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

1. Mars Aeronomy Science: Current Status, Future Plans, and Why it all Matters. Stephen W. Bougher (University of Michigan)

2. Why Study the Mars Upper Atmosphere?

3. 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

4. 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 determiningthe 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.

5. 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.

6. 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!

7. Mars Upper Atmosphere Processes and Escape Mechanisms: Status of Estimated Escape Rates

8. Martian Atmospheric Regions and Escape Processes

9. Summary of Present Mars Volatile Escape Mechanisms • Thermal (Jean’s) 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...).

10. Influence of escape upon atmosphere and climate

11. Upper Atmosphere Models : Volatile Escape

12. 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).

13. Modern vs Ancient Mars Thermal Structure (Bougher et al., 2004) MTGCM 2.5 GA (SZA ~ 60) Exobase Altitude : ~215 km (C) ~250 km (A)

14. Table of Various Estimates of Volatile Escape Rates at Mars (e.g. O, O+, O2+) Chassefiere and LeBlanc, 2004. **Barabash, 2006 (Berlin) MEX-ASPERA

15. Current Status: “Opportunity Science” preceeding a Dedicated Mars Aeronomy Mission

16. 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.

17. Exploring the Mars Neutral Upper Atmosphere With Aerobraking Accelerometers

18. MGS, Odyssey and MRO Latitudinal and Diurnal Density Variations at 130km(Keating et al., 2006)

19. Dust Storm Impacts: Density at 130 km(Bougher et al., 1999) MGS1 Orbit Number

20. MGS1 Derived Zonal Winds (m/sec):Baird et al. (2006)

21. Solar Cycle and Seasonal Variation of Exospheric Temperatures (Coupling On) MAX MOD *MGS2 *MGS1 *MRO (P026) *VL1 MIN *VL2 ΔT/ΔF10.7 ~ 0.8

22. 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

23. Nightside Electron Densities Enhanced by Accelerated Incident Electrons at Cusps (Fillingim et al., 2006)

24. MGS-ER Derived Nightside (SLT = 0200) 195 km Neutral Densities (Lillis, 2006 Thesis)

25. - Black : observations - GCM predictions : Blue : clear atmosphere Green : nominal dust Red : dusty atmosphere MEX SPICAM Atmospheric density (Forget et al. 2006)

26. NASA Future Plans?

27. Recent Calls for Mars Upper Atmosphere Measurements & Aeronomy Mission • NRC COMPLEX Committee’s Assessment of Mars Science Mission Priorities [COMPLEX, 2002] : “..there is an absence of NASA missions that specifically address Mars atmosphere…ionosphere 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 studied…to 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.

28. Recommendations to NASA HQ:Mars 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).

29. 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).

30. 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.