NASA's Cassini Discovers Potential Liquid Water on Enceladus

March 9, 2006
(Source: NASA/JPL)

Enceladus the Storyteller:
NASA's Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn's moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

"We realize that this is a radical conclusion -- that we may have evidence for liquid water within a body so small and so cold," said Dr. Carolyn Porco, Cassini imaging team leader at Space Science Institute, Boulder, Colo. "However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms."

High-resolution Cassini images show icy jets and towering plumes ejecting large quantities of particles at high speed. Scientists examined several models to explain the process. They ruled out the idea that the particles are produced by or blown off the moon's surface by vapor created when warm water ice converts to a gas. Instead, scientists have found evidence for a much more exciting possibility -- the jets might be erupting from near-surface pockets of liquid water above 0 degrees Celsius (32 degrees Fahrenheit), like cold versions of the Old Faithful geyser in Yellowstone.


Spray Above Enceladus III
Mission scientists report these and other Enceladus findings in this week's issue of Science.

"We previously knew of at most three places where active volcanism exists: Jupiter's moon Io, Earth, and possibly Neptune's moon Triton. Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system," said Dr. John Spencer, Cassini scientist, Southwest Research Institute, Boulder, Colo.

"Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust," said Dr. Andrew Ingersoll, imaging team member and atmospheric scientist at the California Institute of Technology, Pasadena, Calif. "What's different here is that pockets of liquid water may be no more than tens of meters below the surface."

Other unexplained oddities now make sense. "As Cassini approached Saturn, we discovered that the Saturnian system is filled with oxygen atoms. At the time we had no idea where the oxygen was coming from," said Dr. Candy Hansen, Cassini scientist at NASA's Jet Propulsion Laboratory in Pasadena. "Now we know that Enceladus is spewing out water molecules, which break down into oxygen and hydrogen."


Enceladus "Cold Geyser" Model
Scientists are also seeing variability at Enceladus. "Even when Cassini is not flying close to Enceladus, we can detect that the plume's activity has been changing through its varying effects on the soup of electrically-charged particles that flow past the moon," said Dr. Geraint H. Jones, Cassini scientist, magnetospheric imaging instrument, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

Scientists still have many questions. Why is Enceladus currently so active? Are other sites on Enceladus active? Might this activity have been continuous enough over the moon's history for life to have had a chance to take hold in the moon's interior?

"Our search for liquid water has taken a new turn. The type of evidence for liquid water on Enceladus is very different from what we've seen at Jupiter's moon Europa. On Europa the evidence from surface geological features points to an internal ocean. On Enceladus the evidence is direct observation of water vapor venting from sources close to the surface," said Dr. Peter Thomas, Cassini imaging scientist, Cornell University, Ithaca, N.Y.

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles), but much work remains after Cassini¿s four-year prime mission is over.


Searching for Warmth
"There's no question that, along with the moon Titan, Enceladus should be a very high priority for us. Saturn has given us two exciting worlds to explore," said Dr. Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona, Tucson, Ariz.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the Caltech, manages the mission for NASA's Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and more information, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Contacts:
Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Erica Hupp/Dolores Beasley (202) 358-1237/1726
NASA Headquarters, Washington

NEWS RELEASE: 2006-033

Scientists Solve the Mystery of Methane in Titan's Atmosphere
March 1, 2006
(Source: University of Arizona, Tucson)

By Lori Stiles

An international team of planetary scientists may have solved the mystery of why the atmosphere of Saturn's moon, Titan, is rich in methane.

Methane, which on Titan plays a role similar to water on Earth, is locked in a methane-rich water ice that forms a crust above an ocean of liquid water mixed with ammonia, the scientists say. Major episodes of outgassing pumped methane into Titan's mostly nitrogen atmosphere three times during the moon's evolutionary history, they discovered.

Gabriel Tobie of the University of Nantes, France, Jonathan Lunine of The University of Arizona and Christophe Sotin, also of the University of Nantes, describe their model of how Titan's atmosphere evolved in the March 2 issue of Nature. (Lunine is currently on sabbatical at the Italian National Astrophysics Institute in Rome, Italy.)

Results from the European Space Agency's Huygens probe that landed on Titan Jan. 14, 2005, and remote sensing instruments on NASA's Cassini orbiter agree with their findings, they add.

The presence of methane in Titan's atmosphere is one of the major enigmas that the Cassini-Huygens mission to Saturn's system is trying to resolve, they noted.

Scientists have long known that Titan's atmosphere contains methane, ethane, acetylene and many other hydrocarbon compounds. But sunlight irreversibly destroys methane after tens of millions of years, so something has replenished methane in Titan's thick air during the moon's 4.5 billion-year history.

The first episode of methane gas release happened after Titan formed its dense rock core and water mantle beneath an ice crust, said UA planetary sciences Professor Jonathan Lunine, an interdisciplinary scientist for the Huygens probe.

Ammonia acting as an antifreeze, heat leftover from formation, and heat from radioactive elements aided the release of methane during the first billion years, or possibly just a few hundred million years, in Titan's history. Much of the methane in this first release might have been reabsorbed into Titan's interior. But whatever methane was left in the atmosphere was photochemically destroyed in the first billion years, Lunine said.

The second methane-release episode around two billion years ago is even more interesting, Lunine said. That's when convection began within Titan's silicate core.

"The core, made of rock, continued to heat up because it contains natural radioactive elements like uranium, potassium and thorium. On Earth, these elements are concentrated in the crust, but on Titan, they'd be deep down in the rock. So the core gets hotter and hotter, until finally it's soft enough for convection to start."

Convection is the mechanical turnover of material to remove heat. The second event of around two billion years ago injected a burst of convection heat into Titan's overlying mantle, causing the ice crust to thin and methane to outgas through ice to the surface.

The latest methane-release episode began around 500 million years ago. It's the result of the planet cooling by convection in Titan's solid ice crust.

While the cause for each outgassing episode differs, the result is the same, Lunine said: "There's an injection of methane into the surface and atmosphere of Titan. We are now in an era where there's enough outgassing to add methane to the atmosphere, but not enough for widespread seas of methane."

This outgassing episode will be Titan's last. "There'll be no further such events until billions of years in the future, when the sun goes red giant and cooks Titan," Lunine said. "Methane outgassing will cease within the next few hundred million years. Then photochemistry will destroy the surface methane and Titan will indeed dry up. The atmosphere will clear of haze, and Titan will look very different."

When the Huygens probe warmed Titan's damp surface where it landed in January 2005, its instruments inhaled whiffs of methane. The heat of the probe caused methane trapped in pores just below the surface to evaporate, just as subsurface water would evaporate on Earth if you fired up a camping stove in the sand of a dry streambed.

The UA-led Descent Imager Spectral Radiometer experiment, which was the Huygens camera, revealed Titan's spectacular landscapes apparently carved by liquid methane.

Contacts:
Contact Information
Gabriel Tobie
University of Nantes, France
+33 1-5112-5467
gabriel.tobie@univ-nantes.fr

Jonathan Lunine
University of Arizona
+39 06-4993-4052
jlunine@lpl.arizona.edu

Christophe.Sotin
University of Nantes, France
+33 1-5112-5466
christophe.sotin@univ-nantes.fr