TOPS Io Volcano Observations

On June 22 1999, during the 1999 TOPS student/teacher astronomy workshop in Waimea, Hawaii, I demonstrated some "live" astronomy by conducting a remote observing run on the NASA Infrared Telescope Facility (IRTF) from the Keck headquarters building in Waimea. The run was part of my long-term program to monitor volcanic activity on Jupiter's moon Io by observing the near-infrared volcanic radiation from the moon.

Pictures of the observing session

Taken by Karen Meech. Click on thumbnail for full-sized image.

We were very lucky to observe an unusually bright volcanic eruption on Io during the TOPS demonstration. I discovered the eruption during the first part of the observing run, which involved observing Io's passage into Jupiter's shadow (an eclipse) and then its disappearance behind Jupiter itself (an occultation). I made these observations at the IRTF, on the summit of Mauna Kea. While Io completed its two-hour passage behind Jupiter I drove from the summit down to Waimea so I could observe Io's reappearance from behind Jupiter with the TOPS participants.

[Stuff on the techniques used to be inserted here]

Results from the Observations

This was the fourth-brightest eruption that we have observed in our program of over 200 nights at the telescope, perhaps the tenth-brightest ever seen on Io, and the brightest for which we have obtained such high-quality observations. At some wavelengths, it is several times brighter than the brightest eruption observed on Io by the Galileo spacecraft. We have given the eruption the romantic name of 9906A.
By timing the disappearance and reappearance of the volcano behind Jupiter, we now have a fairly good idea of its location, which is at 20 W, 25 S, probably at a volcano named Catequil Patera.
A quick look at the data indicates that the amount of hot material exposed during the eruption was equivalent to a 2.5 mile diameter region at 1900 degrees Farenheit. This is a far bigger area of hot material than is exposed during the eruptions of Kilauea, for example.
Observations by Bob Howell at the Wyoming Infrared Observatory saw the same eruption again a week later. It had faded several-fold but was still the brightest eruption visible on Io. At the same time, the Galileo spacecraft took its closest-yet images of Io, which included a look at the location of the eruption. Galileo saw the eruption as a very bright glow in images taken, like many of our IRTF images, when Io was in Jupiter's shadow. We are still waiting to see if there is debris from the eruption blanketing the surrounding terrain, or a plume of material being blasted into space from the volcano. Both a plume and a debris blanket were seen during a similar or smaller eruption at the Io volcano Pillan that was observed by the Galileo spacecraft in 1997.

Sequence of images of Io volcano 9906A disappearing behind Jupiter. Sequence lasts 35 seconds, wavelength is 3.5 microns. The exact time of disappearance gives the location of the volcano on Io.
Click on the thumbnail for a full-sized version.

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