  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 CO2-N2 and H2-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 two orders of magnitude.
The discharge spectra are measured; they are dominated by the minority species
N2 on Venus, while signatures of both species are found 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.
