Active Volcanism on Io as Seen by Galileo SSI

Alfred S. McEwen, Laszlo Keszthelyi, Paul Geissler, Damon P. Simonelli, Michael H. Carr, Torrence V. Johnson, Kenneth P. Klaasen, H. Herbert Breneman, Todd J. Jones, James M. Kaufman, Kari P. Magee, David A. Senske, Michael J S Belton, Gerald Schubert

Research output: Contribution to journalArticle

135 Citations (Scopus)

Abstract

Active volcanism on Io has been monitored during the nominal Galileo satellite tour from mid 1996 through late 1997. The Solid State Imaging (SSI) experiment was able to observe many manifestations of this active volcanism, including (1) changes in the color and albedo of the surface, (2) active airborne plumes, and (3) glowing vents seen in eclipse. About 30 large-scale (tens of kilometers) surface changes are obvious from comparison of the SSI images to those acquired by Voyager in 1979. These include new pyroclastic deposits of several colors, bright and dark flows, and caldera-floor materials. There have also been significant surface changes on Io during the Galileo mission itself, such as a new 400-km-diameter dark pyroclastic deposit around Pillan Patera. While these surface changes are impressive, the number of large-scale changes observed in the four months between the Voyager 1 and Voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive. There are two reasons why this was not actually the case. First, it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years. Second, it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of Io's surface. The plume monitoring has revealed 10 active plumes, comparable to the 9 plumes observed by Voyager. One of these plumes was visible only in the first orbit and three became active in the later orbits. Only the Prometheus plume has been consistently active and easy to detect. Observations of the Pele plume have been particularly intriguing since it was detected only once by SSI, despite repeated attempts, but has been detected several times by the Hubble Space Telescope at 255 nm. Pele's plume is much taller (460 km) than during Voyager 1 (300 km) and much fainter at visible wavelengths. Prometheus-type plumes (50-150 km high, long-lived, associated with high-temperature hot spots) may result from silicate lava flows or shallow intrusions interacting with near-surface SO2. A major and surprising result is that ~30 of Io's volcanic vents glow in the dark at the short wavelengths of SSI. These are probably due to thermal emission from surfaces hotter than 700 K (with most hotter than 1000 K), well above the temperature of pure sulfur volcanism. Active silicate volcanism appears ubiquitous. There are also widespread diffuse glows seen in eclipse, related to the interaction of energetic particles with the atmosphere. These diffuse glows are closely associated with the most active volcanic vents, supporting suggestions that Io's atmopshere is dominated by volcanic outgassing. Globally, volcanic centers are rather evenly distributed. However, 14 of the 15 active plumes seen by Voyager and/or Galileo are within 30° of the equator, and there are concentrations of glows seen in eclipse at both the sub- and antijovian points. These patterns might be related to asthenospheric tidal heating or tidal stresses. Io will continue to be observed during the Galileo Europa Mission, which will climax with two close flybys of Io in late 1999.

Original languageEnglish (US)
Pages (from-to)181-219
Number of pages39
JournalIcarus
Volume135
Issue number1
DOIs
StatePublished - Sep 1998

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Io
plumes
volcanism
plume
solid state
volcanology
vents
eclipses
Prometheus
pyroclastic deposit
calderas
deposits
caldera
silicates
Galileo project
silicate
hot surfaces
wavelength
orbits
color

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

McEwen, A. S., Keszthelyi, L., Geissler, P., Simonelli, D. P., Carr, M. H., Johnson, T. V., ... Schubert, G. (1998). Active Volcanism on Io as Seen by Galileo SSI. Icarus, 135(1), 181-219. https://doi.org/10.1006/icar.1998.5972

Active Volcanism on Io as Seen by Galileo SSI. / McEwen, Alfred S.; Keszthelyi, Laszlo; Geissler, Paul; Simonelli, Damon P.; Carr, Michael H.; Johnson, Torrence V.; Klaasen, Kenneth P.; Breneman, H. Herbert; Jones, Todd J.; Kaufman, James M.; Magee, Kari P.; Senske, David A.; Belton, Michael J S; Schubert, Gerald.

In: Icarus, Vol. 135, No. 1, 09.1998, p. 181-219.

