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Revelations in Saturn’s Rings Continue as Equinox Approaches

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(Above) The Cassini spacecraft captured this image of a small object in the outer portion of Saturn’s B ring casting a shadow on the rings as Saturn approaches its August 2009 equinox.

Thanks to a special play of sunlight and shadow as Saturn continues its march towards its August 11 equinox, recent images captured by NASA’s Cassini spacecraft are revealing new three-dimensional objects and structures in the planet’s otherwise flat rings. The Cassini spacecraft captured this image of a small object in the outer portion of Saturn’s B ring casting a shadow on the rings as Saturn approaches its August 2009 equinox.

This new moonlet, situated about 300 miles (480 kilometers), inward from the outer edge of the B ring, was found by detection of its shadow which stretches 25 miles, or 41 kilometers, across the rings. The shadow length implies the moonlet is protruding about 660 feet, or 200 meters, above the ring plane. If the moonlet is orbiting in the same plane as the ring material surrounding it, which is likely, it must be about 1,300 feet, or 400 meters, across. This object is not attended by a propeller feature, unlike the band of moonlets discovered in Saturn’s A ring earlier by Cassini. The A ring moonlets, which have not been directly imaged, were found because of the propeller-like narrow gaps on either side of them that they create as they orbit within the rings. The lack of a propeller feature surrounding the new moonlet is likely because the B ring is dense, and the ring material in a dense ring would be expected to fill in any gaps around the moonlet more quickly than in a less dense region like the mid-A ring. Also, it may simply be harder in the first place for a moonlet to create propeller-like gaps in a dense ring.

The search for three-dimensional structures in Saturn’s rings has been a major goal of the imaging team during Cassini’s “Equinox Mission,” the two-year period containing exact equinox — that moment when the sun is seen directly overhead at noon at the planet’s equator. This novel illumination geometry, which occurs every half-Saturn-year, or about 15 Earth years, lowers the sun’s angle to the ring plane and causes out-of-plane structures to cast long shadows across the rings’ broad expanse, making them easy to detect.

Posted
August 8th, 2009

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Tiny Saturn Moon Could Be Targeted in Search for ET Life

(Above) Cassini imaging scientists used views like this one to help them identify the source locations for individual jets spurting ice particles, water vapor and trace organic compounds from the surface of Saturn’s moon Enceladus.

Plumes spewing from a tiny moon of Saturn – a moon roughly the width of Arizona – are filled with molecules that suggest that the moon, Enceladus, is likely another place in the solar system to look for life, Cassini scientist Jonathan Lunine of The University of Arizona Lunar and Planetary Laboratory said.

When NASA’s Cassini spacecraft flew through a plume erupting from Enceladus early last October, its Ion and Neutral Mass Spectrometer instrument measured ammonia, argon 40 and an abundance of carbon-bearing molecules, or “organics,” entrained in the water vapor.

Lunine is on the team reporting the results in the July 23 issue of the journal Nature.

Cassini discovered water vapor and particles spewing from Enceladus in a previous, more distant flyby in 2005. Since then, scientists have been trying to determine if the source of the jets is liquid.

“The fact that there’s ammonia on Enceladus is important because it argues the plumes are erupting from a region of liquid water beneath the surface of Enceladus, rather than erupting from what is just warm ice,” Lunine said.

Ammonia acts as antifreeze. Water containing ammonia remains liquid at temperatures as low as minus 143 degrees Fahrenheit.

Cassini has measured temperatures higher than minus 136 degrees Fahrenheit near the fractures where Enceladus shoots out its water vapor plumes, so “We think we have an excellent argument for a liquid water interior,” said Hunter Waite of the Southwest Research Institute in San Antonio, Texas, lead scientist for Cassini’s Ion and Neutral Mass Spectrometer experiment.

Argon 40, an isotope of argon, which is a decay product of potassium, also strengthens the argument for a liquid water source, Lunine said. Rocks on Earth and elsewhere, including Saturn’s giant moon Titan, give off argon 40.

“The fact that we found a lot of argon 40 also argues for liquid water,” Lunine said. Liquid water most likely circulating through Enceladus’ rocky core is the best explanation for all the argon 40 detected, he said.

The Cassini team also discovered such carbon-bearing molecules as methane, formaldehyde, ethanol and hydrocarbons are plentiful in the plumes.

Given other recently reported Cassini evidence for sodium and potassium in Saturn’s E ring – a ring made of material that comes from Enceladus, there must be a salty, liquid layer in Enceladus that “seems like a pretty good environment for life,” Lunine said.

“What I think is really interesting now is that we have four places in the outer solar system with interior oceans,” he said.

Scientists have evidence that Saturn’s Titan and Jupiter’s moons Europa and Ganymede also have oceans.

Mars, Titan, Europa and now Enceladus seem to be good sites to search for extraterrestrial life, Lunine added.

Posted
July 26th, 2009

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Saturnian Moon Shows Evidence of Ammonia

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(Above) Saturn’s moon Enceladus, seen by the Cassini spacecraft.

Data collected during two close flybys of Saturn’s moon Enceladus by NASA’s Cassini spacecraft add more fuel to the fire about the Saturnian ice world containing sub-surface liquid water. The data collected by Cassini’s Ion and Neutral Mass Spectrometer during Enceladus flybys in July and Oct. 2008, were released in the July 23 issue of the journal Nature.

“When Cassini flew through the plume erupting from Enceladus on October 8 of last year, our spectrometer was able to sniff out many complex chemicals, including organic ones, in the vapor and icy particles,” said Hunter Waite, the Cassini Ion and Neutral Mass Spectrometer Lead Scientist from the Southwest Research Institute in San Antonio, Texas. “One of the chemicals definitively identified was ammonia.”

On Earth, the presence of ammonia means the potential for sparkling clean floors and counter tops. In space, the presence of ammonia provides strong evidence for the existence of at least some liquid water.

How could ammonia equate to liquid water inside an ice-covered moon in one of the chillier neighborhoods of our solar system? As many a homeowner interested in keeping their abodes spick and span know, ammonia promptly dissolves in water. But what many people do not realize is that ammonia acts as antifreeze, keeping water liquid at lower temperatures than would otherwise be possible. With the presence of ammonia, water can exist in a liquid state to temperatures as low as 176 degrees Kelvin (-143 degrees Fahrenheit).

“Given that temperatures in excess of 180 Kelvin (-136 degrees Fahrenheit) have been measured near the fractures on Enceladus where the jets emanate, we think we have an excellent argument for a liquid water interior,” said Waite.

Cassini discovered water vapor and particles spewing from Enceladus in 2005. Since then, scientists have been trying to determine if the plume originates from a liquid source inside the moon or is due to other causes.

“Ammonia is sort of a holy grail for icy volcanism,” said William McKinnon, a scientist from Washington University in Saint Louis, Missouri. “This is the first time we’ve found it for sure on an icy satellite of a giant planet. It is probably everywhere in the Saturn system.”

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(Above) The Cassini spacecraft orbits Saturn.

Just how much water is contained within Enceladus’ icy interior is still up for debate. So far, Cassini has made five flybys of Enceladus, one of the chief targets for Cassini’s extended mission. Two close flybys are scheduled for November of this year, and two more close flybys are scheduled for April and May or 2010. Data collected during these future flybys may help settle the debate.

“Where liquid water and organics exist, is there life?” asked Jonathan Lunine a Cassini scientist from the University of Arizona, Tucson. “Such is the case for Earth; what was found on Enceladus bolsters this moon’s promise for containing potential habitable environments.”

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

Posted
July 23rd, 2009

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