The Volcanoes of Io

An interactive exercise enlisting students

Here is the lightcurve data that I've gathered so far: quality is variable but the March 2nd outburst really stands out! I've included enough text to hopefully explain everything.

Best wishes,
John.

The following table gives John Spencer's measurements of the volcanic activity on Io in February and March 1995, calculated from the brightness of Io at the infrared wavelength of five microns during the Jason Project. The first and second columns give the date and time of each observation, and the third column gives the longitude of the center of Io's disk, at that date and time, in degrees. The fourth column gives the brightness of Io's volcanos at time and longitude. Io's brightness is measured in the same units that are used in the graph of the old 1989/1990 data in the curriculum, so if you plot central longitude on the x axis and volcano brightness on the y axis you will get a graph that you can compare directly with the 1989/1990 data to see how the volcanic activity has changed since then. The graph will also give you an idea of the longitude on Io where the most active volcanos are located at present.

------------------------------------------------------------------
        Universal  Central    Measured 5-micron Volcano Brightness,
  Date     Time   Longitude   Watts per square meter per micron
------------------------------------------------------------------
02/26/95  15:29      332                0.011  
02/27/95  18:51      204                0.006  
02/28/95  20:24       60                0.067  
03/01/95  18:05      243                0.019  
03/01/95  19:43      257                0.000  
03/02/95  15:30       65                0.097  
03/02/95  18:04       86                0.129
03/08/95  16:10      212                0.002  
03/08/95  19:23      239                0.013  
------------------------------------------------------------------

This file will be updated as new measurements are made and analysed.

ADVANCED TOPIC:

For those who are interested in the meaning of the units "Watts per square meter per micron" that are used to measure the volcano brightness on Io, this unit measures the amount of heat energy that would be radiated, on average, from every square meter of Io's surface at infrared wavelengths between 4.5 and 5.5 microns, if the volcanos that we see were spread evenly over the whole satellite instead of concentrated in a few places. You might want to look up how much interior heat energy comes out of every square meter of the Earth's surface, on average, to compare with this number. Io radiates a lot of additional volcanic heat at longer infrared wavelengths, but our infrared camera isn't sensitive to longer wavelengths than five microns, so it can't detect this additional heat.

The Volcanoes of Io

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Gene Carl Feldman (gene@seawifs.gsfc.nasa.gov) (301) 286-9428
Todd Carlo Viola, JASON Foundation for Education (todd@jason.org)