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Lunar and Planetary Science XXXIII (2002)
1455.pdf
COMPARING VOLCANIC ACTIVITY AND SURFACE CHANGES ON THE GALILEAN SATELLITE IO
AND A COMPARISON OF VOLCANIC ACTIVITY AND SURFACE CHANGES TO MONITOR TIDAL
HEATING ON THE JOVIAN MOON IO FROM 1996–2000: A Two-Year Study of Io. M. B. Totonchy,
1
Oregon Episcopal School (6300 SW Nicol Road, Portland, OR 97223)
Introduction:
Io is one of the four Galilean moons and one of
twenty-eight total moons of Jupiter. Io is the most volcanically active body in the solar system that we know
of and is dominated by sulfur dioxide and its products
[1]. Tidal heating suggests that Io’s orbital and thermal
evolution and interior structure are all linked [2]. Heating that takes place in the large deep mantle made up of
mostly silicate is called deep heat while heating which
is near the surface in the shallow asthenosphere made
up of partly molten silicate is called shallow heat. Io’s
volcanism is a continuum of high temperature events of
varying power output and duration.
Comparing Volcanic Activity and Surface
Changes on the Galilean Satellite Io:
The purpose of this project was to measure, compare and analyze the volcanic activity on Io observed
by Galileo and Voyager. Nine of the ten volcanoes
known to be active at the time of Voyager were compared to the same images of the volcanoes taken by
Galileo, 21 years later. The volcanoes analyzed were
Amirani, Maui, Prometheus, Volund, Isum, Marduk,
Pele, Daedalus, W.Pele, Loki, and Culann (this volcano was not active throughout both voyages, but has
experienced significant changes). Of the 30 hot spots
detected in the first four orbits of the Galileo Mission,
18 of them were new hot spots, 10 of them were previously known from Voyager data to be active and the
other 2 had been discovered by ground-based observations [3]. The changes over time were compared by
using stacks created from data images from both Voyager and Galileo of these nine volcanoes. The lighting
and resolution of the images were large factors, but
images were compared that were taken from both Voyager and Galileo that were taken at similar illuminations, phase angles, filters and formatted with similar
pixel dimensions. NIH-Image was used to perform the
measurements of certain areas, mostly of new lava deposits, x-y coordinates, and diameters of certain active
flows. Observations were made for each of the seven
stacks created, noting new calderas, lava flows, shadows and shapes observed from both the Voyager and
Galileo images. There are new lava flows occurring in
each of the stacks. Among the various observations
made between the stacks were shadows in the images,
new calderas formed, a shifting in ash rings and new
sulfur dioxide deposits. These results indicated
changes that determined that the amount of volcanic
activity on Io has increased during the 21-year period.
Comparison of Volcanic Activity and Surface
Changes to Monitor Tidal heating on the Jovian
Moon Io from 1996-2000:
The purpose of the project this year was to compare
volcanic activity and surface changes on Io between
1996 and 2000 using Galileo data, to see where tidal
heat was being deposited on Io to tell if the internal
heat of Io is deep or shallow. It is known that tides of
Io are creating most of the heat, which is causing constant volcanic activity, but the internal heat of Io is
unknown. Io’s tides are being squeezed by Jupiter’s
tides as Io orbits around Jupiter about every 1.8 days,
so the tides on Io are very large because of the pull
Jupiter is exerting on Io. These tides heat up because
of friction. Io has an elliptical orbit around Jupiter, so
this means that Io is going very fast when it is close to
Jupiter and slower farther away from Jupiter, which
could affect the internal heat of Io and where the tidal
heat is being deposited. It is hypothesized that the
internal heat of Io is deep, from which one would
predict greater volcanic activity near Io’s poles. Yet if
the internal heat of Io is shallow then it is hypothesized
that greater volcanic activity will occur all over Io,
with lots of smaller hotspots near the equatorial region.
The volcanic activity on Io was measured by
superimposing images from the different times between
1996 to 2000 and using data imagery in Scion image
programs to see where most of the volcanic activity
occurred. Filters, illumination/lighting, phase angle and
resolution were matched as close as possible between
each stack. New lava flows, new calderas and sulfur
dioxide deposits were analyzed to see where volcanism
accumulates on Io. The composition of Io’s plasma
torus changes from month to month and this may be because of volcanic activity on Io [2]. New lava flows, shadows, new calderas and sulfur dioxide deposits are in
the process of being analyzed to better understand the
activity of Io’s volcanoes during the five year period so
as to see where volcanism accumulates. By tracking
volcanic activity this could help explain why the
amount of dust in the Jovian System varies from month
to month, why the plasma torus varies in sulfur monoxide ion from one month to the next and why neutral
clouds vary in composition from one orbit to the next.
All of these problems could be linked to the amount of
Lunar and Planetary Science XXXIII (2002)
1455.pdf
STUDY OF IO: M. B. Totonchy
volcanic activity on Io from month to month, so by
tracking volcanic activity, we can compare months
where there was more volcanic activity to see if this
affected the amount of dust, sulfur monoxide or composition of neutral clouds. Hopefully correlations between volcanic activity and those variables will be
made. The data is in the process of being analyzed and
observations are being compared.
References:
[1] Geissler, P., McEwen A., lp, W., Belton, M.,
Johnson, T., Smythe, W., and Ingersoll, A. (1999).
Galileo Imaging of Atmospheric Emissions from Io.
Science, 285, 870- 873. [2] Spencer, J., and Schneider,
N. (1996). Io on the Eve of the Galileo Mission. Annual Review of Earth and Planetary Sciences, 24, 125183. [3] Lopes-Gautier, R., Davis, A.G., Carlson, R.,
Smythe, W., Kamp, L., Leader, F.E., Mehlman, R., and Galileo NIMS team. (1997). Hot spots on Io: Initial results from
Galileo’s near infrared mapping spectrometer. Geophysical
Research Letters, 24, 2439-2442.