Titan, Saturn’s moon, boasts both freshwater rivers and saltwater oceans

The most detailed look yet at Saturn’s moon Titan’s strange lakes has revealed a diverse marine landscape similar to Earth’s, with a mix of freshwater rivers and saltwater oceans.

Unlike Earth’s watery oceans, Titan’s lakes are composed of methane and ethane, which are liquid at the planet’s average surface temperature, about −179 °C (−290 °F).

Radar measurements from NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, suggested differences in the lakes’ properties, including their composition and surface waves, but the signals didn’t contain enough information to distinguish between them.

now, Valerio Poggiali Poggiali and his colleagues at Cornell University in New York used a different radar technique to map the composition and surface of Titan’s oceans, revealing that the amount of ethane increases as you move south across the planet from the north pole. “The further north you go, the cleaner and purer the oceans become. They’re dominated by methane,” Poggiali says.

Previous radar measurements were made using signals sent and received at the same location on the Cassini spacecraft, which meant the reflected radio waves were polarized in one direction, or twisted.

The new study analyzed signals from Cassini’s radar that were reflected off the lake’s surface and picked up by NASA’s Deep Space Network, a radio antenna on Earth. The shallow angle of the reflected signal meant it contained two different polarized waves, giving Poggiali and his colleagues more information about the lake’s properties.

They found that many of the rivers and estuaries that feed the lake have rough surfaces caused by wind-driven waves, which could be a sign of active tides and currents feeding into the lake, Poggiali said. “Surface activity is very important if we want to plan future missions like a Titan submarine, but also to better understand Titan’s environment in terms of wind and atmospheric properties.”

Poggiali and his colleagues also found that the methane content was higher before the river flowed into the lake, which could help trace the methane and ethane cycle on Titan, Poggiali says. Ingo Muller-Wodarg “On Earth, when rivers flow into large, salty oceans, we find that the water becomes less saline near where the river flows in,” say researchers from Imperial College London. “Something similar is happening here, but it’s not the salinity that’s the problem, it’s the relative proportions of methane and ethane.”