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The EUV impact on ionosphere: What do observations indicate for atmospheric evolution of early Earth and Exo-Earths? J.-E. Wahlund and M. Yamauchi Swedish Institute of Space Physics (IRF) ON3 Response of atmospheres and magnetospheres of terrestrial planets to extreme solar/stellar conditions Various escape processes process Jeans escape Mechanism Explanation thermal, Thermal tail exceeds escape light neutral/ion velocity Hydrodynamic blow-off thermal, Extreme EUV condition at neutral/ion early Sun/Star. Photochemical heating chemical, light Release of energy in the neutral excited atomic state. non-thermal, Ion pickup & subNewly exposed ions to SW is light ion sequent sputtering subject to SW DC field. non-thermal, Non-thermal ion Local deposit of SW energy to energization by E// & EM light/heavy ion ionosphere causes EM field wave that energizes ions. non-thermal, Large-scale SWDP & EM forces push bulk light/heavy ion plasma anti-sunward at the momentum transfer boundary region. Today's keyword : Ionosphere 1. As source of non-thermally escaping ions. 2. As protector to keep "neutrals to be escape" inside ionosphere (Jeans escape + ion pick-up). 3. As a modifier of large-scale momentum transfer. (a) The evolution of the planetary atmosphere might be dependent on the ionospheric condition and its activity. (b) Consider dependence of escape on solar EUV/FUV & solar wind (SW). hints for extreme conditions at early Sun/star EUV & SW dependence of ionospheric contribution: 1. as source As: Source of Protect from Magnetized Unmagnetized waverelated heating (Jeans) Amplify O+-related by instability ? Key word localized energy deposit to ionosphere (Jeans) relative height of ionopause & ion pick-up exosphere (interaction bulk momentum area increase) transfer Fact 1: high rate of non-thermal ion escape Escape at solar maximum Mars: 0.5 kg/s (O+, O2+) Venus: 2kg/s (O+) Earth: 1 kg/s (O+) Cluster/CIS H+ O+ Lundin et al., 2004 (Nilsson et al., 2004) Fact 2a: Ion escape increases with F10.7 flux Between solar max & min (factor 3 difference in F10.7 flux): Earth: a factor of 102 (or 3) change for O+ (or H+) outflow. largest contribution & high O/H ratio at early Earth ? (Cully et al., 2003) Venus: a factor of 20 change in ionotail density. Mars: a factor of 102 difference between MEX and Phobos-2 (but need revision). Fact 2b: Non-thermal ion escape increases with geomagnetic activity Akebono/DE/Polar Freja@h=1700km (Norqvist et al., 1998) (Cully et al., 2003) H+ O+ (Broad-Band Electrostatic Low Frequency wave) (Lower Hybrid or Electro-Magnetic Ion Cyclotron wave) (1) in various forms (2) depend strongly on Kp, SWDP, and IMF EUV & SW dependence of ionospheric contribution: 2. as protector As: Source of Protect from Magnetized Unmagnetized waverelated heating (Jeans) Amplify O+-related by instability ? Key word localized energy deposit to ionosphere (Jeans) relative height of ionopause & ion pick-up exosphere (interaction bulk momentum area increase) transfer SW wind interaction with atmosphere present/ancient Earth? present Mars/Venus? ancient Mars/Venus? ancient Earth? SW is stopped by the magnetic pressure of the dipole field Interplanetary magnetic field (IMF) is enhanced around the ionosphere due to induction current For reference Protection by ionosphere In both magnetized/unmagnetized planets, strong Bfield lies between the ionosphere and (shocked) SW. 1. Thick ionosphere means higher ionization rate by the electron impact ionization. Extra ionization of neutrals with escape velocity, while these ions cannot escape beyond the magnetized ionopause/magnetopause. Reduction of Jeans escape (of mainly H, He) 2. Higher ionopause location means less neutrals (corona) beyond the ionopause. Reduction of ion pick-up (of mainly H, He) Fact 3: Ionopause is EUV/FUV dependent Solar cycle variation of the ionopause height: Venus : 1700 km difference between solar maximum (high) and solar minimum (low) (Zhang et al., 2007). The same tendency for Mars (Zhang et al., 1990). Therma/non-thermal ratio = out-of-phase of solar cycle cf. SW dependence of ionopause height We expect: (a) strong (stable) IMF no change (b) variable IMF lower balance altitude (by cancellation of B) (c) strong SWDP lower balance altitude Therma/non-thermal ratio = out-of-phase of SW activity Fact 4a: extra ionization (cold case) high ionization (by electron impact) & subsequent escape are observed at Titan (Wahlund et al., 2005) Fact 4b: extra ionization (hot case) Critical ionization velocity (CIV) Possible extra ionization by, e.g., critical ionization velocity mechanism EUV & SW dependence of ionospheric contribution As: Source of Protect from Magnetized Unmagnetized waverelated heating (Jeans) Amplify O+-related by instability ? Key word localized energy deposit to ionosphere (Jeans) relative height of ionopause & ion pick-up exosphere (interaction bulk momentum area increase) transfer Magnetized planet increase in EUV/FUV SWDP (IMF) + + Non-thermal heating +++ Jeans + photochemical Ion pick-up ++ same same same same same same same Large-scale momentum transfer O/H ratio ++ IMF + (?) + + (?) + (?) (#1) ++ + + (#1) Increase or decrease depending on the relative importance of non-thermal heating Unmagnetized planet increase in EUV/FUV SWDP Non-thermal heating Jeans + photochemical Ion pick-up Large-scale momentum transfer O/H ratio ++ (?) ++ + (?) IMF (IMF) same + same same same (#2) ++ same + ++ + same ++ (#1) ++ same + #1) depending on relative importance of non-thermal heating. #2) depending on relative extent of ionosphere and exosphere Since ancient Earth's ionosphere is * Most likely High EUV/FUV * More likely High SWDP * Probably strong/active IMF much higher O escape & much higher O/H ratio of escape than present. The ancient atmosphere can be chemically quite reduced Unclear parameters : Magnetized or non-magnetized, atmospheric composition, internal condition End Extra slides for Q & A Budget above the Earth's ionosphereH+/O+ in major return route ion escape < 10 eV (2~3 Re) > 10 eV (3~4 Re) H+ 2~5 2~8 O+ 1~3 1.5~20 ion precipitation ion electron > 10 eV (DMSP) 0.2~0.9 9~60 in 1025 /s mass budget out in in kg/s H+ O+ meteors 0.05~0.2 < 0.02 0.5~5 ? 0.5 After Moore et al., 1999 Magnetized planet (Earth, Mercury) Magnetopause : balance between SW PD Planetary magnetic field (a) stronger but stable IMF lower altitude of magnetopause but more return flow (b) more variable IMF more internal process (non-thermal escape) (c) stronger SW PD lower altitude of magnetopause + escape How about UV dependence ? (important for ancient condition) Height and density of the ionosphere (1) Ionization (source) = Chapman model One-component atmosphere (scale height = H 1/gravity) s: cross section, F0:incoming solar flux, n0:density at z=0 Peak altitude : zmax(c , F0, H) = H ln(n0sH/cos(c)) does not depends on F0 , but on H (i.e., gravity) Peak production : qmax (c , F0 , H) = F0cos(c)/H exp(1) depends on F0 and H (i.e., gravity) (2) Transport (recombination loss is ignorable) Moves peak of ne(z) much higher with less sharp ne(z) profile Transport (convection) is mainly driven by heating ( q) Ionospheric extent depends on both F0 and gravity Escape from the cusp Earth ? Mars ? Venus ? Io & other Satellites?