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Impact ­ Produced Exosphere of Europa

A.A. Berezhnoy Sternberg Astronomical Institute, Moscow, Russia


Equilibrium chemical composition of the impact-induced cloud
0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 3000 3500 4000 T, K 4500 OH H2 5000 O 5500 H H2O Q
0.0045 0.004 0.0035 0.003 0.0025 0.002 0.0015 0.001 0.0005 0 2000

Na

NaO H

NaO
3000

T, K

4000

5000

1.E-01 2000 Q 1.E-02 1.E-03 1.E-04

T, K 2500 CO 3000 3500 4000 4500 5000 CO
2

5500

HCO 1.E-05 1.E-06 CO O H


Elements Impact-

generated species

Species Species detected in the in cometary atmospheres vicinity of Europa

Species detected during SL9 ­ Jupiter collision (Shulman, 2002)
Na Not observed CO, CN, C2 (?), CO+ NH2 S2 Fe MgO

Na K C H S Fe Mg

Na, NaOH KOH, K CO, CO
2

Na K -

Na (near Sun) K (near Sun) CO, CO2, C2, CN H2O, OH SO2, H2S -

H2O, OH, H SO2, SO Fe

2

Mg, MgO, MgOH


0.1 0.08 0.06 0.04 0.02 0

PDF NaO H Photolys is NaO Photolys is

3500 K

5500 K V, m /s

0

1000

2000

3000

4000

5000

Probability density function of photolysis-generated Na atoms Upper limit of NaO and NaOH photolysis lifetimes on Europa are estimated to be 16 and 4 min, respectively. Dissociation rates of Na-containing molecules on Europa are determined by photolysis, not by electron impact.
Frac t ionat ion Fac t or 1. 04 1. 02 1 0. 98 0. 96 0. 94 0. 92 0. 9 0. 88 0. 86 2000 2500 3000 3500 4000 4500 5000 T, K 5500 6000 HD/ H2 D/ H HDO/ H2O OD/ OH

Deuterium exchange factor between the main H-bearing species versus the temperature of the cloud


Conclusions
Chemical composition of impact-produced clouds on Europa is estimated. Properties of photolysis-generated Na atoms are considered. Meteoroid bombardment leads to increasing of D/H ratio in water ice and destruction of complex organic compounds on Europa. Previous detection of cometary impacts on Europa is very tentative. Micrometeoroid source of Europa's exosphere can be studied by mass spectrometers on board future Europa landers.