along by SW
  B-field lines to partially escape (O, H, C).
• (3) Ionospheric outflows planetary ions are
  accelerated by the SW induced E-field and lost in
  the wake or crustal field cusps (e.g. O2).
• (4) Ion sputtering a portion of SW and
  pick-up ions can impact the neutral atmosphere
  with enough energy to eject neutral atmospheric
  particles at/above the exobase (e.g. CO2, N2, CO,
  O, N, C...).

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Influence of escape upon atmosphere and climate

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Upper Atmosphere Models Volatile Escape
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Requirements for Ancient Mars Climate Studies
Extrapolate Current Volatile Escape Processes
into Past

• Model for the early solar EUV fluxes (Ayres,
  1997 Rebas et al., 2005). (3 x Present EUV at
  2.5 GA)
• Model for the history of the solar wind
  properties
• (Newkirk, 1981 Wood et al., 2002).
• An assumed history of the planetary magnetic
  field Mars turn-off 3.7 GA (e.g. Acuna et al.,
  1998).
• Base models for ancient Mars conditions
  thermosphere neutral densities and temperatures
  (Bougher and Fox 1996 Bougher et al., 2004).

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Modern vs Ancient Mars Thermal Structure
(Bougher et al., 2004) MTGCM 2.5 GA (SZA
60)
Exobase Altitude 215 km (C) 250 km (A)
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Table of Various Estimates of Volatile Escape
Rates at Mars (e.g. O, O, O2)
Chassefiere and LeBlanc, 2004. Barabash, 2006
(Berlin) MEX-ASPERA
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Current Status Opportunity Science preceeding
a Dedicated Mars Aeronomy Mission
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Recent and Ongoing Orbital Measurements Relevant
to the Mars Upper Atmosphere

• MGS, Odyssey, and MRO aerobraking data
  (completed). Structure (densities, scale heights,
  temperatures, zonal winds)
• MGS Magnetometer/Electron Reflectometer (MAG/ER)
  measurements (ongoing). B-field maps, nightside
  neutral densities, electron spectra.
• MGS RS radio occultations (ongoing). Electron
  density profiles.
• Mars Express ASPERA-3 (neutral particle imaging
  detection, electron spectrometer, ion mass
  analyzer ongoing). Ionospheric outflows.
• Mars Express SPICAM (stellar occultations,
  airglow, aurora ongoing). Structure, wind
  tracer, seasonal airglow, intermittent aurora.
• Mars Express MARSIS (ongoing). Ionosphere
  sounding, electron density profiles, B-field
  strength.
• While these will provide valuable science and
  operations data, they do not, taken together,
  provide the understanding of the upper atmosphere
  structure, composition, dynamics, and variability
  necessary to address the pertinent science (e.g.
  volatile escape) questions.

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Exploring the Mars Neutral Upper Atmosphere With
Aerobraking Accelerometers
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MGS, Odyssey and MRO Latitudinal and Diurnal
Density Variations at 130km(Keating et al.,
2006)
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Dust Storm Impacts Density at 130 km(Bougher et
al., 1999)
MGS1 Orbit Number
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MGS1 Derived Zonal Winds (m/sec)Baird et al.
(2006)
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Solar Cycle and Seasonal Variation of Exospheric
Temperatures (Coupling On)
MAX
MOD
MGS2
MGS1
MRO (P026)
VL1
MIN
VL2
?T/?F10.7 0.8
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Mars Crustal Magnetic Fields MGS-MAG/ER (170
km B-nT)(Lillis et al., 2004 Mitchell et al.,
2006)
60
30
0
30
60
0E 90E
180E 270E
360E
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Nightside Electron Densities Enhanced by
Accelerated Incident Electrons at Cusps
(Fillingim et al., 2006)
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MGS-ER Derived Nightside (SLT 0200) 195 km
Neutral Densities (Lillis, 2006 Thesis)
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- Black observations - GCM predictions Blue
clear atmosphere Green nominal dust Red
dusty atmosphere
MEX SPICAM Atmospheric density (Forget et al.
2006)
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NASA Future Plans?
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Recent Calls for Mars Upper Atmosphere
Measurements Aeronomy Mission

