No. 100: Jul-Aug 1995
Well, not Jupiter itself but its strange Galilean satellite Io. On July 26, 1983, Io suddenly brightened by about 50% for just under 2 minutes. The "flash" represented an emission of energy of some 1028 ergs, which is equivalent to the impact on the satellite of an ice mass 5-kilometers in diameter moving at 60 km/sec. This collision interpretation is encouraged by the 1994 impacts of cometary fragments on Jupiter proper. In the case of Io, however, there is another possibility: electrical arcing. Io's volcanoes are prodigious spewers of metallic sodium, and T. Gold has speculated that colossal arcs may occur in this conducting environment as Io cuts through Jupiter's magnetic field. (See Science Frontiers #10.
(O'Brien, Roger; "Has Jupiter Flashed Before?" British Astronomical Association, Journal, 104:6, 1994.)
Comment. Io is also noted for its erratic brightening after it emerges from Jupiter's shadow. For more on Io's so-called "post-eclipse brightening," see p. 67 in the book Science Frontiers and the catalog volume The Moon and the Planets, both described here.