The way star systems form – how they come to be, their behavior, their physics – is of great interest to astronomers, because they point directly to our genesis. How we came to be.
Our solar system – the Sun in the center, eight planets in pursuit, untold wonders far and wide – may be just one of hundreds of billions of comparable systems in the Milky Way. From all that we have seen, it is apparent that the laws of physics, beautiful and immutable, are the same no matter which direction we probe. Or what star we focus on.
What if we had a microcosm of our solar system that was so close we could send advanced spacecraft there, and land our cutting-edge probes there?
The problem is, all those countless other systems are so far away, they are tiny specks even in our largest telescopes. But what if we had a microcosm of our solar system that was so close we could send advanced spacecraft there, and land our cutting-edge probes there? If we had that, we could almost drop ourselves into a time machine and discover our cosmic origins.
Saturn is home to some of the most fascinating realms in our solar system. Our very best images (and scientific knowledge) of the planet come from the robotic explorer, Cassini. The Cassini spacecraft orbited Saturn for 13 years. Pixel by pixel, it collected data to beam back across the vast expanse towards Earth. There, the data form a massive catalog of nearly half a million images. These are stunning to look at, but they have also sparked new ideas about Saturn, about our own future ... and our past.
The Cassini mission to Saturn changed the course of planetary exploration forever. By recognizing that Saturn and its moons are analogues for the Sun and its planets, Cassini prompted scientists to rethink their understanding of the solar system as a whole. In this way, Cassini's discoveries opened up new avenues of research that could ultimately change the course of human history.
The Cassini mission allowed us to go back in time to see conditions similar to those in our nascent solar system 4.5 billion years ago.
Cassini discovered that Saturn’s rings are made almost entirely of water ice. And they are old, billions of years old. This disk of ice resembles one that surrounded the ancient Sun. Like Saturn’s rings, the Sun’s protoplanetary disk was a product of angular momentum and gravity. The Sun’s disk eventually coalesced into the planets, asteroids, comets and moons. Saturn’s disk is still here for us to examine. Like a portal through time, we can study the rings to gather clues about how planets form.
A staggering achievement of human and technical complexity
The Cassini mission allowed us to go back in time to see conditions similar to those in our nascent solar system 4.5 billion years ago. And while its pictures of the rings are fascinating and illuminating to say the least, they are a sideshow compared to the images taken of Saturn's moons. In some of them, we may be looking at the environs of actual life.
Until Cassini arrived, the moon Enceladus was just another frozen iceball, languishing in the blistering cold. Cassini detected an area of heat near the moon’s south pole. Curious, the spacecraft swooped in for a closer look and noticed plumes spraying up from strange slashes in the surface. The spray is water but also holds complex molecules sometimes associated with life. Careful measurements of the moon’s orbit confirmed a wobble caused by a sloshing layer of liquid below the icy shell.
Enceladus, once presumed to be a cold and dead world, is now one of the most likely spots for extraterrestrial life, perhaps like the kind that live in deep-sea hydrothermal vents on Earth.
Cassini revealed truths about our ancient selves by exposing details in the processes that formed our modern solar system, including our planet, and possibly even us.
Another moon is even more mysterious. Who would have expected to find the most Earth-like world we have yet found … in orbit around Saturn! Titan, Saturn’s largest moon, is bigger than Mercury and clings onto a thick, cloudy atmosphere.
When Cassini’s infrared instruments stripped away Titan’s thick blanket of clouds, it revealed an intriguing network of seas and lakes. These surface lakes are not made of water. They are liquid methane and ethane. But underneath, Cassini’s instruments detected another liquid ocean, made clear as Titan is squeezed and stretched in the intense Saturnian tides.
Could a different sort of life exist there right now? If we don’t look, we'll never know. One option is to send a submarine to Titan. Drift in the seas, beam back pictures of whatever aquatic wonders may exist. Another is to send a drone. Soar all across the moon, scan for potential habitability. The thick atmosphere and low surface wind speeds on Titan would permit the efficient flight of such a craft.
Science fiction or science fact?
It’s not fiction. NASA’s new Dragonfly mission to Titan, launching in 2026, will send an octocopter lander (a Mars rover-size, drone-like vehicle) that will be able to make multiple flights around the moon. It will explore and sample various locations on Titan, tens to hundreds of miles apart, in order to characterize the habitability of the moon’s environment, and even search for chemical hints of water-based or hydrocarbon-based life.
But for now, we still have mountains of data that Cassini brought us. This spacecraft carried humanity’s ambitions, hopes and curiosity and, incredibly, Cassini’s own discoveries were the cause of its demise. To avoid damage to any potential life at Saturn, Cassini was sacrificed. It nudged itself into an orbit that dipped into Saturn’s atmosphere, gradually slowing due to friction. The spacecraft eventually plunged into the planet, dutifully measuring, observing and transmitting right up until the end.
The spacecraft's legacy is one of engineering, ingenuity and most of all, discovery. Cassini has given us a tantalizing glimpse of the future. But, like a time traveler, Cassini revealed truths about our ancient selves by exposing details in the processes that formed our modern solar system, including our planet, and possibly even us.