1. The EUV impact on ionosphere: 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 What do observations indicate for atmospheric evolution of early Earth and Exo-Earths?

2. Various escape processes processMechanismExplanation Jeans escape thermal, light neutral/ion Thermal tail exceeds escape velocity Hydrodynamic blow-off thermal, neutral/ion Extreme EUV condition at early Sun/Star. Photochemical heating chemical, light neutral Release of energy in the excited atomic state. Ion pickup & sub- sequent sputtering non-thermal, light ion Newly exposed ions to SW is subject to SW DC field. Non-thermal ion energization by E // & EM wave non-thermal, light/heavy ion Local deposit of SW energy to ionosphere causes EM field that energizes ions. Large-scale momentum transfer non-thermal, light/heavy ion SWDP & EM forces push bulk plasma anti-sunward at the boundary region.

3. 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

4. EUV & SW dependence of ionospheric contribution: 1. as source As:MagnetizedUnmagnetizedKey word Source of wave- related heating ?localized energy deposit to ionosphere Protect from (Jeans) ion pick-up relative height of ionopause & exosphere Amplify by O+-related instability (interaction area increase) bulk momentum transfer

5. Fact 1: high rate of non-thermal ion escape Lundin et al., 2004 (Nilsson et al., 2004) H+H+ O+O+ Cluster/CIS Escape at solar maximum Mars: 0.5 kg/s (O +, O 2 + ) Venus: 2kg/s (O + ) Earth: 1 kg/s (O + )

6. Fact 2a: Ion escape increases with F 10.7 flux Venus: a factor of 20 change in ionotail density. Mars: a factor of 10 2 difference between MEX and Phobos-2 (but need revision). (Cully et al., 2003) Between solar max & min (factor 3 difference in F 10.7 flux): Earth: a factor of 10 2 (or 3) change for O + (or H + ) outflow.  largest contribution & high O/H ratio at early Earth ?

7. Fact 2b: Non-thermal ion escape increases with geomagnetic activity (Broad-Band Electrostatic Low Frequency wave) (Lower Hybrid or Electro-Magnetic Ion Cyclotron wave) (2) depend strongly on Kp, SWDP, and IMF Freja@h=1700km (Norqvist et al., 1998) Akebono/DE/Polar (Cully et al., 2003) (1) in various forms O+O+ H+H+

8. EUV & SW dependence of ionospheric contribution: 2. as protector As:MagnetizedUnmagnetizedKey word Source of wave- related heating ?localized energy deposit to ionosphere Protect from (Jeans) ion pick-up relative height of ionopause & exosphere Amplify by O+-related instability (interaction area increase) bulk momentum transfer

9. SW wind interaction with atmosphere present/ancient Earth? ancient Mars/Venus? present Mars/Venus? ancient Earth? For reference SW is stopped by the magnetic pressure of the dipole field Interplanetary magnetic field (IMF) is enhanced around the ionosphere due to induction current

10. Protection by ionosphere In both magnetized/unmagnetized planets, strong B- field 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)

11. 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

12. 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

13. Fact 4a: extra ionization (cold case) high ionization (by electron impact) & subsequent escape are observed at Titan (Wahlund et al., 2005)

14. Fact 4b: extra ionization (hot case) Possible extra ionization by, e.g., critical ionization velocity mechanism Critical ionization velocity (CIV)

15. EUV & SW dependence of ionospheric contribution As:MagnetizedUnmagnetizedKey word Source of wave- related heating ?localized energy deposit to ionosphere Protect from (Jeans) ion pick-up relative height of ionopause & exosphere Amplify by O+-related instability (interaction area increase) bulk momentum transfer

16. Magnetized planet increase inEUV/FUVSWDPIMF  (IMF) Non-thermal heating+++++++ Jeans + photo- chemical ++same Ion pick-upsame Large-scale momentum transfer + (?)+ O/H ratio(#1)++++ (#1) Increase or decrease depending on the relative importance of non-thermal heating

17. Unmagnetized planet increase inEUV/FUVSWDPIMF  (IMF) Non-thermal heating++ (?)+ (?)same+ Jeans + photo- chemical ++same Ion pick-up (#2) ++same+ Large-scale momentum transfer +++same++ O/H ratio(#1)++ same + #1) depending on relative importance of non-thermal heating. #2) depending on relative extent of ionosphere and exosphere

18. 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

19. End

20. Extra slides for Q & A

21. Budget above the Earth's ionosphereH+/O+ in major return route ion escape H+H+ O+O+ < 10 eV (2~3 Re) 2~51~3 > 10 eV (3~4 Re) 2~81.5~20 ion precipitationionelectron > 10 eV (DMSP)0.2~0.99~60 in 10 25 /s mass budgetH+H+ O+O+ meteors out0.05~0.20.5~5- in< 0.02?0.5 in kg/s After Moore et al., 1999

22. Magnetized planet (Earth, Mercury) Magnetopause : balance between SW P D  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 P D  lower altitude of magnetopause + escape How about UV dependence ? (important for ancient condition)

23. Height and density of the ionosphere (1) Ionization (source) = Chapman model One-component atmosphere (scale height = H  1/gravity)  : cross section, F 0 :incoming solar flux, n 0 :density at z=0 Peak altitude : z max ( , F 0, H) = H ln(n 0  H/cos(  ))  does not depends on F 0, but on H (i.e., gravity) Peak production : q max ( , F 0, H) = F 0 cos(  )/H exp(1)  depends on F 0 and H (i.e., gravity) (2) Transport (recombination loss is ignorable) Moves peak of n e (z) much higher with less sharp n e (z) profile Transport (convection) is mainly driven by heating (  q)  Ionospheric extent depends on both F 0 and gravity

24. Escape from the cusp Earth ? Mars ? Venus ? Io & other Satellites?