NASA's Hubble Observations Suggest Underground Ocean on Jupiter's Largest Moon

Artist's Concept of Aurorae and Ganymede

Illustration Credit: NASA, ESA, and G. Bacon (STScI) 

Science Credit: NASA, ESA, and J. Saur (University of Cologne, Germany)

Release Images

Ganymede Interior

This is an illustration of the interior of Jupiter's largest moon, Ganymede. It is based on theoretical models, in-situ observations by NASA's Galileo orbiter, and Hubble Space Telescope observations of the moon's aurorae, which allows for a probe of the moon's interior. The cake-layering of the moon shows that ices and a saline ocean dominate the outer layers. A denser rock mantle lies deeper in the moon, and finally an iron core beneath that. Credit: NASA, ESA, and A. Feild (STScI)


NASA's Hubble Space Telescope has the best evidence yet for an underground saltwater ocean on Ganymede, Jupiter's largest moon. The subterranean ocean is thought to have more water than all the water on Earth's surface.

Identifying liquid water is crucial in the search for habitable worlds beyond Earth and for the search for life as we know it.

"This discovery marks a significant milestone, highlighting what only Hubble can accomplish," said John Grunsfeld, assistant administrator of NASA's Science Mission Directorate at NASA Headquarters, Washington, D.C. "In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth."

Ganymede is the largest moon in our solar system and the only moon with its own magnetic field. The magnetic field causes aurorae, which are ribbons of glowing, hot electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, it is also embedded in Jupiter's magnetic field. When Jupiter's magnetic field changes, the aurorae on Ganymede also change, "rocking" back and forth.

By watching the rocking motion of the two aurorae, scientists were able to determine that a large amount of saltwater exists beneath Ganymede's crust, affecting its magnetic field.

A team of scientists led by Joachim Saur of the University of Cologne in Germany came up with the idea of using Hubble to learn more about the inside of the moon.

"I was always brainstorming how we could use a telescope in other ways," said Saur. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon's interior."

If a saltwater ocean were present, Jupiter's magnetic field would create a secondary magnetic field in the ocean that would counter Jupiter's field. This "magnetic friction" would suppress the rocking of the aurorae. This ocean fights Jupiter's magnetic field so strongly that it reduces the rocking of the aurorae to 2 degrees, instead of 6 degrees if the ocean were not present.

Scientists estimate the ocean is 60 miles (100 kilometers) thick — 10 times deeper than Earth's oceans — and is buried under a 95-mile (150-kilometer) crust of mostly ice.

Scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon. NASA's Galileo mission measured Ganymede's magnetic field in 2002, providing the first evidence supporting those suspicions. The Galileo spacecraft took brief "snapshot" measurements of the magnetic field in 20-minute intervals, but its observations were too brief to distinctly catch the cyclical rocking of the ocean's secondary magnetic field.

The new observations were done in ultraviolet light and could only be accomplished with a space telescope high above Earth's atmosphere, which blocks most ultraviolet light.

The team’s results will be published online in the Journal of Geophysical Research: Space Physics on March 12.

NASA's Hubble Space Telescope is celebrating 25 years of groundbreaking science on April 24. It has transformed our understanding of our solar system and beyond, and helped us find our place among the stars. To join the conversation about 25 years of Hubble discoveries, use the hashtag #Hubble25.

Contact

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov

Joachim Saur
University of Cologne, Cologne, Germany
jsaur@uni-koein.de

Source: HubbleSite

  

Observations Reveal Massive Eruptions on Jupiter’s Moon Io

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

• Two new, rare, high-effusion outburst eruptions at Rarog and Heno Paterae on Io

• Near-infrared monitoring of Io and detection of a violent outburst on 29 August 2013

• Global near-IR maps from Gemini-N and Keck Observatory in 2010, with a special focus on Janus Patera and Kanehekili Fluctus

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

Source: W. M. Keck Observatory

Adaptive Optics allows Earth-based monitoring of Io’s Fiery show

Quiescent activity of Io observed in 2010 and 2011 showing several quasi-permanent eruptions at 3.8 microns [bottom] and the absence of bright, hotter outbursts at 2.1 microns. 

Kamuela, Hawaii – Watching active volcanic eruptions should be done from a safe distance, and a group of California researchers has figured out how to do it from, ironically, Mauna Kea – one of Earth’s tallest volcanoes – using the W. M. Keck Observatory. Employing an ingenious combination of telescopic surveys and archival data, they have gathered nearly 40 distinct snapshots of effusive (slow) volcanic eruptions and high temperature outbursts on Jupiter’s tiny moon, Io, showing details as small as 100 km (60 miles) on the moon’s surface. 

While space-based telescopes were once required for viewing surface details on Io – similar in size to our Moon, but more than 1,600 times distant – adaptive optics (AO), pioneered at Keck, allows teams like that led by Franck Marchis, a researcher at the Carl Sagan Center of the SETI Institute, to collect fascinating data on the wild show from Earth. Marchis presented results from ground-based telescopic monitoring of Io’s volcanic activity over the past decade this week, at the 2012 Division of Planetary Sciences Meeting of the American Astronomical Society.

