The electrochemical process generated by simulation experiments of Venusian lightning

The electrochemical process generated by simulation experiments of Venusian lightning

Hongkun Qu^1,3, Alian Wang¹, and and Elijah Thimsen²

¹Dept. of Earth and Planetary Sciences and the McDonnell Center for the Space Sciences, ²McKelvey School of Engineering, Washington University in St. Louis, One Brookings Drive, St. Louis, MO, 63130, USA. One Brookings Drive, St. Louis, MO, 63130, USA. ³Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Institute of Space Sciences, Shandong University, Weihai, Shandong,264209, China. (hongkun.qu@wustl.edu )

 

Introduction

Lightning (one type of electrostatic discharge), as an important electrical process for planets with atmosphere, which has been detected on many planets in our solar system, e.g., Earth, Jupiter [1], Saturn [2], Uranus [3], and Neptune [3], and might occur on Mars [4], Venus [5], and Tian [6]. The earliest observation of Venus lightning was reported by Ksanfomaliti … mission name [7]. Afterward, many more ground-based [8] and mission observations on electrical and optical evidence of Venus lightning were reported [9]. The Venus Climate Orbiter (VCO) and Planet-C, observed an intense optical flash that was assigned to lightning in 2020 [10].

Electrons with high kinetic energy generated by Venusian lightning would collide with atmospheric gaseous molecules and dissociate, excite these radicals, including atoms and molecules at excited states, have high chemical activity. Electrochemical reactions among these species would create new species that would not be produced in common Venusian chemical reactions.

Experimental results

We conducted a series of simulation experiments on Venusian lightning in a newly designed Venus-ESD-Chamber (VEC). We report here the radicals detected during ESD in VEC under CO₂ and gas mixture of N₂, O₂, CO₂, H₂O, Ar. Different types of discharges would generate numbers of radical species which indicate that electrochemical reactions take place during and after discharge.

In collected plasma spectra of ESD in gas mixture, the emission lines of N₂, N₂⁺, N, N⁺, NO, OH, O, O⁺, A_r, and Ha were observed and may be generated by the following reactions:

 

N₂ + e → N₂^* + e             (1)

N₂ + e → N₂⁺ + e             (2)

N₂ + e → N + N + e            (3)

N + e → N⁺ + e               (4)

O₂ + e → O + O + e            (5)

O + e → O⁺ + 2e              (6)

N₂ + O → NO + N              (7)

H₂O + e → OH + H + e        (8)

Ar + e → Ar^* + e                   (9)

Emission lines of CO₂⁺, CO, CO⁺, C, C₂, C⁺, O, O⁺, and OH were observed in spectra of CO₂ electrostatic discharge, the possible electrochemical reactions are as follows:

CO₂ + e → CO₂^* + e                      (10)

CO₂ + e → CO₂⁺ + 2e                     (11)

CO₂ + e → CO + O + e                  (12)

CO₂ + e → C⁺ + O₂ + 2e                 (13)

CO₂ + e → CO⁺ + O + 2e               (14)

 

These active radicals would play significant rules in the evolutions of the Venusian atmosphere.

Further Work: For the next step, we will conduct ESD in SO₂ gas and in SO₂ + CO₂ gas with different concentrates for investigations of sulfur species generated in ESD.

 

Acknowledgments: This work was supported by the CSC scholarship (NO. 201906220244) for HKQ to support his joint-training Ph.D. study at Washington University in St. Louis, and by spectral funding 94351A of WUSTL_MCSS to AW to maintain a collaboration with planetary scientists and students from Shandong University in China.

 

Reference:

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[2]      K. H. Baines et al., Planet. Space Sci., 2009.

[3]      K. Aplin, Springer Science & Business Media, 2013.

[4]      W. M. Farrell and M. D. Desch, J. Geophys. Res. Planets, 2001.

[5]      W. W. L. Taylor, F. L. SCARF, C. T. RUSSELL, and L. H. BRACE, Nature, 1979.

[6]      R. Lorenz, J. Phys. IV, 2002.

[7]      L. V Ksanfomaliti, F. L. Scarf, and W. W. L. Taylor, Venus, 1983.

[8]      S. A. Hansell, W. K. Wells, and D. M. Hunten, Icarus, 1995.

[9]      R. D. Lorenz, Prog. Earth Planet. Sci., 2018.

[10]    Y. Takahashi et al., Nat. Portf., 2021.