Summary of Results of the IRTF Galileo Support Io Monitoring Program

Reported as of March 31 2000.

Report on the IRTF Galileo Support Io Monitoring Program, 1995-1999

DATASET:

Total number of nights with useful Io images: 
112
Number of nights where images have been visually  inspected and for which large outbursts could have been detected: 
108

 RESULTS:

Number of large outbursts seen in images and photometry: 
2 (on 95/09/27, 99/08/02)
Number of nights when other, fainter, hotspots were seen (excluding Loki): 
13

The primary purpose of this program is to detect the brightest Io eruptions, termed "outbursts".  These events are the most likely to have an effect on Io's surface or Jupiter's magnetosphere, but are too brief to have much chance of being detected by Galileo itself.  They are also too brief for the IRTF Galileo support program to detect most of them, but any that it does detect during the Galileo mission can be correlate with Galileo remote sensing and magnetospheric data.

By the luck of the draw, we have detected one outburst on 95/09/27, shortly after this program started (thus demonstrating the program's
outburst-detecting capabilities), but only one has been seen during the Galileo orbital tour which started in December 1995, that one was first detected by Bob Howell at WIRO and observed at the IRTF following his notifying the TOs.  We have added considerably to the knowledge of outburst frequency
(important for assessing Io resurfacing rates: Blaney et al. 1995, "Volcanic eruptions on Io: Heat flow, resurfacing, and lava
composition", Icarus 113, 220), as shown in the following table:
 
Outburst Frequency
Observers
Dates
Number of Nights
Number of 
Outbursts Seen
Witteborn et al.
1978-1981
16
1
Sinton et al. 
1979-1988
69
1
Johnson et al.
1982-1993 
55
2
Spencer et al.
1989-1995
56
1
Howell et al. 
1985-1995
96
0
IRTF Galileo support
1995-1999
108
1
Totals  
400
6

This table does not include the August 1999 outburst, as it was only observed by NSFCAM because an outburst was known to be occurring.  The Galileo support program has provided 25% of the data in this table, and has detected 28% of all outbursts ever seen (including the August 1999 event): substantial contributions for a ten-minute-per-night program.

The other, fainter, hot spots that have been detected by this program require more image analysis than has been done so far for accurate determination of locations and fluxes, but the data are available for this work to be done when time permits.

SUMMARY

The IRTF Galileo Support Io monitoring program has made a substantial contribution to our knowledge of outburst frequency on Io, and it is
just dumb luck that it has not detected any large outbursts so far during the Galileo tour.  If continued for the remainder of the Galileo
extended mission, through the end of 1999, there is a good chance of detecting outbursts that could be used to determine the possible effects
of such outbursts on Io and the Jovian magnetosphere.  Even data that does not show outbursts can provide useful additional data on the
duration of hot spots seen by Galileo, or can pick up hot spots missed by Galileo.  I therefore recommend that the Galileo Support Io monitoring program be continued through the end of 1999.

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