After 13 years of orbiting the Saturn system, and 4.9 billion miles logged, the Cassini mission has ended. The orbiter-turned-atmospheric probe is gone, vaporized on re-entry and now one with the planet.
At 4:55 a.m. (PDT), as predicted, the team received confirmation of the spacecraft’s demise when the radar graphs displayed loss of signal, signifying that the high-gain antenna could no longer remain steadily pointed toward Earth. The robotic explorer entered Saturn’s atmosphere at 9.4°N, 53°W.
The perfection of the probe was reiterated several times throughout the post-plunge briefing, as it was praised for having accomplished exactly what it set out to do. The probe was deemed successful to the very end.
“We believe we got every last second of data,” program manager Earl Maize said with confidence.
Maize talked about the legacy of the spacecraft, having laid the foundation, both with respect to science and engineering, for the next set of missions. A mission to Europa will utilize the engineering expertise and techniques as well as the sophisticated instruments developed for Cassini.
There will be much analysis to come of the final data sent to Earth. Eight of Cassini’s science instruments were active during atmospheric entry, collecting data on the Saturn’s gravity as well as its atmosphere’s hydrogen to helium ratio. Both parameters are key to studying the ringed planet’s internal structure.
Project scientist Linda Spilker explained that measurements such as the hydrogen to helium ratio require the physical presence of the spacecraft. “You can infer [the ratio], you can model it, but to be there and directly measure and sample, that was absolutely amazing,”
The spacecraft survived about 30 seconds longer than expected, said Cassini operations team manager Julie Webster (JPL). The team of scientists and engineers continues to work on assessing the data they collected during those final moments. “And I’m sure they’ll be very happy,” Spilker added gleefully, “that Julie was able to get the spacecraft to survive those extra seconds as we plunged on in.”
But future missions still have much to learn at Saturn. The potential for life in the global ocean of the tiny moon Enceladus, as well as the potential for astrobiology in the oceans of Titan intrigue scientists and excite the public. Spilker noted other unsolved mysteries, too, including the source of methane in Titan’s atmosphere and the power source for the hexagonal storm that rages at Saturn’s pole.
The last bits of visual data received were both heartfelt and compelling.
But it was the sequence of Enceladus setting behind Saturn, taken on September 13th two days before Cassini's farewell, that seemed as like a curtain falling at the end of the first act of an ongoing story.
Perhaps Earl Maize described the curtain call perfectly: “Cassini going out with an empty tank of gas at the very top of its game in a scientifically unexplored environment.”
Act two beckons.