The Cassini spacecraft Friday plunged into Saturn’s atmosphere at around 70,000 miles per hour and vaporized in the dramatic conclusion of a 20-year mission through space, including 13 years circling the ringed planet.
“The Cassini spacecraft … transmitted its final signals from Saturn, and then became a part of the planet that it had been studying for 13 years, after a seven-year voyage to Saturn,” Michael Watkins, the director of the Joint Propulsion Laboratory in Pasadena, said at a 6:30 a.m. news conference. “But continuing the legend of Cassini, it turned that event into an event of hope — not an end, but really a beginning.”
Watkins said that “the discoveries that Cassini has made over the past 13 years in orbit have rewritten the textbooks of Saturn, have discovered worlds that could be habitable, and have guaranteed that we will return to that ringed world.”
The spacecraft, whose mission was managed by JPL for NASA, was launched in 1997 and reached the ringed planet in 2004. The project was a collaboration between NASA, the European Space Agency and the Italian Space Agency, with teams from 17 countries comprising the joint team responsible for designing, building, and flying Cassini and collecting data from it. The craft has been in the “Grand Finale” of its scientific mission since April, when it shifted its orbit closer to the planet.
In mid-August, Cassini began a series of 22 passes through Saturn’s upper atmosphere. The close flybys allowed Cassini to take high-resolution images and collect data on Saturn’s auroras, temperature and vortexes at the planet’s poles.
On Monday, Cassini moved closer to its demise by zipping past Saturn’s moon Titan, a pass that shifted the spacecraft’s trajectory and sent it on a path into Saturn’s atmosphere.
NASA and JPL officials called the close encounter with Titan — at an altitude of 73,974 miles above the moon’s surface — a “goodbye kiss.”
Since that flyby, Cassini has been hurtling toward Saturn, taking its final photos and gathering its final data. The craft will continue its scientific mission to the very end, with eight of its scientific instruments operating and transmitting data for as long as they are able.
Cassini had been expected to begin its “final plunge” at 12:15 a.m., with JPL receiving data and confirmation of the maneuver about 90 minutes later.
The ship entered Saturn’s atmosphere at around 1,190 miles above the planet’s cloud tops, its thrusters firing first at 10 percent of capacity and then at 100 percent in hopes of keeping the ship’s transmitter pointed toward Earth. Again, it took about 90 minutes for Cassini’s signal to reach Earth.
At 3:32 a.m., the thrusters were no longer able to keep the ship stable as Cassini plunged into the planet’s atmosphere at a speed of about 70,000 mph, breaking apart like a meteor.
Its signal, however, continued to travel for about 90 minutes. The final evidence of Cassini’s existence arrived on Earth, as expected, at 4:55 a.m. California time, followed by words of congratulations from the project manager and a round of hugs and applauses. JPL officials said the end was bittersweet, “but mostly sweet,” one said.
“The spacecraft’s final signal will be like an echo,” Earl Maize, Cassini project manager at JPL, said hours before the last transmission was received. “It will radiate across the solar system for nearly an hour and a half after Cassini itself has gone. Even though we’ll know that, at Saturn, Cassini has already met its fate, its mission isn’t truly over for us on Earth as long as we’re still receiving its signal.”
Cassini’s final data was received on Earth at NASA’s Deep Space Network complex in Canberra, Australia.
Mission managers have hailed major achievements in the understanding of Saturn’s composition and the environment of its moons.
Cassini discovered icy jets that shoot from the moon Enceladus, allowing the collection of samples from an underground ocean that shows signs of hydrothermic activity. The ship also found evidence of liquid ethane and methane in Titan’s hydrocarbon lakes and seas, while also analyzing chemicals that form in the moon’s atmosphere and rain down on Titan. The ship also tracked a massive storm that circled Saturn for almost a year.
The mission’s end has been carefully planned to preserve Saturn and its moons,.
“The end of Cassini’s mission will be a poignant moment, but a fitting and very necessary completion of an astonishing journey,” Maize said. “The Grand Finale represents the culmination of a seven-year plan to use the spacecraft’s remaining resources in the most scientifically productive way possible.
By safely disposing of the spacecraft in Saturn’s atmosphere, we avoid any possibility Cassini could impact one of Saturn’s moons somewhere down the road, keeping them pristine for future exploration,” he said.
—City News Service