Extra-terrestrial sprites: laboratory investigations in planetary gas mixtures

We investigate streamers in gas mixtures representing the atmospheres of Jupiter, Saturn (H2-He) and Venus (CO2-N2). Streamer diameters, velocities, radiance and overall morphology are investigated with fast ICCD camera images. We confirm experimentally the scaling of streamer diameters in these gases by studying streamers with minimal diameters. The brightness of laboratory streamers is investigated, and a scaling model for atmospheric sprites is proposed. Fitting the scaling model with measurements, we give an estimate of minimal sprite brightness on Earth, Jupiter and Saturn. The estimated brightness of terrestrial sprites agrees well with observations and with existing models, and may serve as a benchmark for space-based observations of TLEs by planetary missions such as Cassini and Juno.