Surface changes on Io during the Galileo mission

Paul Geissler, Alfred S. McEwen, Cynthia Phillips, Laszlo Keszthelyi, John Spencer

Research output: Contribution to journalArticle

49 Citations (Scopus)

Abstract

A careful survey of Galileo SSI global monitoring images revealed more than 80 apparent surface changes that took place on Io during the 5 year period of observation, ranging from giant plume deposits to subtle changes in the color or albedo of Patera surfaces. Explosive volcanic activity was discovered at four previously unrecognized centers: an unnamed patera to the south of Karei that produced a Pele-sized red ring, a patera to the west of Zal that produced a small circular bright deposit, a large orange ring detected near the north pole of Io, and a small bright ring near Io's south pole. Only a handful of Io's many active volcanoes produced large scale explosive eruptions, and several of these erupted repeatedly, leaving at least 83% of Io's surface unaltered throughout the Galileo mission. Most of the hot spots detected from SSI, NIMS and ground-based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period. Surface changes were found at every location where active plumes were identified, including Acala which was never seen in sunlight and was only detected through auroral emissions during eclipse. Two types of plumes are distinguished on the basis of the size and color of their deposits, confirming post-Voyager suggestions by McEwen and Soderblom [Icarus 55 (1983) 191]. Smaller plumes produce near-circular rings typically 150-200 km in radius that are white or yellow in color unless contaminated with silicates, and frequently coat their surroundings with frosts of fine-grained SO2. The larger plumes are much less numerous, limited to a half dozen examples, and produce oval, orange or red, sulfur-rich rings with maximum radii in the north-south direction that are typically in the range from 500 to 550 km. Both types of plumes can be either episodic or quasi-continuous over a five year period. Repeated eruptions of the smaller SO2-rich plumes likely contribute significantly to Io's resurfacing rate, whereas dust ejection is likely dominated by the tenuous giant plumes. Both types of plume deposits fade on time-scales of months to years through burial and alteration. Episodic seepages of SO2 at Haemus Montes, Zal Montes, Dorian Montes, and the plateau to the north of Pillan Patera may have been triggered by activity at nearby volcanic centers.

Original languageEnglish (US)
Pages (from-to)29-64
Number of pages36
JournalIcarus
Volume169
Issue number1
DOIs
StatePublished - May 2004

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Galileo project
Io
plumes
plume
deposits
rings
color
volcanic eruptions
explosive
volcanology
poles
volcanic eruption
Galileo (spacecraft)
seepage
radii
eclipses
sunlight
albedo
ejection
volcanoes

Keywords

  • Io
  • Satellite
  • Surfaces
  • Volcanism

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Geissler, P., McEwen, A. S., Phillips, C., Keszthelyi, L., & Spencer, J. (2004). Surface changes on Io during the Galileo mission. Icarus, 169(1), 29-64. https://doi.org/10.1016/j.icarus.2003.09.024

Surface changes on Io during the Galileo mission. / Geissler, Paul; McEwen, Alfred S.; Phillips, Cynthia; Keszthelyi, Laszlo; Spencer, John.

In: Icarus, Vol. 169, No. 1, 05.2004, p. 29-64.

Research output: Contribution to journalArticle

Geissler, P, McEwen, AS, Phillips, C, Keszthelyi, L & Spencer, J 2004, 'Surface changes on Io during the Galileo mission', Icarus, vol. 169, no. 1, pp. 29-64. https://doi.org/10.1016/j.icarus.2003.09.024
Geissler P, McEwen AS, Phillips C, Keszthelyi L, Spencer J. Surface changes on Io during the Galileo mission. Icarus. 2004 May;169(1):29-64. https://doi.org/10.1016/j.icarus.2003.09.024
Geissler, Paul ; McEwen, Alfred S. ; Phillips, Cynthia ; Keszthelyi, Laszlo ; Spencer, John. / Surface changes on Io during the Galileo mission. In: Icarus. 2004 ; Vol. 169, No. 1. pp. 29-64.
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