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Observing Io's Volcanos During the Comet Crash Period


For those with infrared cameras or photometers who have time during the impact observations, there is a chance to do some useful monitoring of Io's volcanos. Io will be eclipsed and occulted by Jupiter at the times in the following table. Time-resolved infrared photometry (2.3 microns or longer) of Jupiter occultation egress, which occurs in Jupiter's shadow, will give a 100-km resolution view of the spatial distribution of volcanic thermal emission across Io. Time resolution of a second or slower is useful. With the methane filters that everyone has handy for the comet crash, this is an easy observation at 2.3, 3.5, or 3.8 microns, and is good practice for the similar time-critical crash observations.

Io emerges from behind Jupiter about 14 arcsec E, 11 arcsec S, from the center of the disk.

It's also worth observing the Jupiter occultation ingress, which occurs in sunlight, especially at the longer wavelengths, as the occultation of bright volcanic hot spots, if any, can be seen even in sunlight.

Absolute calibration of the photometry is useful to have.

During the period of > 1 hour that Io is visible in Jupiter's shadow after occultation egress but before eclipse egress, multicolor photometry of the volcanic thermal emission is also valuable, at wavelengths of 1.7 microns or longer. If seeing is very much better than 1 arcsec, it is possible to directly resolve individual hot spots on the 1 arcsecond disk during this period.

In May there was a 5-10 fold brightening of the volcanic thermal emission that lasted less than a few weeks: here is a chance to look for similar dramatic changes, or more subtle ones, during the most intensive monitoring of the Jupiter system that is ever likely to occur.

Send questions or results to John Spencer,

       Occultation Ingress   Occultation Egress    
 UT    -------------------   ------------------    Eclipse
Date     Start     End         Start     End       Egress
7/15   02:11:04  02:14:52    04:22:20  04:26:09     05:40
7/16   20:39:20  20:43:08    22:50:39  22:54:27     00:09*
7/18   15:07:47  15:11:35    17:19:09  17:22:57     18:38
7/20   09:36:13  09:40:01    11:47:38  11:51:25     13:07
7/22   04:04:47  04:08:35    06:16:14  06:20:02     07:36
7/23   22:33:19  22:37:07    00:44:49* 00:48:36*    02:04*

*Following Day

Occultation times are accurate to about 1 second. Eclipse egress times are taken from the Astronomical Almanac and are good to about 2 minutes.

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