Research output: Contribution to journalArticle

McEwen, AS, Keszthelyi, L, Geissler, P, Simonelli, DP, Carr, MH, Johnson, TV, Klaasen, KP, Breneman, HH, Jones, TJ, Kaufman, JM, Magee, KP, Senske, DA, Belton, MJS & Schubert, G 1998, 'Active Volcanism on Io as Seen by Galileo SSI', Icarus, vol. 135, no. 1, pp. 181-219. https://doi.org/10.1006/icar.1998.5972
McEwen AS, Keszthelyi L, Geissler P, Simonelli DP, Carr MH, Johnson TV et al. Active Volcanism on Io as Seen by Galileo SSI. Icarus. 1998 Sep;135(1):181-219. https://doi.org/10.1006/icar.1998.5972
McEwen, Alfred S. ; Keszthelyi, Laszlo ; Geissler, Paul ; Simonelli, Damon P. ; Carr, Michael H. ; Johnson, Torrence V. ; Klaasen, Kenneth P. ; Breneman, H. Herbert ; Jones, Todd J. ; Kaufman, James M. ; Magee, Kari P. ; Senske, David A. ; Belton, Michael J S ; Schubert, Gerald. / Active Volcanism on Io as Seen by Galileo SSI. In: Icarus. 1998 ; Vol. 135, No. 1. pp. 181-219.
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T1 - Active Volcanism on Io as Seen by Galileo SSI

AU - McEwen, Alfred S.

AU - Keszthelyi, Laszlo

AU - Geissler, Paul

AU - Simonelli, Damon P.

AU - Carr, Michael H.

AU - Johnson, Torrence V.

AU - Klaasen, Kenneth P.

AU - Breneman, H. Herbert

AU - Jones, Todd J.

AU - Kaufman, James M.

AU - Magee, Kari P.

AU - Senske, David A.

AU - Belton, Michael J S

AU - Schubert, Gerald

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N2 - Active volcanism on Io has been monitored during the nominal Galileo satellite tour from mid 1996 through late 1997. The Solid State Imaging (SSI) experiment was able to observe many manifestations of this active volcanism, including (1) changes in the color and albedo of the surface, (2) active airborne plumes, and (3) glowing vents seen in eclipse. About 30 large-scale (tens of kilometers) surface changes are obvious from comparison of the SSI images to those acquired by Voyager in 1979. These include new pyroclastic deposits of several colors, bright and dark flows, and caldera-floor materials. There have also been significant surface changes on Io during the Galileo mission itself, such as a new 400-km-diameter dark pyroclastic deposit around Pillan Patera. While these surface changes are impressive, the number of large-scale changes observed in the four months between the Voyager 1 and Voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive. There are two reasons why this was not actually the case. First, it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years. Second, it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of Io's surface. The plume monitoring has revealed 10 active plumes, comparable to the 9 plumes observed by Voyager. One of these plumes was visible only in the first orbit and three became active in the later orbits. Only the Prometheus plume has been consistently active and easy to detect. Observations of the Pele plume have been particularly intriguing since it was detected only once by SSI, despite repeated attempts, but has been detected several times by the Hubble Space Telescope at 255 nm. Pele's plume is much taller (460 km) than during Voyager 1 (300 km) and much fainter at visible wavelengths. Prometheus-type plumes (50-150 km high, long-lived, associated with high-temperature hot spots) may result from silicate lava flows or shallow intrusions interacting with near-surface SO2. A major and surprising result is that ~30 of Io's volcanic vents glow in the dark at the short wavelengths of SSI. These are probably due to thermal emission from surfaces hotter than 700 K (with most hotter than 1000 K), well above the temperature of pure sulfur volcanism. Active silicate volcanism appears ubiquitous. There are also widespread diffuse glows seen in eclipse, related to the interaction of energetic particles with the atmosphere. These diffuse glows are closely associated with the most active volcanic vents, supporting suggestions that Io's atmopshere is dominated by volcanic outgassing. Globally, volcanic centers are rather evenly distributed. However, 14 of the 15 active plumes seen by Voyager and/or Galileo are within 30° of the equator, and there are concentrations of glows seen in eclipse at both the sub- and antijovian points. These patterns might be related to asthenospheric tidal heating or tidal stresses. Io will continue to be observed during the Galileo Europa Mission, which will climax with two close flybys of Io in late 1999.

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