By Mary O’KEEFE

Galileo was the first to observe Saturn with a telescope in 1610 and was confused by it. Saturn, from a telescope, looks flat and there were, of course, those amazing rings. It was not until 1659 that Christian Huygens inferred the geometry of the rings and for centuries Saturn appeared to be unique. But then rings were discovered around Uranus, Jupiter and Neptune. Although Saturn lost its one-of-a-kind ring dominance it has remained of great curiosity to the scientific world.

In 1979, Pioneer 11 was the first spacecraft to visit Saturn followed by Voyager 1 and Voyager 2 in the 1980s. Astronomers have continued to view the planet from our own “Blue Dot,” but then came Cassini Huygens that arrived at Saturn on July 1, 2004.

The ambitious Cassini mission, managed by Jet Propulsion Laboratory, was to explore Saturn, its rings and moons. It carried with it a passenger – Huygens, a probe that parachuted to the surface of Titan, Saturn’s largest moon.

As with most JPL-managed missions, it went beyond its planned mission time of four years and is about to come to an end.

“We are in the grand finale phase of [Cassini], 22 orbits where we, for 22 times, will pass through the narrow gap of the outer most of Saturn’s atmosphere to inside Saturn’s rings,” said Jo Eliza Pitesky, PhD, JPL Cassini project science systems engineer, technical group supervisor, science system engineering.

Like dolphins playing in the surf, breaching and diving, Cassini will dive into the top layer of the planet’s atmosphere, then fly back up to the rings. This will happen 22 times.

When asked if engineers were concerned about this new part of the mission, she joked, “The job of engineers is to be concerned all the time.”

During this part of the mission Cassini will not go into the rings but into the gap, a narrow region, Pitesky said.

At the beginning of this part of the mission engineers made a pass in that region between Saturn and its rings. The spacecraft was turned so that its 13-foot wide antenna pointed in the direction of oncoming ring particles thus shielding the more delicate instruments.

“Like a cow catcher, although there are no cows,” Pitesky said. “And we are going 77,000 miles per hour.”

What astounded engineers and scientists was they found there was very little dust. The Radio and Plasma Wave Science (RPWS) instrument was one of the scientific instruments that used its sensors to record the dust particles.

RPWS detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside Saturn’s main rings, according to a JPL statement. But inside the narrow gap between atmosphere and inner-most ring, they only detected a few hits.

“One of the scientists said there are more people sitting around this table than dust particles,” Pitesky said of a recent meeting.

The first of the tests have already revealed so much, including the “eye of the hurricane.”

“There is some stuff I have never seen before,” she added. “The planet is still surprising.”

Cassini will continue playing in the cosmic surf until the last dive. Between dives 22 and 23 Cassini will make a final encounter with Titan. The weekly dives began in April and will end in September of this year. Its last dive will be bittersweet for Pitesky and those who are working on the Cassini project.

Pitesky has been at JPL for over 30 years and was part of Cassini project for 16 of those years. When she was in college she came to the lab and toured with her friend Fred Scarf, who developed the acoustic recording project for Voyager, and was the principal investigator for that mission’s Plasma Waves.

“Fred [spoke of] this really far out idea of this spacecraft going to Saturn,” she recalled. That mission sounded amazing and she fell in love with JPL.

“This was the place I wanted to work when I grew up,” she said. “It is a privilege to do this work.”

She was hired at JPL and then became part of the Cassini project. Scarf has since passed away.

“I am helping to end the mission he began,” she said.

Between the 22nd and 23rd dives Cassini will make its final descent.

“We say that is when Isaac Newton is in the driver’s seat,” she said. “Cassini will go out in a blaze of glory and will be doing science all the way to the end.”

The information gathered will give insight to how Earth was formed. The data collected from Cassini will continue to be studied, and will continue to raise questions for scientists and engineers as it has for centuries. All are listening until the final dive.

“And then Cassini will go silent.”

To follow Cassini: The Grand Finale visit http://saturn.jpl.nasa.gov.

  Mary Okeefe