Images
of Io obtained at different infrared wavelengths (in microns, μm, or
millionths of a meter) with the W. M. Keck Observatory's 10-meter Keck
II telescope on Aug. 15, 2013 (a-c) and the Gemini North telescope on
Aug. 29, 2013 (d). The bar on the right of each image indicates the
intensity of the infrared emission. Note that emissions from the large
volcanic outbursts on Aug. 15 at Rarog and Heno Paterae have
substantially faded by Aug. 29. A second bright spot is visible to the
north of the Rarog and Heno eruptions in c and to the west of the
outburst in d. This hot spot was identified as Loki Patera, a lava lake
that appeared to be particularly active at the same time. An even
brighter outburst is seen to the lower right in panel (d), labeled
“201308C” and is one of the most powerful outbursts ever seen on Io. Credit: Imke de Pater and Katherine de Kleer, UC Berkeley.
Mauna Kea, Hawaii — Three massive volcanic eruptions
occurred on Jupiter's moon Io within
a two-week period, leading astronomers to speculate that these presumed
rare "outbursts," which can send material hundreds of miles above the
surface, might be much more common than previously thought. The
observations were made using the W. M. Keck Observatory and Gemini
Observatory, both near the summit of Mauna Kea, Hawaii.
"We typically expect one huge outburst every one or two years, and they're
usually not this bright," said Imke de Pater, professor and chair of
astronomy at the University of California, Berkeley, and lead author of one of two
papers describing the eruptions. "Here we had three extremely bright
outbursts, which suggest that if we looked more frequently we might see many
more of them on Io."
Io, the innermost of Jupiter's four large "Galilean" moons, is about 2,300
miles across, and, aside from Earth, is the only known place in the solar
system with volcanoes erupting extremely hot
lava like that seen on Earth. Because of Io's low gravity, large volcanic eruptions produce an
umbrella of debris that rises high into space.
De Pater's long-time colleague and coauthor Ashley Davies, a volcanologist with
NASA's Jet Propulsion Laboratory at the California Institute of Technology in
Pasadena, Calif., said that the recent eruptions resemble past events that spewed tens
of cubic miles of lava over hundreds of square miles in a short period of time.
"These new events are in a relatively rare class of eruptions on Io
because of their size and astonishingly high thermal emission," he said.
"The amount of energy being emitted by these eruptions implies lava
fountains gushing out of fissures at a very large volume per second, forming
lava flows that quickly spread over the surface of Io."
All three events, including the largest, most powerful eruption of the trio on
29 Aug. 2013, were likely characterized by “curtains of fire," as lava blasted
out of fissures perhaps several miles long.
The papers, one with lead author Katherine de Kleer, a UC Berkeley graduate
student, and coauthored by UC Berkeley research astronomer Máté Ádámkovics, and
the other coauthored by Ádámkovics and David R. Ciardi of Caltech's NASA
Exoplanet Science Institute, have been accepted for publication in the journal Icarus.
Lava fountains on Io
De Pater discovered the first two massive eruptions on Aug. 15, 2013, using the near-infrared camera (NIRC2) coupled to the
adaptive optics system on the Keck II telescope, one of two 10-meter telescopes
operated by the W. M. Keck Observatory in Hawaii. The brightest, at a caldera named
Rarog Patera, was calculated to have produced a 50 square-mile, 30-foot thick
lava flow, while the other, close to another caldera called Heno Patera,
produced flows covering 120 square miles. Both were located in Io's southern hemisphere, near its limb, and
were nearly gone when imaged five days later.
De Pater discovered a third and even brighter eruption — one of the brightest
ever seen on Io — on Aug. 29 at the start of a year-long series of Io
observations led by de Kleer, using both the Near-Infrared Imager with adaptive
optics on the Gemini North telescope on Mauna Kea, and the SpeX near-infrared
spectrometer on NASA's nearby
Infrared Telescope Facility (IRTF). De Kleer used the fortuitous detection of
this outburst simultaneously at Gemini and the IRTF to show that the eruption
temperature is likely much higher than typical eruption temperatures on Earth
today, "indicative of a composition of the magma that on Earth only
occurred in our planet’s formative years," de Kleer said.
