When Cassini was launched in 1997, President Bill Clinton was being investigated for making fund-raising calls from the White House and the internet was in its infancy. Cassini, which arrived at Saturn in July 2004, has been a worthy successor to Voyager, no slouch in racking up some 4 billion space miles, circling Saturn and swinging on Titan’s gravity again and again to launch itself on a new course toward one or another strange moon.
Saturn’s little corner of the universe proved to be weirder and more diverse and promising than anyone could have predicted: the six-sided storm that hugs the planet’s North Pole; the mysterious plume-squirting moon Enceladus; and the bedazzling rings, spidery threads of ice, rock and dust — cosmic detritus shed over the ages by comets and meteorite collisions, woven by gravity into warps, braids, knots, walls, as iridescent and changeable as an oil slick.
To Cassini will go the credit for discovering what many astronomers think is the most likely place to find evidence of life beyond Earth. That would be Enceladus, which the spacecraft found is shooting plumes of salty water out of cracks in the ice that makes up its surface.
It turns out that Enceladus is mostly water — an “ocean world,” as NASA has now labeled many of the outer solar system moons. And an examination of the plumes recently detected the presence of hydrogen, suggesting there is hydrothermal activity, that is to say, energy and heat on the bottom of that ocean that could provide food for microbes.
Many scientists would now like to fly a probe equipped to detect microbes through a plume, to see if anything alive is taking a ride into space. It wouldn’t have to land and drill, as a similar effort on Europa, one of Jupiter’s moons, might require.
Others are not so sure. Mary Voytek, NASA’s director of astrobiology, recently threw cold water on the idea. Comparing that hydrogen gas with a stack of uneaten pizzas, she suggested there might be nothing on Enceladus to metabolize the energy.
Cassini also gets bragging rights for exploring Titan, perhaps the strangest moon in the solar system. When Voyager went by it in 1980, it was just a promising smoggy ball, the only moon in the solar system with an atmosphere even thicker than Earth’s. Cassini’s Huygens probe landed in a frozen world of methane dunes and river beds, among other forms of hydrocarbon slush. Its radar has detected oily lakes of methane and ethane that might be fizzing nitrogen bubbles like newly poured champagne.
What kind of chemistry might be slouching toward life on such a world? Along with an Enceladus probe, a boat to sail Titan’s methane seas has appeared on the wish lists of planetary scientists.
One reason scientists want to make sure Cassini is incinerated at the end of its journey is to ensure that any of its earthborn microbes do not contaminate the biotic or prebiotic worlds out there. Just in case.
With all this, it is fitting that Cassini’s end should come with a swan dive through those fabled rings.
For as long as humans have looked up with telescopes, the finest, most alluring thing they could see was the ringed planet. Galileo, the first one to see the rings, never knew what he was looking at. They have been a symbol of mystery ever since, of ineffable things just beyond our reach.
Now we have extended our reach.
Nothing Cassini has done or found so far has moved the markets back here on Earth. It moved only our souls, our minds and our imaginations. It made us freer and bigger by showing how little we know and how much more room there is to expand our thoughts and dreams. How little of nature’s repertoire we have even guessed at.
On July 19, 2013, we all smiled as Cassini took a long-range portrait of Earth. The Earth popped up again peeking through the rings like an eager child looking through the blinds on April 12. That’s us, a little blue dot below the ring plane. A little world of hustlers and dreamers.
An article on Saturday about the end of NASA’s Cassini mission misstated a date on which the spacecraft took a long-range portrait of Earth. It was July 19, 2013, not a month earlier.