Observatory atop Hawaii’s Mauna Kea (long
dormant) volcano to target the atmosphere
of Uranus. When she finished, de Pater decided to take brief images of Io in anticipation
of our team beginning a program to monitor
Io in the near-infrared at the Gemini North
telescope and NASA’s Infrared Telescope Facility (IRTF), also located on Mauna Kea.
The Keck images revealed a pair of incredibly
bright eruptions near Io’s south pole. These
events fall into the rare “outburst” class of Ionian volcanoes. They represent the hottest
and most energetic volcanic activity on the
moon but are typically seen only once every
year or two. Both the Gemini N and IRTF telescopes scheduled follow-up observations
through Director’s Discretionary Time in the
subsequent days to watch the events evolve.
The first follow-up observations, made simultaneously at the IRTF and Gemini North
telescopes, revealed something unexpected
and even more incredible: a third eruption,
far from the site of the previous ones. This
new event was both brighter
and more powerful than the
initial pair combined. Figure
1 shows images at multiple
wavelengths from the Keck
detection of the first two eruptions on August 15th alongside
the Gemini detection on August 29th of the third.
Looking into Earth’s Distant Past
Volcanism is one of the few processes linking the hidden interior of a planet with the
observable exterior. It is therefore one of
the few ways of learning about what’s happening inside planets. The question of Io’s
dominant magma composition is still unanswered, but is important for understanding
how Io’s interior translates tidal forcing into
volcanic eruptions.
Does Io erupt basaltic lavas similar to those
we see on Earth (at Hawaii’s Kilauea volcano,
for example), or is the magma composition
different? By determining the peak temperatures reached by volcanic eruptions, we can
constrain which minerals might exist in melt
form. Basaltic magmas erupt at a temperature near 1475 Kelvin (K). Higher temperatures could indicate runnier magnesium-rich
magmas of an ultramafic composition that
require a higher internal heat to melt, such
as Earth had when it first formed.
Figure 2.
Observations of the
August 29th volcanic
outburst on Io over
a two-week period.
The star indicates the
outburst site; other
smaller-scale events
are also visible. Figure
adapted from de Kleer
et al., 2014.
Over the following two weeks,
Gemini scheduled near-nightly imaging of Io to follow the
course of the third eruption
(Figure 2); the first three of
which were conducted simultaneously with the IRTF. These
near-daily observations, utilizing a combination of Gemini’s
adaptive optics and the spectral information from the IRTF
data, gave us unprecedented
coverage of this rare event.
October 2014
GeminiFocus
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