NASA Spacecraft's Data Reveal Magma Ocean Under Jupiter Moon

Dwayne C. Brown

Headquarters, Washington

 

Jia-Rui Cook

Jet Propulsion Laboratory, Pasadena, Calif.

WASHINGTON -- New data analysis from NASA's Galileo spacecraft reveals a subsurface ocean of molten or partially molten magma beneath the surface of Jupiter's volcanic moon Io.

The finding heralds the first direct confirmation of this kind of magma layer at Io and explains why the moon is the most volcanic object known in the solar system. The research was conducted by scientists at the University of California, Los Angeles, the University of California, Santa Cruz, and the University of Michigan. The study is published this week in the journal Science.

"Scientists are excited we finally understand where Io's magma is coming from and have an explanation for some of the mysterious signatures we saw in some of the Galileo's magnetic field data," said Krishan Khurana, lead author of the study and former co-investigator on Galileo's magnetometer team at UCLA. "It turns out Io was continually giving off a 'sounding signal' in Jupiter's rotating magnetic field that matched what would be expected from molten or partially molten rocks deep beneath the surface."

Io produces about 100 times more lava each year than all the volcanoes on Earth. While Earth's volcanoes occur in localized hotspots like the "Ring of Fire" around the Pacific Ocean, Io's volcanoes are distributed all over its surface. A global magma ocean about 20 to 30 miles (30 to 50 kilometers) beneath Io's crust helps explain the moon's activity.

"It has been suggested that both the Earth and its moon may have had similar magma oceans billions of years ago at the time of their formation, but they have long since cooled," said Torrence Johnson, a former Galileo project scientist based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. He was not directly involved in the study. "Io's volcanism informs us how volcanoes work and provides a window in time to styles of volcanic activity that may have occurred on the Earth and moon during their earliest history."

NASA's Voyager spacecraft discovered Io's volcanoes in 1979, making that moon the only body in the solar system other than Earth known to have active magma volcanoes. The energy for the volcanic activity comes from the squeezing and stretching of the moon by Jupiter's gravity as Io orbits the largest planet in the solar system.

Galileo was launched in 1989 and began orbiting Jupiter in 1995. Unexplained signatures appeared in magnetic field data from Galileo flybys of Io in October 1999 and February 2000. After a successful mission, the spacecraft intentionally was sent into Jupiter's atmosphere in 2003.

"During the final phase of the Galileo mission, models of the interaction between Io and Jupiter's immense magnetic field, which bathes the moon in charged particles, were not yet sophisticated enough for us to understand what was going on in Io's interior," said Xianzhe Jia, a co-author of the study at the University of Michigan.

Recent work in mineral physics showed that a group of rocks known as "ultramafic" rocks become capable of carrying substantial electrical current when melted. Ultramafic rocks are igneous in origin, or form through the cooling of magma. On Earth, they are believed to originate from the mantle. The finding led Khurana and colleagues to test the hypothesis that the strange signature was produced by current flowing in a molten or partially molten layer of this kind of rock.

Tests showed that the signatures detected by Galileo were consistent with a rock such as lherzolite, an igneous rock rich in silicates of magnesium and iron found in Spitzbergen, Sweden. The magma ocean layer on Io appears to be more than 30 miles (50 kilometers) thick, making up at least 10 percent of the moon's mantle by volume. The blistering temperature of the magma ocean probably exceeds 2,200 degrees Fahrenheit (1,200 degrees Celsius).

The Galileo mission was managed by JPL for NASA's Science Mission Directorate in Washington. For more information about the Galileo mission and its discoveries, visit http://solarsystem.nasa.gov/galileo and http://www.jpl.nasa.gov/galileo-legacy.

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NASA Spacecraft Reveal Mysteries Of Jupiter And Saturn Rings

Dwayne C. Brown

Headquarters, Washington                              

 

Jia-Rui Cook

Jet Propulsion Laboratory, Pasadena, Calif.

