M. Yamauchi 1, H. Lammer 2, J.-E. Wahlund 3 1. Swedish Institute of Space Physics (IRF), Kiruna, Sweden 2. Space Research Institute (IWF), Graz, Austria 3. Swedish Institute of Space Physics (IRF), Uppsala, Sweden O/H ratio of Atmospheric Escape from Non- magnetized Ancient Earth High EUV of early Sun means higher thermal loss of H but not O, predicting oxidation of the atmosphere. However, emergence of early life (prebiotic chemistry) requires reduced atmosphere. Can we solve this dilemma with non-thermal escape?

present Earthpresent Mars/Venuspresent Moon SW is stopped by the magnetic pressure (P B ) of the planetary B Ionopause P B is enhanced until it balances both SW P D (  sw v sw 2 ) and ionospheric plasma pressure P P (=  i kT i ) What type of interaction for ancient Earth? Conductivity of solid planet determines induction

(a) Most likely high EUV/FUV flux (b) Most likely high SW (solar wind) P D =  v sw 2 (c) Most likely strong & active IMF due to faster rotation (d) Most likely frequent & intense SEP (Solar Energetic Particle) Ancient solar forcing (Sun-in-Time) Ancient Magnetosphere/Ionosphere (e) Most likely less geomagnetic field than present (a) + (e)  Most likely P P >> P B at all height In such a case, the pressure-balance boundary between SW and ancient Earth is determined by the ionopause, and is not by the magnetopause, with "mini-magnetosphere" like Mars.  Non-magnetized for SW interaction & magnetized for ionospheric heating

processMechanismSpecieExplanationmain cause of increase Jeans escapethermal, neutral & ion H, HeThermal tail exceeds escape velocity Hot exosphere / hot ionosphere (high EUV) Hydrodynamic blow-off thermal, neutral & ion allThe same as Solar Wind and Polar Wind Hot exosphere / hot ionosphere (high EUV) Photochemical heating chemical, neutral H, HeRelease of energy of excited state molecule Hot exosphere / hot ionosphere (high EUV) Ion pickup & sub-sequent sputtering non-thermal, ion H, HeNewly ionized neutral inside SW takes cycloid motion Extended exosphere (high EUV) / thin ionosphere (high SW P D ) Energization by E // & EM wave non-thermal, ion allLocal deposit of SW energy to ionosphere generates EM field Active SW P D /IMF/SEP Large-scale momentum transfer non-thermal, ion allBulk plasma interaction at the boundary region. Active SW P D /IMF Various escape processes

Higher ionopause location means less neutrals (corona) beyond the ionopause.  Reduction of ion pick-up (of mainly H, He) Thick ionosphere also means more free electrons that impact on neutrals convert to ions. Such newly ionized neutrals inside the ionosphere are gyro-trapped by magnetized ionopause.  Reduction of Jeans escape (of mainly H, He) Observed non-thermal escape is as important as thermal escape. Observed non-thermal escape increases with F 10.7 flux. Terrestrial non-thermal escape increases with geomagnetic activity. Observed non-thermal escape increases during SEP event. Observed ionopause height increases with F 10.7 flux. We have to consider: Note: The ionopause = a magnetically shielding boundary whose magnetic pressure is balanced by the SW P D outside, and by the ionospheric plasma pressure inside, respectively, in a collision-free regime.

High ionopause during solar maximum for both Venus (Zhang et al., 2007) and Mars (Zhang et al., 1990). Frequent SEP (during solar maximum) probably caused high balance altitude by heating of the ionosphere. Ionopause vs. EUV/FUV (major) Ionopause vs. SW/IMF (minor) (d) strong (stable) IMF  no change as long as SW P D > SW P B (e) variable IMF  lower balance altitude (by cancellation of B) High SW P D decreases the altitude of pressure balance (Luhmann et al., 1980; Phillips et al., 1984).  The ancient condition is this extreme.

Qualitative Prognosis Increase inEUV/FUVSWDPIMF  (IMF) SEP Jeans & Photo- chemical (H, He) ++same + Hydrodynamic (all)++ (regime change) same + Ion pick-up (H, He)(#1)+same+ Wave and E // (all)++ (cf. Earth) + (cf. Earth) same+++ Momentum transfer (all) +++same++same O/H ratio of escape+ (#2)+same++ #1) depending on relative extent of ionosphere and exosphere #2) because non-thermal > thermal for Earth-sized planet

The ancient Earth can be considered as non-magnetized planet, whereas large part of the ionosphere is considered as magnetized (same as mini-magnetosphere of the Mars) where non-thermal heating is yet important. We expect much higher O escape & much higher O/H ratio of escape than present. The ancient atmosphere can be chemically quite reduced. Unclear parameters : atmospheric composition which is essential for both escape and O/H ratio of escape Conclusion To diagnose atmospheric evolution on early Earth and super-Earth, we qualitatively evaluate increases or decreases of non-thermal escape related to the ionosphere for nonmagnetized planets in response to changes in solar parameters. reference : Astrobiology J., 7(5), , 2007

[Kulikov et al.SpaceSciRev,2007; Tian et al. JGR, 2008] [Lichtenegger et al. Icarus in press, 2010] in agreement with Tian et al. JGR (2008) CO 2 -rich vs. N 2 -rich atmospheres