1. Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003

2. Atmospheric Escape to Space Evidence isotope measurements spacecraft (Phobos, MGS) ionosphere models Why do we care? Climate history Atmospheric chemistry Loss estimates.15 - 1 bar CO 2 (over history) 10 25 - 10 26 particles / s( today )

3. Atmospheric Escape to Space Main issues #1 Loss over Martian history Amount Timing #2 Today’s loss Amount Species Processes  To improve estimates of #1, must improve knowledge in many areas, including #2

4. MGS Measurements Ancient dynamo ( early protection for atmosphere ) Strong crustal sources ( affect loss after dynamo turn-off ) this was an animation

5. Loss Today

6. Relevant Loss Processes Photochemical loss Ion pickup Sputtering Bulk removal neutral ion (Contemporary)

7. Relevant Loss Processes Photochemical loss Ion pickup Sputtering Bulk removal  Crustal sources affect these processes through: atmospheric shielding field topology open field lines neutral ion (Contemporary)

8. Atmospheric Shielding

9.         Implications of shielding: 1. Reduced ionization charge exchange electron impact 2. Photo-ion motion changed

10. Atmospheric Shielding L S = 0 SW Pressure = 5e-9 dynes cm -2 Theoretical Martian pressure balance obstacle to the solar wind P SW = P crust + P ionosphere this was an animation

11. Atmospheric Shielding With crustal sources Without crustal sources The volume of protected atmosphere is larger (by a factor of 2-8) when crustal sources are considered. How many (more) neutrals are protected? CO 2 : < 10% O: 10-60 %

12. Field Topology

13. Implication of altered topology: Modification of charged particle motion Escape could be enhanced or diminished depending upon orientation of crustal fields relative to solar wind flow

14. Field Topology With crustal sourcesWithout crustal sources  Crustal sources severely alter the field topology close to Mars MHD simulations (courtesy Y. Ma and A. Nagy)

15. Field Topology these were animations

16. Open Field Lines

17. Implications of open field lines: 1. Access to lower atmosphere for SW charged particles 2. “Escape hatches” for planetary ions

18. Open Field Lines  Open field lines exist near crustal “cusps” of near-vertical field Dayside Data

19. Open Field Lines Estimates of quantity of open field lines Simple models ~7% by area at exobase (~200 km) in region of strong crustal sources MAG Data ~ 1-2% by area on Martian dayside (2pm local time) at 400 km

20. Loss over Martian History

21. Magnetic History Mars forms Dynamo on Surface strongly magnetized Dynamo off Large impacts - magnetization erased Northern resurfacing - magnetization erased Relaxation of crustal magnetization to present Time

22. Loss over Martian History Magnetic History Mars forms Dynamo on Surface strongly magnetized Dynamo off Large impacts - magnetization erased Northern resurfacing - magnetization erased Relaxation of crustal magnetization to present Impact ~3.5 Gya Shielding from global field Shielding by crustal sources Outgassing

23. Needed Measurements Concurrent particle and field measurements! Low-altitude (and surface) measurements of crustal magnetization Atmospheric/ionospheric density and temperature at high altitude Measurements of carrier and grain size of magnetization Solar wind measurements at Mars Time history of ionization processes at Mars Coverage in local time, SZA, altitude, and geographic location

24. Summary Atmospheric escape to space has important implications for Mars’ past climate and current atmospheric chemistry Crustal magnetic sources might effect present loss rates: shielding of the atmosphere alteration of particle trajectories through field topology particle exchange along open field lines Crustal effects have persisted since Mars’ dynamo ceased