Carolyn Porco had an idea for a planetary selfie. Cassini would photograph Earth from nearly a billion miles away, our world a point of light beneath Saturn’s rings. She wanted everyone to know when the picture would be taken, so they could look up and wave.
I photographed Carolyn at Fort Funston in April 2021, with wind coming off the Pacific in great gusts. Birds soared above the cliffs, and the last daylight stretched golden across the water. We spoke about Carl Sagan and Pale Blue Dot, the Voyager image of Earth suspended in sunlight. I was interested in how a photograph could make an almost unimaginable distance feel personal. Carolyn had spent much of her career doing precisely that.
She led Cassini’s imaging team. Launched in 1997, the spacecraft reached Saturn in 2004 and spent thirteen years exploring its system. Its cameras recorded storms turning through the atmosphere and moons disturbing the rings. Shadows revealed structures that different lighting had concealed. With repeated observations, a distant planet became a place where scientists could follow events as they unfolded.
The images also allowed them to investigate what they could not see directly.
In 2005, Cassini revealed jets of water vapor and ice erupting near the south pole of Enceladus, a small, frozen moon. Later, Carolyn and her colleagues tracked surface features across years of photographs to measure a slight wobble in its rotation. The wobble was too large for the icy shell to be rigidly attached to the interior. A global ocean lay between them.
A world far from the Sun held liquid water beneath its surface. Better still, material from that hidden ocean was escaping into space, where spacecraft instruments could sample it. Enceladus became a compelling place to search for conditions that might support life. The discovery widened our sense of where a living world could exist.
Carolyn also wanted the images to reach people who would never study the measurements. Her idea became The Day the Earth Smiled, in July 2013. Cassini’s cameras gathered the images for a sweeping mosaic of Saturn and its rings, with Earth in the distance. People were invited to wave toward Saturn while their planet was being photographed. For a moment, anyone could participate in a mission exploring the outer solar system.
On the cliffs, we talked about Cassini’s end. In September 2017, the spacecraft was deliberately sent into Saturn’s atmosphere to prevent a future collision that could contaminate Enceladus or Titan. Carolyn described the loss as that of an old friend. A machine that had supplied years of discoveries would send nothing more.
The wind pulled at our jackets as the light faded. I kept thinking about her invitation to look up while Cassini looked back. Its cameras could never resolve a waving hand. Carolyn had still found a way to include us.
