In August 2009, NASA’s Cassini spacecraft became the first robotic emissary from Earth to witness an equinox at Saturn, when the sun was shining directly on the giant planet’s equator.
Saturn has been our companion since the dawn of humankind, wandering across the heavens as one of the brightest dots of light visible to the naked eye. Ancient cultures as far back as Babylon tracked its movements; many people thought the creamy-colored star represented a divine presence.
Now, a spacecraft that turned this dot of light into a cosmic wonderland is about to make the ultimate sacrifice for science and hurl itself into Saturn’s atmosphere, plunging deep inside the gas giant until gravity and friction rip it apart.
NASA’s Cassini spacecraft built upon the work of the Voyager mission, twin probes that sailed past Saturn in the 1980s. The Voyagers redrew our understanding of the planet’s stormy face and gathered the first tantalizing hints that some of its moons might be more active than expected. But the twins spent only a few weeks at Saturn and then parted ways, each heading farther into the solar system.
With its arrival in 2004, Cassini became the first spacecraft to actually orbit the ringed giant. For 13 years, has been circling Saturn in tangled loops, pirouetting past rings and moons to capture some of the most detailed views ever of these exotic objects.
The images and data sent back to Earth opened the celestial floodgates. Through Cassini’s eyes, we saw a menagerie of more than 60 moons—some small and pockmarked with craters, some large enough to hold oceans and dense atmospheres. We saw diminutive balls of ice sculpting Saturn’s rings and titanic storms raging across the planet. And Cassini gave us the first close look at Saturn’s atmosphere shifting with the seasons.
A few times, the probe even turned its eyes homeward and took snapshots of Earth, a pale blue dot drifting behind the veil of another world's rings.
In a few short days, Cassini will dive to its doom—but the mission leaves a rich legacy in the form of spectacular images and profound scientific insights. After all, the probe is being sent to its death so that we can protect two moons that Cassini tells us may be refuges for exotic forms of alien life.
Such mysteries are far too enticing to ignore. Perhaps someday, another robotic explorer will sail toward Saturn and turn up wonders we have yet to imagine.