Back when deciding to destroy Galileo, “it wasn’t easy to come to consensus,” says Torrence Johnson, the Galileo project scientist and a Cassini science-team member. “You had the analysis from the orbits, what the probabilities were, and what the scientific benefits of the things were. We thought, well, let’s just go out in a blaze of glory.” Throwing a billion-dollar science instrument into a giant ball of gaseous planet could allow them to do a close flyby by of Jupiter’s moon Io or get data from deep in the Jupiter magnetosphere.
Destruction of this kind is likely to be used again for the Juno mission currently orbiting Jupiter. “All of these missions are connected, and they build on each other,” says Jonathan Lunine, a Cassini science team member and now a co-investigator on the Juno mission.
Still, it’s extremely difficult for the team to let go of the spacecraft. Some members refer to the probes as their children. Many spend upward of 30 years on one mission. “It’s like in the death of a loved one—you look back and you think about all the good memories, the times you’ve shared together, went on vacation together, grandchildren,” says Spilker. “I think of it more like planning perhaps a wake.”
When it was time for Galileo’s end, the mission’s team issued a timeline of commands, the way they will do for Cassini and Juno. At 9:25 a.m., “the intensity of radiation interference [reached] a point where even a bright star like Vega can no longer reliably be seen by the attitude-control star scanner. The software [was] told to expect to see no more stars.” Three hours later, Galileo disappeared over the horizon of Jupiter. At 12:49 p.m., the signal was lost.
Cassini’s death will not pass without a vigil-like ritual. On September 15, thousands will gather at JPL and wait until the early morning hours for Cassini’s final orbit to begin. They’ll share stories of a lifetime of work, as that effort culminates in fireworks 800 million miles away.
Mission control will watch over the downlink for the last bits of Cassini’s data. It’s not known exactly how long it will take for Cassini to perish once its metal begins to melt in the clouds of Saturn, but it will be quick. In these final moments, like a dying person whispering their last words into the ears of loved ones, Cassini will pour out information as it dutifully descends lower and lower into Saturn.
When humans die, they release a final breath. The ancient Egyptians called this last exhale a “wind” that arrives to carry away a person’s soul to the afterlife. For Cassini, the impact from falling backward through the hydrogen-thick atmosphere will tear away its parts—first the large sections, then the instruments, until the antenna pointing toward Earth sends back one final beep. This message will breeze past Jupiter and Mars, through the solar plasma pushing toward deep space, and finally run into Earth, where it will be collected in the antennas of the Deep Space Network.
Cassini’s team will be there to feel the wind that’s traveled from the depths of the solar system. The probe’s final whispers will be sought-after science, whatever is discovered in those last moments. Then just like that, the grasp we’ve had on Cassini for 13 years will end. There will be no more commands to send, nothing else to say. The only thing to do will be to listen and to say goodbye.