Suprathermal C, N, and O atoms in the Martian upper atmosphere

Valery I. Shematovich

Institute of Astronomy, Russian Academy of Sciences

Suprathermal heavy atoms at Mars

In collaboration with:

H. Lammer, H. Groeller, H. Lichtenegger (Space Research Institute AAS, Graz, Austria);M.N. Krestyanikova, M. Ya. Marov (Institute of Applied Mathematics RAN, Moscow )D.V. Bisikalo (Institute of Astronomy RAN, Moscow )

Hot or suprathermal atomsSuprathermal atoms are formally defined as atoms with kinetic

energies E > 5 –10 kT – mean thermal energy of surrounding gas

Thermal processes

Hot or suprathermal atomsSuprathermal atoms are formally defined as atoms with kinetic

energies E > 5 –10 kT – mean thermal energy of surrounding gas

Nonthermal processes induced by the energy Deposition.

Suprathermals play animportant role in:- atmospheric chemistry;-- UV emissions;-- atmospheric loss.

Hot or suprathermal atoms Suprathermal atoms (with kinetic energies E > 5 –10 kT) are produced in the various nonthermal processes: • Photochemical sources: dissociative recombination of

molecular ions; photon and electron impact dissociation; exothermic chemical reactions

•

• Plasma sources: charge exchange with and atmospheric sputtering by high-energy magnetospheric and/or solar wind ions

•

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Hot atom kinetics:

Suprathermal atoms loose their translational energy in elastic and inelastic collisions with the ambient atmospheric gas

When suprathermal atoms chemically differ from the ambient gas these relaxation collisions lead to thermalization of the primary suprathermal particles. Usually this process is considered in the linear approximation.

In the case when A = B, the subsequent collisions with the ambient gas lead to cascade formation of new hot atoms because atoms of secondary origin may be produced with the suprathermal energies (E ’’ >> kT) .

)()()( EEBEEABEA hothotthhot

Kinetic Boltzmann equation:

together with initial and boundary conditions for the atmospheric region G( r) with a boundary surface (G). This system of kinetic equations for suprathermal heavy atoms is solved using the Direct Simulation Monte Carlo (DSMC) method.

Distribution of suprathermal atoms in the atmospheric rarefied gas is evaluated through the solution of Boltzmann-type kinetic equations with the source terms

Suprathermal heavy atoms at Mars

(from Lundin et al., 2004)

•McElroy, Science, 1972. •Nagy and Cravens, GRL, 1998.•Ip, Icarus, 1988, GRL, 1990. - 1D MC•Lammer and Bauer, J. Geophys. Res., 1991. - 1D MC•Kim et al., J. Geophys. Res., 1998.•Hodges, J. Geophys. Res., 2000, GRL, 2002. - MC•Krestyanikova, and Shematovich, Solar System Res., 2005, 2006. – 1D DSMC•Cipriani et al., J. Geophys. Res., 2006. - 3D MC•Chaufray et al., J. Geophys. Res., 2007. - 3D MC•Johnson et al., Sp. Sci. Rev., 2008•Valeille et al., Icarus, 2009; JGR, 2009, 2010. - 3D DSMC•Fox and Hac, JGR, 1997; Icarus, 2009, 2010. – 1D MC•Groeller et al., J. Geophys. Res., 2010 (subm.) -3D MC

Suprathermal oxygen at Mars

Dissociative recombination of the molecular ions:

XY+(v) + e X(x1,x2,…) + Y(y1,y2,…) + ΔE

v – vibrational excitation of the ion electronic ground state;

xi, yj – electronic excitation states of the ion fragments;

ΔE – excess kinetic energy for ion fragments

ΔE=EDXY + EXY+(v) - EX(xi) - EY(yj)

It is important to know the total and partial cross sections for DR

in dependance on collision energy.

Heavy suprathermals at Mars: sources

O2+ + e O(3P) + O(3P) + 6.96 eV 0.265 0.073 0.02 0.22 0.25

O2+ + e O(3P) + O(1D) + 5.00 eV 0.473 0.278 0.764 0.42 0.39

O2+ + e O(1D) + O(1D) + 3.02 eV 0.204 0.510 0.025 0.31 0.27

O2+ + e O(1D) + O(1S) + 0.80 eV 0.058 0.139 0.211 0.05 0.09

Branching ratios for Ecoll = 0

[Petrignani et al., 2005] [Kella et al., 1997]

v = 0 v = 1 v = 2 v = 0 v > 0

0.22, 0.42, 0.31, and 0.05 for v = 00.28, 0.36, 0.23, and 0.13 for v > 0

Used branching ratios:

[Fox and Hac, 2009]

Hot oxygen at Mars: sources

Dissociative recombination of O2+ ion

Cross section and branching ratios versus collision energy (Peverall et al., J. Chem. Phys., 2001).

