[Previous] | [Session 11] | [Next]
J. Caldwell (York University), W. Borucki, K. Rages (NASA Ames)
Both Voyager and Galileo spacecraft have observed large, energetic lightning storms on the nightside of Jupiter. The geographical distribution and intensity of the storms are substantially different than those of terrestrial storms, and raise questions about both the nature of the lightning activity and the dynamical properties of the Jovian atmosphere. If lightning activity could be observed systematically from Earth-based or Earth-orbiting observatories rather than spacecraft near Jupiter, the much longer time coverage available would answer some of these questions.
An attempt was made to observe lightning activity on the dayside of Jupiter with the Wide Field Planetary Camera of the Hubble Space Telescope operating in the PC mode. Because laboratory observations have shown that the most prominent emission feature of a simulated lightning flash in a Jovian atmospheric environment is the hydrogen H alpha line, we used the narrowband HST filter (F656N) centered at that wavelength. This filter strongly increases the signal (lightning) to noise (reflected sunlight) ratio because the reflected Solar Fraunhofer line is much broader than the planetary emission line, and because the line is strongly in absorption in the solar spectrum. A range of exposure times centered around 1 sec was used to optimize the contrast between the brief flashes and the steady continuum.
A few features that could be lightning were seen after shifting and adding thirty-five images, but no convincing evidence was found.