The EUV impact on ionosphere:

1. 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

2. Various escape processes

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

5. 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)

6. 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).

7. Fact 2b: Non-thermal ion escape increases with geomagnetic activity Akebono/DE/Polar (Cully et al., 2003) Freja@h=1700km(Norqvist et al., 1998) 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

8. EUV & SW dependence of ionospheric contribution: 2. as protector

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) Critical ionization velocity (CIV) Possible extra ionization by, e.g., critical ionization velocity mechanism

15. EUV & SW dependence of ionospheric contribution

16. Magnetized planet (#1) Increase or decrease depending on the relative importance of non-thermal heating

17. Unmagnetized planet #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 in 1025 /s in kg/s After Moore et al., 1999

22. 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)

23. 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

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