13

Energy distribution of hot O atoms formed in O2+ DR

120 km altitude

200 km altitude

14

Kinetics of the suprathermal O atoms

• Elastic collision:

• Quenching collision:

Release of energy: 1.97 eV for the 1D state and

4.19 eV for the 1S state

• Inelastic collision:

15

Total and differential cross sections:

[Balakrishnan et al., 1998]

[Kharchenko et al., 2000]

Differential cross sections for elastic collisions of O(3P) +

O(3P)Elastic cross sections for O(3P) + O(3P) collisions

[Kharchenko et al., 2000]

Elastic cross sections for O(3P) + N2 collisions

We use the O + O cross sections for O collisions with neutral background atoms.

Hot oxygen at Mars: Energy Distribution Functions (EDFs) for low solar activity - MEX conditions

[Krestyanikova and Shematovich, Sol. Syst. Res. 40, 384, 2006]

[Ip, Icarus 76, 135, 1988][Kim et al. JGR 103, 29339,1998]

Hot O atoms

Cold O atoms

~(2.9÷4.5) × 1025 s-1

Hot oxygen at Mars: Energy Distribution Functions(EDFs)Calculated EDF – solid lines;Thermal EDF – dashed lines;Left vertical line – shows the region of suprathermal energies;Right vertical line – shows the escape energy.It is seen that:-suprathermal tail is formed

including the escaping flux ~ (4.1 –5.6)×107 cm-2 s-1;- hot atoms with energies between vertical lines populate the hot corona. LOW SOLAR ACTIVITY

Hot oxygen at Mars: hot corona

Thermal hot fraction atexospheric temperatureT=180 K (solar min.)

Nonthermal hot fractionfrom O2

+ dissociativerecombination and atmospheric sputtering.

Comparison with:•Nagy & Cravens 1988;•Lammer & Bauer 1991.

LOW SOLAR ACTIVITY

Different height scales!

UV emissions in the upper atmosphere of Mars – comparison with SPICAM MEX observations (Chaufray et al., JGR, 2008)

Brightness of OI 130.4 nm triplet in dependence on exospheric temperature. Possible input of hot oxygen corona?

ASPERA-3 measurements of ENAs?

Hot carbon at Mars: sources

•Fox and Hac, JGR, 1999.•Nagy et al., J. Geophys. Res., 2001.•Chaufray et al., J. Geophys. Res., 2007.•Johnson et al., Sp. Sci. Rev., 2008

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Hot nitrogen at Mars: sources

•Fox and Dalgarno, JGR, 1983.•Fox and Hac, J. Geophys. Res., 1997.•Johnson et al., Sp. Sci. Rev., 2008

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23EDF at 240 km altitude for low solar activity:

Suprathermal heavy atoms at Mars

Density profiles for high and low solar activity

Suprathermal heavy atoms at Mars

Escape fluxes and Loss rates for oxygen:

Escape process Loss rate [s-1]

Ion pick up of O+ 2 x 1024 (MEX, Science, 2007)

Sputtering of O 3.5 x 1023 (Leblanc&Johnson, 2002)

Cool ion outflow ≤ 1025

Ion escape of CO2+, O2

+ ≤ 1024 (Lundin et al., 2008)

Timeline of atmospheric loss at Mars

Hot corona at Mars

At present time the atmospheric escape at Mars is dominated by loss of suprathermal neutrals – H, C, N, and O.

Suprathermal heavy atoms in the Martian corona play an important role in the Mars’ interaction with the solar wind.

Models are still strongly limited by a poor availability of the data on differential cross sections for the Oh, Ch – CO2, N2, O2, O collisions at energies below a few keVs. Hopefully, they will be tested and improved when the new data on the upper atmosphere of Mars will be available (MEX, PhSRM, MAVEN,…). Thank you for the attention!

Suprathermal heavy atoms at Mars: Conclusions