The occurrence of lightning in a planetary atmosphere leads to chemical processes, which would not occur under standard temperatures and pressures. Lightning breaks up molecules into single fragments that can then join to form other chemical substances, resulting in a changed composition of the atmosphere. On Earth, lightning is important for the production of nitric oxides, which play a dominant role in the generation of pre-biotic molecules.
From the magnetometer data of VEXMAG, lightning was proved to occur in the Venus atmosphere, which was not really sure from previous missions. Venus Express now proved that there is in fact lightning activity all over the planet. The VEXMAG high-resolution data show bursts of electromagnetic waves in the upper ionosphere, being produced by lightning in the lower atmosphere.
Our sound track allows to hear the typical effect of the so-called "whistlers" generated by lightning: we transformed the measured electromagnetic frequencies into audible sound-waves. The typical frequency variation starts with a high tune, followed by lower ones, sounding like a whistle. The effect is due to the dispersional propagation of waves in the Venus atmosphere: high frequency waves move faster and therefore reach the upper layers (and VEXMAG) first, lower frequencies arrive later. The same effect is found on Earth: a short wave receiver allows hearing the whistlers from lightning on the other side of the Earth.
- Animation of lightning in the Venus atmosphere