Sprite discharges on Venus and Jupiter‐like planets: A laboratory investigation

Abstract

[1] Large sprite discharges at high atmospheric altitudes have been found to be physically similar to small streamer discharges in air at sea level density. Based on this understanding, we investigate possible sprite discharges on Venus or Jupiter-like planets through laboratory experiments on streamers in appropriate CO 2 -N 2 and H 2 -He mixtures. First, the scaling laws are experimentally confirmed by varying the density of the planetary gasses. Then, streamer diameters, velocities, and overall morphology are investigated for sprites on Venus and Jupiter; they are quite similar to those on Earth, but light emissions in the visible range are fainter by 2 orders of magnitude. The discharge spectra are measured; they are dominated by the minority species N 2 on Venus and by the majority species H 2 on Jupiter-like planets. The spectrum of a fully developed spark on Venus is measured. We show that this spectrum is significantly different from the expected sprite spectrum.

Probing photo-ionization: simulations of positive streamers in varying N2 : O2-mixtures

“…The presence of this ionizing radiation with significant penetration length in air was demonstrated in numerous experiments [18]. A similar mechanism was proposed by Dubrovin et al in section 2.2 of [16] for the H 2 :He mixtures on Jupiter-like planets; she argues that there are electronically excited He states that can emit photons with sufficient energy to ionize H 2 while no such mechanism exists for Venus (CO 2 :N 2 ). However, the only quantitative photo-ionization model exists for the moment, to our best knowledge, for N 2 :O 2 mixtures like air [19].…”

“…While most work focusses on positive streamers in air, positive streamers have been observed in varying nitrogen:oxygen ratios [11,12,13,14], in argon [15] as well as in gas mixtures presenting the atmospheres of Venus (CO 2 :N 2 ) and of Jupiter-like gas giants (H 2 :He) [16]. In a recent experiment [14], positive streamers were observed in nitrogen, oxygen and argon with impurity levels below 1 ppm; they propagate with essentially the same velocity as in air, but are thinner and less straight, they branch more, move more in a zigzag fashion or even can form feathery structures.…”

“…But photoionization according to the traditional model critically depends on the ratio between oxygen and nitrogen and should completely stop when either nitrogen or oxygen are absent. For H 2 :He mixtures (as in the atmospheres of the planetary gas giants) a photo-ionization model has been outlined in [16], but a photo-ionization mechanism on Venus (CO 2 :N 2 ) is unlikely to exist [16], and in pure gases it cannot exist either. An alternative is propagation through background ionization, this background can be generated by radiation or by previous discharges in a mode of repetitive pulses [17].…”

Positive streamers in air of varying density: experiments on the scaling of the excitation density

“…We estimated S(λ) by measuring the spectrum of a streamer and glow discharge at low pressures (50 to 200 mbar, Figure A1). The spectrum was recorded using three small Ocean Optics spectrometers together spanning the wavelength range of 230-940 nm, at several pressures and voltages, similarly to Dubrovin et al [50]. This spectrum is similar to measured and calculated sprite and streamer spectra (see e.g.…”

Space charge effects and arc properties of simulated lightning on Venus

“…In the Venus atmosphere hardly any streamers were observed, at the most a single one was seen at the front of the propagating leader. Dubrovin et al [2010] also found that streamers are very difficult to produce in a Venus Atmosphere above 0.8 bar (608 torr). These observations suggest that in high-pressure gases containing CO 2 the streamers do not play a significant role in the propagation of the discharge.…”