Cassini Flies Past Saturn Moon as Scientists Launch Into Data

NASA’s Cassini spacecraft made its first flyby of Saturn’s massive moon Titan on Friday, while scientists at the Jet Propulsion Laboratory in Pasadena began piecing together some of the scientific data gathered by the mission.

Their most surprising discovery was that sometime in January, “when we weren’t looking,” an unknown event released a massive amount of oxygen around the Saturnian system, according to mission team member Donald Shemansky of USC.

The findings also revealed that Saturn’s rings were almost pure ice, and that the surface of Titan apparently had many tectonic fractures caused by geologic activity.

Data from Friday’s flyby, however, was not expected to be released until today.

Scientists have been monitoring the diluted cloud of oxygen ions around Saturn throughout Cassini’s journey to the planet, but the concentration was so low that it required two-week measurements to accumulate accurate data. Measurements were often separated by a month or more.

The measurement in early February showed that the amount of oxygen had unexpectedly increased by a factor of three and, for reasons still not clear, the abundance was not symmetrical.

“The big thing is that we are seeing a massive amount of oxygen, about equal to the mass of the micron-sized particles in the E ring,” Shemansky said. The E ring is Saturn’s broad and faint outer ring.

That translates to about 1.2 billion pounds of oxygen suddenly being released from the rings. “Something is eating the ring system somehow,” he said. “The issue is, how did it happen?”

Shemansky’s best guess is that clusters of low-energy ions produced by Saturn’s magnetic field crashed into water molecules in the rings, breaking molecular bonds and scattering the oxygen into surrounding space.

Shemansky predicted that at the current rate of erosion, the E ring would disappear in 100 million years.

Before Cassini was launched, data from other missions had suggested that Saturn’s rings were about 98% ice. New data collected by Cassini’s infrared mapping spectrometer indicated the rings were more than 99% ice, said Roger Clark of the U.S. Geological Survey in Phoenix.

“Most of the rings are very, very pure ice,” he said.

Nearer to Saturn, the rings are composed primarily of small particles of ice. Farther from the planet, the particles get coarser.

The primary exceptions are in the Cassini Division and in the F ring, both of which contain relatively large amounts of what team members are calling dirt. “We haven’t identified specifically what it is,” Clark said, “but it looks remarkably like [the composition of] Phoebe.”

Phoebe is Saturn’s most distant large moon, and a flyby three weeks ago showed that it was composed of iron-containing rocks, ice and hydrocarbons. Astronomers think Phoebe is an interloper from the Kuiper Belt at the distant fringes of the solar system. The new findings suggest that the rocky material in the rings could have a similar origin.

Pictures of Titan taken before Cassini went into orbit around Saturn show an orange, fuzzy ball because the moon’s dense atmosphere is filled with organic compounds that produce a smog-like substance not penetrated by light.

By examining the moon from a distance at a variety of wavelengths, scientists were able to put together a rudimentary picture of surface features, said imaging team leader Carolyn Porco of the Space Science Institute in Boulder, Colo.

The most striking thing they have seen, she said, are crisscrossing linear features, which generally are a sign of tectonic activity, rather than impacts by asteroids.