Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of...
-
date post
21-Dec-2015 -
Category
Documents
-
view
214 -
download
1
Transcript of Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of...
![Page 1: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/1.jpg)
Crustal Fields in the Solar Wind:
Implications forAtmospheric Escape
Dave Brain
LASP
University of Colorado
July 24, 2003
![Page 2: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/2.jpg)
Atmospheric Escape to Space
• Evidenceisotope measurementsspacecraft (Phobos, MGS)ionosphere models
• Why do we care?Climate historyAtmospheric chemistry
• Loss estimates.15 - 1 bar CO2 (over history) 1025 - 1026 particles / s ( today )
![Page 3: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/3.jpg)
Atmospheric Escape to Space
• Main issues
#1 Loss over Martian historyAmountTiming
#2 Today’s lossAmountSpecies
Processes
To improve estimates of #1, must improve knowledge in many areas, including #2
![Page 4: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/4.jpg)
MGS Measurements
• Ancient dynamo( early protection for atmosphere )
• Strong crustal sources( affect loss after dynamo turn-off )
this was an animation
![Page 5: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/5.jpg)
Loss Today
![Page 6: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/6.jpg)
Relevant Loss Processes
• Photochemical loss
• Ion pickup • Sputtering
• Bulk removal
neutralion
(Contemporary)
![Page 7: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/7.jpg)
Relevant Loss Processes
• Photochemical loss
• Ion pickup • Sputtering
• Bulk removal
Crustal sources affect these processes through:atmospheric shieldingfield topologyopen field lines
neutralion
(Contemporary)
![Page 8: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/8.jpg)
Atmospheric Shielding
![Page 9: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/9.jpg)
Atmospheric Shielding
Implications of shielding:
1. Reduced ionization charge exchange electron impact
2. Photo-ion motion changed
![Page 10: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/10.jpg)
Atmospheric Shielding
LS = 0 SW Pressure = 5e-9 dynes cm-2
Theoretical Martianpressure balance obstacle
to the solar wind
PSW = Pcrust + Pionosphere
this was an animation
![Page 11: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/11.jpg)
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?
CO2: < 10% O: 10-60 %
![Page 12: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/12.jpg)
Field Topology
![Page 13: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/13.jpg)
Field Topology
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
![Page 14: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/14.jpg)
Field Topology
With crustal sources Without crustal sources
Crustal sources severely alter the field topology close to Mars
MHD simulations(courtesy Y. Ma and A. Nagy)
![Page 15: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/15.jpg)
Field Topology
these were animations
![Page 16: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/16.jpg)
Open Field Lines
![Page 17: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/17.jpg)
Open Field Lines
Implications of open field lines:
1. Access to lower atmosphere for SW charged
particles
2. “Escape hatches” for planetary ions
![Page 18: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/18.jpg)
Open Field Lines
Open field lines exist near crustal “cusps” of near-vertical field
Dayside Data
![Page 19: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/19.jpg)
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
![Page 20: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/20.jpg)
Loss over Martian History
![Page 21: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/21.jpg)
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
Time
![Page 22: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/22.jpg)
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
![Page 23: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/23.jpg)
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
![Page 24: Crustal Fields in the Solar Wind: Implications for Atmospheric Escape Dave Brain LASP University of Colorado July 24, 2003.](https://reader035.fdocuments.us/reader035/viewer/2022081519/56649d585503460f94a37655/html5/thumbnails/24.jpg)
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