NASA’s Cassini spacecraft melted into Saturn’s atmosphere today, ending the 20-year mission that sent back troves of data about Saturn, its many moons, and its glorious rings. Cassini project scientist Linda Spilker captured the mood by noting that if there was one thing she could say to the probe, it would be “Thanks for the ringside seat….We’ll be back.”

Cassini was launched in 1997. After a seven year journey, it finally reached Saturn in 2004 and has been orbiting the planet for the past 13 years. The statistics on how many bits of data and number of images it sent back to Earth is staggering. Scientists will continue to comb through it for years, probably decades, to come.

NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, CA designed, built and operated Cassini in partnership with the European Space Agency (ESA) and the Italian Space Agency (ASI). Cassini cost $3.67 billion including launch, of which $2.6 billion was paid by the United States and the rest by ESA and ASI. ESA built the Huygens probe that separated from Cassini and flew down through the haze that surrounds Saturn’s intriguing moon Titan, providing amazing images and data about the atmosphere and surface. (The mission is sometimes referred to as Cassini-Huygens rather than just Cassini.)

The years of development were not easy and costs grew. NASA had obtained permission from Congress to build Cassini and a sister spacecraft, the Comet Rendezvous Asteroid Flyby (CRAF), on the basis that money could be saved by building two spacecraft using the same design (Mariner Mark II). At the time, it was called the CRAF/Cassini program with a total program cost of $1.6 billion.

Congress was skeptical, however, and agreed only on the basis that if costs exceeded that $1.6 billion, one of the two would have to go. That is indeed what happened. CRAF was cancelled. Cassini was the survivor.

Members of the Cassini team, some of whom worked on the program for three decades, from design through the end of the mission today, expressed a range of emotions over the past three days of events at JPL heralding the end of the mission. At this morning’s press conference, project manager Earl Maize appeared a little teary when he said that Cassini had been a faithful companion all these years, but added this also is a time of “serenity” knowing that “we did what we needed to do.” Spacecraft Operations Manager Julie Webster said she thought she would be sad, but instead felt OK because the spacecraft had done everything that had been asked of it. Spilker said it was a time of “tears and applause,” but is optimistic that NASA will launch another probe to Saturn sometime soon.

NASA associate administrator for science Thomas Zurbuchen and planetary science division director Jim Green have been asked that question several times in recent days — when will the next Saturn probe be launched? Green points to NASA’s competitive New Frontiers program, which is currently evaluating proposals for the next in that series of missions that are cost-capped at $1 billion for development. The call for proposals included missions to study Saturn’s moon Enceladus, which is thought to have a liquid ocean under an icy crust (not unlike Jupiter’s moon Europa); to further study Saturn’s moon Titan, with its methane seas; and to send a probe down through Saturn’s atmosphere.

The date for when the choice will be made has not been announced. Other destinations for which proposals could be made were a comet surface sample return, a lunar South-pole Aitken Basin sample return, a Trojan tour and rendezvous, and a Venus In Situ Explorer. As always, there are many more places scientists want to explore than NASA’s budget can accommodate.

For now, getting new data about Saturn is done. Cassini’s last signals were received on Earth at 7:55 am Eastern Daylight Time as the spacecraft disintegrated in Saturn’s atmosphere. NASA deliberately destroyed it to ensure it did not accidentally impact — and thereby contaminate — Titan or Enceladus. If life is discovered on one of the moons, scientists want to make certain it is indigenous and not delivered from Earth.

Spilker said “Things will never quite be the same” for the Cassini team, but “we take comfort knowing that every time we look up at Saturn in the night sky, part of Cassini will be there, too.”