Erupting volcanoes on Io cannot be seen well from beneath the Earth’s atmosphere using classical astronomical techniques. Io is a relatively small satellite with a 3,600 km diameter, more than 630 million kilometers away. In 1979, Voyager 1 visited the Jovian system, revealing Io’s dynamic volcanic activity from the first close-up pictures of its surface, capturing bizarre volcanic terrains, active plumes and hot spots. The Galileo spacecraft remained in orbit in the Jovian system from 1995 to 2003 and observed more than 160 active volcanoes and a broad range of eruption styles. Several outstanding questions remained in the post-Galileo era, and the origin and long-term evolution of Io’s volcanic activity is still not fully understood. 

In the meantime, astronomers designed instruments to break the “seeing barrier” and improve the image quality of ground-based telescopes. The blurring (“seeing”) introduced by the constant motion of the Earth’s atmosphere can be measured and corrected in real time using adaptive optics (AO), providing an image with a resolution close to the theoretical “diffraction limit” of the telescope. The W. M. Keck Observatory has used adaptive optics since 1999. 

“Since our first observation of Io in 2001 using the Keck II 10-meter telescope and its AO system from Mauna Kea in Hawaii, our group became very excited about the technology.  We also began using AO at the Very Large Telescope in Chile, and at the Gemini North telescope in Hawaii.  The technology has improved over the years, and the image quality and usefulness of these AO systems have made them part of the essential instrument suite for large telescopes,” said Marchis.

Since 2003, combining their own observing programs with archival data, the team led by Marchis has gathered approximately 40 epochs of observations of Io in the near-infrared. These images show details as small as 100 km (60 miles) on the surface of the satellite. 

Their observations have revealed young and energetic eruptions called outbursts.  These are easily detectable from their immense thermal emission at shorter wavelengths, implying a high eruption temperature. The team observed the awakening of the volcano Tvashtar simultaneously with the New Horizons spacecraft, which flew past Jupiter on its way to Pluto. From a combined survey based on three large telescopes, they reported that the eruption was detectable from April 2006 to September 2007. Older observations from the Galileo spacecraft and the W. M. Keck Observatory show that this volcano previously displayed a similar “fire fountain” eruption which started in November 1999 and lasted for 15 months. Similarly, Pillan, an energetic eruption detected with the Galileo spacecraft from 1996 to 1999, had sporadic activity again in August 2007 that was reported by the team using the Keck II telescope.

“The episodicity of these volcanoes points to a regular recharge of magma storage chambers” said Ashley Davies a volcanologist at the Jet Propulsion Laboratory, California Institute of Technology, and a member of the study.  “This will allow us to model the eruption process and understand how heat is removed from Io’s deep interior by this particular style of volcanic activity.”

Four additional young eruptions were detected during this survey including an extremely active volcano located at a region that had never shown activity in the past. The new activity was seen in May 2004 and had a total output of 10% the average Io thermal output. This was more energetic than Tvashtar in 2001, implying a fire fountain style eruption. Interestingly, the team did not observe any “mega-outburst” during this survey, with an energetic output similar to the eruption on Surt in 2001, the most energetic eruption ever witnessed in the Solar System. They conclude that such outbursts are rare and short-lived, typically lasting only a few days.

The team and several others groups continued to monitor Io’s volcanic activity. They noticed that since September 2010, Io’s volcanic activity has been globally quiescent. A dozen permanent, low temperature eruptions, which represent less dramatic “effusive” activity, are still detected across the surface of Io, but recent observations of the satellite show an absence of young bright eruptions.

“Spacecraft have only been able to capture fleeting glimpses of Io’s volcanoes, Voyager for a few months, Galileo a few years, and New Horizons a few days.  Ground-based observations, on the other hand, can continue to monitor Io’s volcanoes over long time-scales. The more telescopes looking at Io, the better time coverage we can obtain,” said Julie Rathbun from Redlands University, a planetary scientist not directly involved in this study but who has monitored Io for more than 15 years.. “AO observations from 8- to 10-meter class telescopes are a dramatic improvement in spatial resolution over previous ground-based observations.  Soon they will not only be our only way to monitor Io’s volcanoes, but the best way.  We should be making these observations more often.”

The monitoring of Io’s volcanism will continue to build a timeline of activity and thermal emission variability, which will be further complemented by data obtained by other missions to the Jupiter system (such as the ESA mission JUICE, or a future dedicated Europa or Io mission). Until these missions, however, the large, AO-enabled ground-based telescopes will shoulder the task of monitoring Io’s volcanic activity.

The next generation of AO systems will provide even better image quality and open the visible wavelength range to planetary astronomers. These systems are currently under development and will have their first light in the coming years. Colorful surface changes due to volcanic activity, such as plume deposits or lava flow fields, will be detectable from the ground.

 “The understanding and characterization of volcanoes on Io is one of the many very exciting applications of the current Keck AO systems,” said Peter Wizinowich, Optical Systems Manager at W. M Keck Observatory. “Marchis’ simulations of what Keck’s proposed Next Generation AO system (NGAO) could do for the field of solar system astronomy remind us that there is a lot more breakthrough science awaiting the delivery of NGAO.” 

The W. M. Keck Observatory operates two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system. The 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.