Pasadena takes center stage Friday, Sept. 15, as a nearly 20-year journey to Saturn, the mysterious ringed, gaseous jewel of our solar system, comes to a spectacular, flaming end.
The unmanned spacecraft once known as Cassini-Huygens, now simply Cassini, is set to become a fireball early Friday morning as it enters Saturn’s atmosphere, ending a trip that began for many scientists well before the spacecraft’s Oct. 15, 1997 launch.
The public can watch Cassini’s final moments live on NASA TV and online, beginning Thursday night.
“The mission has been insanely, wildly, beautifully successful,” Curt Niebur, Cassini program scientist at NASA Headquarters in Washington, DC, gushed during a recent media teleconference. That’s because scientists have been able to “pursue questions that we never thought Cassini would have the opportunity to answer,” he said.
Earl Maize, Cassini project manager at JPL, may have been the by-the-numbers guy in the presentation, but he also waxed poetic after stating that some 635 gigabytes of collected scientific data became part of nearly 4,000 scientific papers. Of Cassini’s 162 targeted flybys of Saturn’s 53 named and nine unnamed moons, 127 were of Titan. What he called Cassini’s “long-term relationship with Titan” ended with a Sept. 11 flyby during which Titan deflected Cassini into an impact trajectory, “like a final kiss goodbye with Titan,” Maize said.
JPL Cassini Project Scientist Linda Spilker compared Cassini’s grand finale to “a last look around your house or apartment just before you move out,” when “memories across the years come flooding back.” Saturn has been Cassini’s home for the last 13 years.
The fourth space probe to visit the solar system’s second-largest planet (preceded by Voyager 1, Voyager 2 and Pioneer 11), Cassini is the first to orbit the gaseous giant. Cassini-Huygens was actually two things initially: an orbiter (Cassini) and a lander (Huygens). Named after the 17th-century Dutch astronomer who discovered Titan, Christiaan Huygens, Huygens was a project of the European Space Agency (ESA) which landed on Titan on Jan. 14, 2005, sending data back to Earth for 90 minutes. Titan is Saturn’s largest moon and is now the only known place in space outside of our own planet that collects water on the surface.
The orbiter was named after the Italian-born naturalized French astronomer Giovanni Domenico Cassini who discovered four of Saturn’s moons and a division in the planet’s distinctive rings.
Originally, the Cassini mission was only a four-year tour, which was completed in 2008, but resulted in two extensions. During its time, Cassini discovered six new moons as well as new rings. The Cassini-Huygens mission also brought together three agencies (NASA, the European Space Agency and the Italian space agency), with a total of 27 nations participating. But JPL designed, developed and assembled the Cassini orbiter.
Niebur and Spilker were quick to remind how different technology was in the 1990s. Neibur noted that cellphones were “the size of a brick” and cost about $5,000 in today’s money. Spilker recalled that when she began working on Cassini, “I gave most of my presentation using an overhead projector and viewgraphs.”
If you want a visual update that includes experts from JPL, PBS NOVA featured a one-hour episode on Cassini, “Death Dive to Saturn” on Wednesday, Sept, 13, which is currently available to stream. “Death Dive to Saturn” joins last month’s NOVA episode on the total eclipse, “Eclipse Across America,” and the PBS presentation of the independent documentary on another space probe, “The Farthest — Voyager in Space” (streaming online Sept. 14-27). If you watched the Voyager movie, you’ll recognize some faces in the NOVA special on Saturn, such as Carolyn Porco, principal investigator of the project’s imaging science subsystem.
Spilker, who joined the Voyager mission in 1977 and began on Cassini in 1988, is also prominently featured on “Death Dive to Saturn,” but her memories are more personal. The documentary shows a grainy photo of a young Spilker who recalls, “When I first started working on Cassini, my daughter, Jennifer, had just started kindergarten and now she’s married with a daughter of her own.”
“Death Dive to Saturn” puts things in perspective. While Voyager was 1970s technology, Cassini is ’90s technology. That means the memory on Cassini is less than we have on our smartphones. Still, the 5,000-pound Cassini, dubbed Battlestar Galactica by another expert on the documentary for all the scientific instruments it contains, also added to our knowledge of Saturn’s many moons, which range in size from larger than the planet Mercury to the size of a sports arena.
Their shape also varies. Some are spherical, much like our own moon, including Mimas, which, with its large Herschel Crater, resembles the Death Star from “Star Wars.” Others have been described in terms of food. Prometheus, for instance, is shaped like a sweet potato, Pandora looks like a regular potato, Janus looks like a meatball. Inside one of the rings is something unofficially called Peggy, which may be a moon that is either forming or disintegrating.
Cassini also found liquid on the south polar region of Saturn’s moon Enceladus. Scientists believe Enceladus’ subsurface ocean has all the ingredients necessary for life: liquid water, heat and methane. Cassini also found that the moon Hyperion has a statically charged surface. Saturn’s many moons contribute material to Saturn’s rings and magnetosphere, but these same moons also collect material that forms the rings and magnetosphere.
Since April, Cassini had been making daring dives through the 1,200-mile-wide gap between Saturn and its rings. The small craft skimmed the outer edges of the planet’s atmosphere and the inner edges of the rings, sending back amazing photographs. In its final five orbits, it will have passed through Saturn’s uppermost atmosphere before making the final plunge directly into the gaseous planet’s surface for a fiery end.
If you’re wondering why Voyager was allowed to continue on and Cassini is taking a death dive, the explanation is simple. Scientists were worried that Cassini might collide with one of those many moons and contaminate any future studies of habitability and potential life.
During the dive there is also a concern that Cassini might impact with ring material — space stuff the size of a grain-of-sand that could damage an instrument or the entire spacecraft. Yet this strategy, if successful, will provide unprecedented opportunities for scientists to measure Saturn’s atmospheric composition and interior structure. This way, Cassini will be able to measure gravity and magnetic fields, evaluate the total main-ring mass to estimate the system’s age and longevity, and sample Saturn’s ring particles, innermost radiation belts and upper atmosphere before burning up.
On Thursday, Cassini’s cameras will transmit the last images of the moons Titan and Enceladus, as well as Saturn’s rings. JPL will be hosting a private Cassini NASA Social which will be live streamed on YouTube, Ustream and NASA TV. The final plunge begins at about 1:37 a.m. Friday. Mission Control will be live on YouTube, Ustream and NASA TV. By about 5 a.m. Cassini will break up like a meteor, ending its mission. Check NASA’s Live Streaming Channel Guide at saturn.JPL.NASA.gov/mission/grand-finale/for-media.
“In Cassini’s final orbit, plunging into Saturn’s atmosphere, sending back science until the very last second … we’ll continue to learn from Cassini long after the end of the mission,” said Spilker.