After 13 years of orbiting Saturn and its moons, NASA’s bus-size Cassini probe is now a puff of radioactive vapor in the planet’s swirling clouds.
Space agency leaders knew this day would come since 2010, when they decided to empty Cassini’s tanks to continue exploring Saturn as long as possible.
Without a means of controlling the probe, they reasoned, Cassini had to be destroyed. This would prevent it crashing into Saturn’s icy moons Enceladus and Titan – which hide vast, salty, global oceans that may be habitable to alien life – since Cassini left Earth contaminated with small amounts of bacteria.
To honor the more than 453,000 photos Cassini took of Saturn, its rings, moons, and other objects, several NASA divisions worked together to select its 100 greatest visuals. Those have been turned into a 110-page ebook, titled “The Saturn System Through the Eyes of Cassini“, which is free to download for iBooks, Kindles, and other ebook readers (and just as a PDF).
“While these images represent the tip of the iceberg – each telling a story about Saturn and its mysterious moons – our hope is that the mission will inspire future artists and explorers,” NASA wrote in a press release. “The sheer beauty of these images is surpassed only by the science and discoveries they represent.”
Jim Green, NASA’s head of planetary science, wrote the forward to the collection of pictures.
“This book is the first chapter of what I predict will be the greatest story ever told: how humans reached for the stars and discovered life beyond Earth,” Green said.
Here’s a small collection of the best images and what they reveal.
The book includes beautiful views of Saturn. This image shows the planet’s north pole and the hexagonal blue-yellow storm there, which is big enough to fit several Earths inside.
Cassini snapped this photo of Saturn while passing through the planet’s shadow.
Saturn appears to float. In fact, the planet is so gaseous it’d float on water (if there was an ocean big enough).
Near-infrared photos revealed Saturn in a whole different light. (This image is colorized to highlight different wavelengths.)
The star of the Cassini mission was Enceladus: a small, ice-encrusted moon that hides an ocean.
Cassini even flew through jets of Enceladus’ ocean that shoot out of the moon’s south pole. The probe “tasted” the spray and revealed that the ocean was warm and possibly habitable to alien microbes.
Titan, Saturn’s largest moon (left), is the size of planet Mercury. Cassini used Titan’s gravity to change its orbit.
The probe’s views of Titan in front of Saturn were striking.
This shot shows Saturn’s second-largest moon, Rhea, eclipsing Titan.
Titan’s atmosphere twice as thick as Earth’s. The moon has clouds, weather, and even liquid lakes. Cassini caught this glint of sunlight reflecting off of Titan’s largest lake in 2009.
Near-infrared photos cut through Titan’s clouds and haze to reveal its complex surface.
In 2004, Cassini dropped off Huygens — a European-built lander — on Titan, leading to the first alien-moon landing in human history.
Ligeia Mare is Titan’s largest lake. It’s full of hydrocarbons like ethane and methane.
Cassini inventoried Saturn’s other weird moons, too, including Iapetus…
…And pockmarked Hyperion.
Dione, a small icy moon, is dominated by Saturn and its ring shadows.
Cassini also caught views of Saturn’s rings, which are now thought to be millions of years old.
The planet’s inner C-ring is almost translucent in this photo, showing the blue-hazed limb of Saturn’s atmosphere behind it.
Just like ice in Earth’s atmosphere, Saturn’s rings can produce rainbow-hued halos.
This weird view shows how Saturn’s outer atmosphere distorts light reflecting of rings behind it.
Though gossamer-thin, Saturn’s rings do have shapes. These roughly mile-high peaks cast shadows on nearby ring material.
The gravity of Prometheus — a small, potato-shaped moon lurking in Saturn’s F-ring — was found to create “streamers” in ring material.
This grainy image reveals a deep mystery of Saturn: “propeller objects” (the white streaks) that fail to carve out their own lanes in the rings.