On 6/7 November (revolution 722), the detectors of all the ISO instruments experienced particle impact rates some 10-20 times higher than usual. This resulted from increased solar activity; see the Space Environment Centre. ISO's real-time report for this revolution can be seen here. By rev 723, impact rates were again essentially within normal ranges and the instruments were functioning nominally. No other events in this time period have been seen by the ISO detectors.
All observations, taken with each of ISO's instruments on rev 722, are badly affected by impacts from high energy particles and are, effectively, useless for astronomy. A comparison of two CAM raster observations, taken during revolution 722 and a normal revolution, shows clearly the huge contamination. All observations have been made available for rescheduling. However, unfortunately, it will not be possible to repeat some of these observations as they are in regions of the sky that are no longer visible to ISO.
Detailed analyses of the impact of the Solar Flare on the ISO detectors can be found in the assessments from the Instrument Teams:
This is the first time in ISO's 24 month history that a such a dramatic event occurred, leading to loss of observations. While the solar activity has just started to increase there may be a chance of such an event re-occurring.
A.Heske
ISO Science Operations Team
25/11/97