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Solar Wind-Ionosphere Interaction at Mars/Venus and the Earth: Does a strong magnetic field protect a planetary atmosphere from stellar winds? H. Nilsson, M. Yamauchi, and S. Barabash Swedish Institute of Space Physics, Kiruna EANA-2012 (P4.28, 2012-10-15) Various escape processes process Jeans escape Hydrodynamic blow-off (Fig.3) Photochemical heating Ion pickup & subsequent sputtering (Fig. 5) Mechanism thermal, neutral semi-thermal, neutral & ion chemical, neutral non-thermal + thermal, ion non-thermal, ion Energization by E// & EM wave (Fig.3, 4) Large-scale non-thermal, momentum transfer ion 2 Specie Explanation H, He Thermal tail exceeds (& O) escape velocity main external cause Hot exosphere / hot ionosphere (high EUV) all The same as SW and Polar Wind Hot exosphere / hot ionosphere (high EUV) H, He (& O) Release of energy of excited state molecule Hot exosphere / hot ionosphere (high EUV) H, He (& O) Newly ionized neutral Extended exosphere inside SW takes cycloid (high EUV) / thin motion ionosphere (high SW PD) all Local deposit of SW Active SW PD/IMF/SEP energy to ionosphere generates EM field Bulk plasma interaction Active SW PD/IMF at the boundary region. all Escape of planetary atmosphere takes place mainly in two forms: as neutral atoms (thermal, photochemical and after charge exchange from ions) and as ions. Since the ion are trapped by the magnetic field, total loss in the form of ions might be strongly influenced by the presence of a planetary intrinsic magnetic field. 3 Observation Using similar ion instrument (IMA for Mars/Venus and CIS for the Earth), we derived atmospheric loss in the form of ions that exceed the escape velocity at Venus (10 km/s), Earth (11 km/s) and Mars (5km/s). note on observation: Strong spatial dependency (must consider spacecraft location) Limited angular coverage of the ion instrument of IMA (must integrate large set of data to make statistical distribution function) Figure 1: examples of obtained velocity distribution for Mars. By fitting these to shifted Maxwellian, we obtain distribution function and flux. 4 distribution Mars Venus Earth Figure 2: spatial distribution of total flux (most are escaping) 5 summary of escape Venus SW H+ precipitation SW He++ precipitation O+ escape at solar minimum O+ escape at solar maximum 1021~22/s 1020~21/s 3 x 1024/s 0.6~5 x 1025/s (Brace et al. 1987, McComas et al. 1986) Earth 1024/s 1023/s 1025/s 1025~26/s (Lennartsson et al. 2004) Mars 1021~22/s 1022/s 3 x 1024/s 3 x 1025/s (Lundin et al. 1989) We found that for current conditions the loss rate is similar for the three planets. The atmospheric escape may actually be stronger from a magnetized planet during increased solar wind activities. The intrinsic magnetic field does not protect the atmosphere from the solar wind for Earth’s case. note: May protect for strong magnetic field (Jupiter), but SW energy is high enough to make polar cap area large for the Earth. examples of acceleration Figure 3: outflowing ions above the Earth’s ionosphere (thick red lines: polar wind: fluctuation: wave acceleration) Figure 4: cold ions are accelerated as they travel tailward of the Mars. 6 Venus-Mars difference: gravity and size foreshock beam (reflected SW) pickup ion of exospheric SW reflection? origin SW SW BS Pickup ion is too weak to detect Figure 5: VEX and MEX frontside observations BS No foreshock at X>0 but SW reflection occurs 7 Future work: Geological scale? Ancient condition: (a) Most likely high EUV/FUV flux (b) Most likely high SW (solar wind) PD = vsw2 (c) Most likely strong & active Bsw (IMF) due to faster rotation (d) Most likely frequent & intense SEP (Solar Energetic Particle) (e) Most likely less planetary dynamo & more crust B-field (f) Different atmospheric composition (a)-(d) => must compare storm time observations to a statistical average - note: Different response times between magnetized and unmagnetized planets - note: Different atmospheric composition between planets - note: Different scale height between planets Example: Response to geoeffective solar flare (Futaana et al. 2008) Response to CIR at Earth and Mars (Wei et al. 2012) Statistical response to CIR, energy > 50 eV (Edberg et al. 2010) Statistical response to CIR, all ASPERA-3 energies (Nilsson et al. 2011) Some indications of stronger response at Mars (10 times more outflow) Statistical CIR response significantly smaller (~2.5 at Mars, 1.9 at Venus) Smaller or same total outflow (Smaller for solar minimum, same for solar maximum) At earth cold plasma is protons, what is the case for Mars and Venus? 8 Mars-Venus difference 11.5 11 10.5 10 9 9.5 8 -3 -2 -1 0 1 Mars-Sun axis [RM] 2 9 10