Groundbased Studies of Io Volcanism


Starting in December 1989, we have been imaging thermal emission from Io's volcanos from earth-based telescopes at the NASA Infrared Telescope Facility in Hawaii, with an emphasis on good time resolution, high spatial resolution, and short wavelengths (1.7 - 5 microns). Observations have also been made at Lowell Observatory starting in 1995. Eclipses and occultations of Io by Jupiter are used to enhance sensitivity to faint volcanos and to provide spatial resolution across the disk, even in poor seeing.

Since 1995, we have obtained useful information on Io's volcanic activity on over 250 nights. Two large outbursts have been seen, and several smaller eruptions lasting a few weeks, at sites where activity had not been seen before.

Spencer also coordinated the Io portion of the IRTF Galileo Support Jupiter/Io Monitoring Program, which obtained regular infrared images of Io's volcanic activity between 1996 and 2001.

Whenever possible, we also obtained 1.6 - 5 micron images of Jupiter to support the Galileo mission. These were analyzed by Glenn Orton and his colleagues.


Click on thumbnails for full resolution versions.

Two Io hot spots being occulted by Jupiter, 3.8 microns, IRTF, 1990/10/12. (72 kbytes).

Six Io volcanos emerging in succession from behind Jupiter on August 26, 1995, at 3.5 microns. (266 K JPG). The color is artificial, and Jupiter, which is very dark due to CH4 absorption, has been artificially brightened.

Publications from the Ground-Based Program:

Spencer, J.R., M.A. Shure, M.E. Ressler, J.D. Goguen, W.M. Sinton, D. W. Toomey, A. Denault, and J. Westfall (1990). Discovery of hotspots on Io using disk-resolved infrared imaging. Nature 348 618-621.
Spencer, J. R., R. R. Howell, B. E. Clark, D. R. Klassen, and D. O'Connor (1992). Volcanic activity on Io at the time of the Ulysses encounter. Science, 257, 1507-1510.
Spencer, J. R., B. E. Clark, L. M. Woodney, W. M. Sinton, and D. Toomey (1994). Io hot spots in 1991: Results from Europa occultation photometry and infrared imaging. Icarus 107, 195-208.
Orton, G., and 37 co-authors including J. R. Spencer (1996). Preliminary results of earth-based observations of the Galileo probe entry site. Science 272,+ 839-840.
Spencer, J. R., J. A. Stansberry, C. Dumas, D. Vakil, R. Pregler, M. Hicks, and K. Hege (1997). A History of High-Temperature Io Volcanism: February 1995 to May 1997. Geophys. Res. Lett. 24, 2451-2454.
Stansberry, J. A., J. R. Spencer, R. R. Howell, C. Dumas, and D. Vakil (1997). Violent Silicate Volcanism on Io in 1996. Geophys. Res. Lett. 24, 2455-2458.
Blaney, D., G. Veeder, D. Matson, T. Johnson, J. Goguen, and J. Spencer (1997). Io's thermal anomalies: Clues to their origin from comparing ground based observations between 1 and 20 microns. Geophys. Res. Lett. 24, 2459-2462.
Ortiz, J.L., G.S. Orton, A.J. Friedson, S.T. Stewart, B.M. Fisher, and J.R. Spencer (1998). Evolution and persistence of 5-micron hot spots at the Galileo probe entry latitude. J. Geophys. Res. 103, 23051-23069.
Howell, R.R., J.R. Spencer, J. D. Goguen, F. Marchis, R. Prange, T. Fusco, D.L. Blaney, G.J. Veeder, J.A. Rathbun, G.S. Orton, A.J. Grocholsky, J.A. Stansberry, G.S. Kanner, E.K. Hege (2001). Ground-based observations of volcanism on Io in 1999 and early 2000. J. Geophys. Res. 106, 33129-33139.
Loki, Io: A periodic volcano. J. A. Rathbun, J. R. Spencer, A. G. Davies, R. R. Howell, and L. Wilson. Geophys. Res. Lett., in press, 2002. PDF format.


John Spencer, U. Hawaii and Lowell Observatory, 1989-present
Bill Sinton, U. Hawaii, 1979-1991
Beth Clark, U. Hawaii, 1991 - 1994
Christophe Dumas, U. Hawaii, 1995 - 1997
John Stansberry, Lowell Observatory, 1995 - 1999
Julie Rathbun, Lowell Observatory and University of Redlands, 1999 -
Kandis Lea Jessup, Lowell Observatory, 2002 -

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