Saturn, too, has polar aspirations. Like Jupiter, its atmosphere is hydrogen-rich with ammonia-ice clouds. In 2012, the Cassini spacecraft produced vivid photographs of a remarkable hexagonal jet stream — first detected in the 1980s by the Voyager probes — shooting point to point around the planet’s north pole.
That was seven years after it produced equally remarkable imagery of Saturn’s largest moon, Titan, which is far more interesting to astrobiologists. Nitrogen-rich with a dollop of methane and ethane, Titan is the only moon in the solar system with clouds and a dense atmosphere — four times heavier than our own. It is also the only world besides Earth that features liquid on the surface despite temps hovering near –300 F (–184 C).
Cassini also detected a subterranean saltwater ocean, lakes and seas of liquid methane near the poles, and vast stretches of arid dunes ringing the equator. And when Cassini launched the Huygens probe to Titan’s surface in 2005, photos revealed a fantastical landscape of misty haze, river channels, and dunes.
With an axial tilt of 27 degrees, Titan has seven-and-a-half-year seasons and methane rainstorms that are thought to flood polar rivers in summer. NASA’s eight-rotor Dragonfly helicopter will land at Titan’s equator in 2034 in search of life. The dense atmosphere (as compared to the ultra-thin air NASA’s Ingenuity helicopter deals with on Mars), should enable it to fly northward in a series of hops covering over 100 miles (160 km). Based on seasonal observations from Cassini, NASA forecasters predict calm weather.
“We think of Titan as a real-life laboratory where we can see similar chemistry to that of ancient Earth when life was taking hold here,” says astrobiologist Melissa Trainer, Dragonfly’s deputy principal investigator.