 

PASADENA, Calif. -- In a celestial forensic exercise, scientists analyzing data from NASA's Cassini, Galileo and New Horizons missions have traced telltale ripples in Saturn and Jupiter's rings to specific collisions with cometary fragments that occurred decades, not millions of years, ago.

Jupiter's ripple-producing culprit was comet Shoemaker-Levy 9. The comet's debris cloud hurtled through the thin Jupiter ring system on a collision course into the planet in July 1994. Scientists attribute Saturn's ripples to a similar object - likely another cloud of comet debris - plunging through the inner rings in 1983. The findings are detailed in two papers published Thursday in the journal Science.

"We're finding evidence that a planet's rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago," said Matthew Hedman, a Cassini imaging team associate, lead author on one of the papers, and a research associate at Cornell University in Ithaca, N.Y. "The solar system is a much more dynamic place than we gave it credit for."

Scientists learned about the patchy patterns in Jupiter's rings in the late 1990s from Galileo's visit to Jupiter. Unfortunately, the images from that mission were fuzzy, and scientists didn't understand why such patterns would occur. Not until Cassini entered orbit around Saturn in 2004 and started sending back thousands of images did scientists have a better picture of the activity. A 2007 science paper by Hedman and colleagues first noted corrugations in Saturn's innermost ring, dubbed the D ring.

A group including Hedman and Mark Showalter, a Cassini co-investigator based at the SETI Institute in Mountain View, Calif., saw that the grooves in the D ring appeared to wind together more tightly over time. Playing the process backward, Hedman demonstrated the pattern originated when something tilted the D ring off its axis by about 300 feet (100 meters) in late 1983. The scientists found Saturn's gravity on the tilted area warped the ring into a tightening spiral.

Cassini imaging scientists received another clue around August 2009 when the sun shone directly along Saturn's equator and lit the rings edge-on. The unique lighting conditions highlighted ripples not previously seen in another part of the ring system. Whatever happened in 1983 was big - not a small, localized event.

The collision tilted a region more than 12,000 miles (19,000 kilometers) wide, covering part of the D ring and the next outermost ring, called the C ring. Unfortunately, spacecraft were not visiting Saturn at that time, and the planet was on the far side of the sun out of sight from ground or space-based telescopes.

Hedman and Showalter, the lead author on the second paper, wondered whether the long-forgotten pattern in Jupiter's ring system might illuminate the mystery. Using Galileo images from 1996 and 2000, Showalter confirmed a similar winding spiral pattern by applying the same math they had applied to Saturn and factoring in Jupiter's gravitational influence. Galileo was launched on a space shuttle in 1989 and studied Jupiter until 2003.

Unwinding the spiral pinpointed the date when Jupiter's ring was tilted off its axis between June and September 1994. Shoemaker-Levy plunged into the Jovian atmosphere in late July. The Galileo images also revealed a second spiral, which was calculated to have originated in 1990. Images taken by New Horizons in 2007, when the spacecraft flew by Jupiter on its way to Pluto, showed two newer ripple patterns, in addition to the fading echo of the Shoemaker-Levy impact.

"We now know that collisions into the rings are very common – a few times per decade for Jupiter and a few times per century for Saturn," Showalter said. "Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later."

Launched in Oct. 15, 1997, Cassini began orbiting Saturn in 2004 and sends back data daily.

"Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system," said Linda Spilker, Cassini project scientist, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Cassini's long sojourn around Saturn has helped us tease out subtle clues that tell us about the history of our origins."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate in Washington. The imaging team is based at the Space Science Institute in Boulder, Colo. For more information about Cassini, visit http://www.nasa.gov/cassini.

Pluto New Horizons launched in 2006 on the first mission to study Pluto and the Kuiper Belt. The mission is managed by the Johns Hopkins Applied Physics Laboratory in Laurel, Md., for NASA. The mission is part of the New Frontiers program managed at the agency's Marshall Space Flight Center in Huntsville, Ala. For more information about Pluto New Horizons, visit http://www.nasa.gov/newhorizons.

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