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 to 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…