At the time of the observation, the thermal source had an area of up to 32
square miles. The modelled temperature of the lava indicated it had barely had
time to cool, suggesting that the event was dominated by lava fountains.
"We are looking at several cubic miles of lava in rapidly emplaced
flows," said Davies, who has developed models to predict the volume of
magma erupted based on spectroscopic observations. "This will help us
understand the processes that helped shape the surfaces of all the terrestrial
planets, including Earth, and the moon."
The team tracked the heat of the third outburst for almost two weeks after its
discovery to investigate how volcanoes influence Io’s atmosphere and how these
eruptions feed a doughnut of ionized gas - the Io plasma torus - that surrounds
Jupiter near Io’s orbit. De Kleer timed her Gemini and IRTF observations to
coincide with observations of the plasma torus by the Japanese HISAKI
(SPRINT-A) spacecraft,
which is in orbit around Earth, so she can correlate the different data sets.
A volcanic laboratory
Volcanoes were first noted on Io in 1979, and subsequent studies by the Galileo
spacecraft, which first flew by Io in 1996, and ground-based telescopes show
that eruptions and lava fountains occur constantly, creating rivers and lakes
of lava. But large eruptions, creating vast lava flows in some cases thousands of
square miles in area, were thought to be rare. Only 13 were observed between
1978 and 2006, in part because only a handful of astronomers, de Pater among
them, regularly scan the moon.
Davies' interest in Io's volcanoes arises from the moon's resemblance to an early
Earth when heat from the decay of radioactive elements — much more intense than
radiogenic heating today — created exotic, high-temperature lavas. Io remains volcanically
active for a different reason — Jupiter and the moons Europa and Ganymede constantly
tug on it — but the current eruptions on Io are likely similar to those that shaped
the surfaces of inner solar system planets such as Earth and Venus in their
youth.
"We are using Io as a volcanic laboratory, where we can look back into the
past of the terrestrial planets to get a better understanding of how these
large eruptions took place, and how fast and how long they lasted," Davies
said.
In a third paper accepted by Icarus,
de Pater, Davies and their colleagues summarize a decade of Io observations
with the Keck II and Gemini telescopes. Their map of the surface of Io
pinpointed more than two dozen hot spots whose spatial distribution changed
significantly between 2001 and 2010. In 2010 the hot spots were dominated by
two volcanic centers: Loki Patera, an extremely large active lava lake on Io,
and Kanehekili Fluctus, an area of continuing pahoehoe lava flows.
The team hopes that monitoring Io's surface annually will reveal the style of
volcanic eruptions on the moon, constrain the composition of the magma, and
accurately map the spatial distribution of the heat flow and potential
variations over time. This information is essential to get a better
understanding of the physical processes involved in the heating and cooling
processes on Io, de Pater said.
The work is funded by the National Science Foundation and NASA's Outer Planets
Research and Planetary Geology and Geophysics Programs.
The W. M. Keck Observatory operates the
largest, most scientifically productive telescopes on Earth. The two, 10-meter
optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii
feature a suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field spectroscopy and
world-leading laser guide star adaptive optics systems.
NIRC2 (the
Near-Infrared Camera, second generation) works in combination with the Keck II
adaptive optics system to obtain very sharp images at near-infrared
wavelengths, achieving spatial resolutions comparable to or better than those
achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is
probably best known for helping to provide definitive proof of a central
massive black hole at the center of our galaxy. Astronomers also use NIRC2 to
map surface features of solar system bodies, detect planets orbiting other
stars, and study detailed morphology of distant galaxies.
Keck Observatory is a private 501(c) 3
non-profit organization and a scientific partnership of the California
Institute of Technology, the University of California and NASA.
Related Information
Media Contact:
Steve Jefferson
Communications Officer
W. M. Keck Observatory
808-881-3827
sjefferson@keck.hawaii.edu
Science Contacts:
Imke de Pater
510-643-7673
mke@berkeley.edu
Ashley Davies
818-393-1775
ashley.davies@jpl.nasa.gov
Katherine de Kleer
kdekleer@astro.berkeley.edu
