Geological features on Earth
tell us that this latter type of
volcanism was widespread 1-2
billion years ago, during the era
when life was evolving. While
we can only infer what this activity looked like on Earth by
surface features created in the
distant past, we see such eruptions continuing on Io today,
allowing us, in a sense, to look
back in time.
Eruption temperatures can be
derived from near-infrared (2-5 micron) spectra, where we see the peak in thermal emission from objects with temperatures in the
600-1450 K range. Combining data from the
IRTF and Gemini N we extracted the eruption’s spectrum and modeled the event as
a multi-component system, including small
high-temperature eruption zones and larger,
cooler regions of spreading lava. We fit the
models to the spectrum to determine the
temperatures and emitting areas of the various components. Figure 4 shows the outburst
spectrum with model spectra for lava temperatures of 1475 K and 1900 K, corresponding to basaltic and ultramafic lava compositions, respectively.
Our modeling placed a lower bound on the
eruption temperature of 1200-1300 K with
best-fit temperatures above 1500 K. These
upper values indicate ultramafic magma
composition, but the difficulty of observing Io at the short wavelengths required to
constrain these temperatures means that
the upper bounds are highly uncertain. For
now, the question of Io’s dominant magma
composition remains an intriguing mystery
for future observations to settle.
Fountains of Lava
The high eruption temperatures we measured suggest freshly-exposed lava continu-
January 2015
ously gushing from an area of tens of square
kilometers. Ashley Davies, a member of our
team and a volcanologist at the Jet Propulsion Laboratory who specializes in Io, says
that the eruption most likely occurred in the
form of fire fountains erupting from long fissures along Io’s surface.
Figure 3.
The decline in the 3.8micron intensity of the
August 29th outburst,
derived from Gemini
observations. Figure
adapted from de Kleer
et al., 2014.
Volcanic events on Io range from bright
bursts that last only a few hours to hot spots
that persist for months or years. The neardaily observations at Gemini North in the
two weeks following the August 29th detection allowed us to watch the eruption’s
rapid decay in brightness as it transitioned
from vigorous lava fountaining to the resultant fluid flows that spread rapidly over
thousands of square kilometers of Io’s surface while slowly cooling. Figure 3 plots the
change in the eruption’s 3.8-micron brightness in the days following detection.
We measured a peak power of 15-25 terawatts
(TW), making this one of the most powerful
eruptions observed in the Solar System to
date. The highest-power eruption ever observed on Io was at the Surt volcano in 2001; it
emitted around 78 TW, a factor of a few above
this event (Marchis et al., 2002). Both of these
numbers completely overwhelm lava fountains we see on Earth today; for comparison,
the lava fountains associated with the 2010
eruption of Eyjafjallajökull emitted a peak of
only 1 gigawatt (Davies et al., 2013).
2014 Year in Review
GeminiFocus
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