M. Yamauchi1, H. Lammer2, J.-E. Wahlund3 1. Swedish Institute of Space Physics (IRF), Kiruna, Sweden2. Space Research Institute (IWF), Graz, Austria3. 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 Earth present Mars/Venus present MoonSW is stopped by the magnetic pressure (PB) of the planetary B

Ionopause PB is enhanced until it balances both SW PD (swvsw

2) and ionospheric plasma pressure PP (= ikTi)

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) PD = vsw2

(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 PP >> PB at all heightIn 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

process Mechanism Specie Explanation main cause of increase

Jeans escape thermal,

neutral & ion

H, He Thermal tail exceeds escape velocity

Hot exosphere / hot ionosphere (high EUV)

Hydrodynamic blow-off

thermal,

neutral & ion

all The same as Solar Wind and Polar Wind

Hot exosphere / hot ionosphere (high EUV)

Photochemical heating

chemical,

neutral

H, He Release of energy of excited state molecule

Hot exosphere / hot ionosphere (high EUV)

Ion pickup & sub-sequent sputtering

non-thermal,

ion

H, He Newly ionized neutral inside SW takes cycloid motion

Extended exosphere (high EUV) / thin ionosphere (high SW PD)

Energization by E// & EM wave

non-thermal,

ion

all Local deposit of SW energy to ionosphere generates EM field

Active SW PD/IMF/SEP

Large-scale momentum transfer

non-thermal,

ion

all Bulk plasma interaction at the boundary region.

Active SW PD/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 F10.7 flux.

• Terrestrial non-thermal escape increases with geomagnetic activity.• Observed non-thermal escape increases during SEP event.

• Observed ionopause height increases with F10.7 flux.

We have to consider:

Note: The ionopause = a magnetically shielding boundary whose magnetic pressure is balanced by the SW PD 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 PD > SW PB

(e) variable IMF lower balance altitude (by cancellation of B)

• High SW PD decreases the altitude of pressure balance (Luhmann et al., 1980; Phillips et al., 1984).

The ancient condition is this extreme.

Qualitative PrognosisIncrease in EUV/FUV SWDP IMF (IMF) SEP

Jeans & Photo-chemical (H, He)

++ same same same +

Hydrodynamic (all) ++ (regime change)

same same same +

Ion pick-up (H, He) (#1) + same + 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

ConclusionTo 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), 783-800, 2007

50 40 30 20 10 0EUV/EUVPRESENT

100

1000

10000

TEXO

1 PALCO2

100 PAL,3.3%

96% CO2

↓ Hydrostatic regime

↑ Subsonic outflow

ε = 16%96% CO2

ε = 50%

[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)

CO2-rich vs. N2-rich atmospheres