• NRC COMPLEX Committees Assessment of Mars
  Science Mission Priorities COMPLEX, 2002
• ..there is an absence of NASA missions that
  specifically address Mars atmosphereionosphere
  and solar wind interactions
• Decadal Study Solar System Exploration Survey,
  2003
• ..The key dynamics of the upper atmosphere
  of Mars and rates of atmospheric escape should be
  studiedto constrain the rates of water loss from
  Mars, a key factor in the volatile history.
• Mars Exploration Program Analysis Group (MEPAG)
  2006
• Prioritized ranking of science goals and
  objectives gives high priority to
  upper-atmosphere studies as they pertain to
  climate evolution and control of planetary
  habitability. MEPAG Goals Document.
• MEPAG MSTO SAG Report (2006)
• Endorses MSTO science goals that address
  upper atmosphere characterization and volatile
  escape measurements at Mars.
• NRC Mars Architecture Assessment Committee
  (2006)
• Leave open Mars Scout science competitions
  (i.e. independent of core missions) to optimize
  science return provide balance to MEP.

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Recommendations to NASA HQMars Aeronomy
Exploration Workshop(August 2004)

• Upper atmosphere is an important part of the
  martian climate system (integrated from the
  interior to the exosphere). Recommend integrated
  approach.
• Important aspects of the upper-atmosphere can be
  observed from the unique perspective of a Telecom
  Orbiter (now MSTO) i.e. solar cycle
  observations.
• Although some notable observations of the upper
  atmosphere are being made at present, they are
  limited in scope and coverage .inadequate to
  address the major volatile escape processes and
  rates.
• Upper atmosphere plays important roles in
  programmatic aspects of the Mars exploration
  program i.e. engineering (EDL, aerobraking),
  radiation hazards to humans, communications.
• Necessary observations can be made from a
  dedicated spacecraft mission with appropriate
  orbit, lifetime, and instrumentation (Mars Scout
  mission profile).

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Measurement Objectives to Properly Address Mars
Volatile Escape Rates

• Characterize reservoirs available for escape
• Measure the neutral upper atmosphere
  (thermosphere, ionosphere, exosphere)
  composition, densities, and temperatures and
  their spatial and temporal (seasonal and solar
  cycle) variability. Systematic global
  measurements.
• Characterize thermal, dynamical, and wave related
  processes that couple the lower and upper
  atmospheres.
• Examine how the thermosphere chemically and
  dynamically couples with the ionosphere (e.g.
  ionization, ion-neutral chemistry).
• Measure parameters essential for determining
  volatile escape rates.
• Characterize (in terms of composition, energy,
  and spatial distributions) the escape fluxes of
  neutrals and ions (e.g. pickup ion fluxes).
• Examine how energy is transferred from the SW to
  the upper atmosphere ionosphere for various
  solar conditions. Establish connection between
  changing SW and solar radiation inputs and escape
  rates.
• Analyze the complex nature of the Mars B-field in
  solar wind interaction processes (impacting
  atmospheric stripping or erosion processes).

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Final Considerations for Mars Aeronomy

• The need to address volatile escape processes
  (determine rates) has not diminished with the
  discovery of past water on the surface of Mars
  (MER). Where did the water go?
• Dedicated Mars upper atmosphere mission is needed
  to quantify volatile escape rates in a
  comprehensive manner. Mars Scout mission envelop
  is likely sufficient.
• MSTO phased orbit scenario may be suited to
  monitoring long-term upper atmosphere and solar
  wind parameters key to addressing volatile escape
  and radiation hazards.
• Mars Scout 2011 or MSTO 2013 opportunities? At
  least four Mars Scout proposals were submitted
  that address Mars upper atmosphere and aeronomy
  questions.