Cassini observed Titan for half a Saturnian year, from northern winter to northern summer; now that the Cassini mission has ended, ALMA will be able to observe how the atmosphere changes over the remainder of Saturn and Titan’s year – and how the abundance of organic molecules changes with it. For example, analysis of Cassini data by the NAI team has found seasonal variations in the C3Hx hydrocarbons such as propane and propyne in Titan’s stratosphere.

The remaining investigations as part of Objective 1 involve understanding how molecules are transported across the surface after they have precipitated out of the atmosphere, which is a task being led by Alex Hayes’ group at Cornell University. The next step is to understand how the organics are modified at the surface, and then how they are moved from the surface to the ocean.

This latter query has yielded a surprising possibility. One of the main results from the project so far is a paper by Kelly Miller, Hunter Waite and NAI team-member Christopher Glein of the Southwest Research Institute in Texas, which proposes that Titan’s nitrogen atmosphere originates from organic molecules that were trapped inside Titan when the moon formed, and the subsequent heating of these gases released nitrogen that seeped up to the surface. For the purpose of the NAI project, it suggests that there are already organics inside Titan that could enter into the ocean from below, so even if organics cannot reach the ocean from the surface, the ocean could still contain life’s building blocks.

“These organics may actually be able to percolate up through cryovolcanism,” says Lopes, creating a possible origin too for some of the organics on Titan’s surface.

Objective 2: Habitability

If pathways exist for organics to pass through the ice shell from the surface to the ocean below, then the next step is to figure out whether the ocean, or anywhere in the ice on the journey to the ocean, is potentially habitable. This is where the biologists on the team, studying high-pressure, cold-tolerant organisms, come into play.

Before that can be done, more needs to be known about the ocean. Although Cassini confirmed that the ocean exists via gravity measurements, “What we don’t know is the exact composition of the ocean, its density, its thermal profile, the overall structure of the icy crust on top of it,” says Malaska.

To better understand the ocean and its potentially habitability, researchers on the team start off with several possible compositions that could reasonably be expected to exist, and work backwards, developing theoretical models.

Although it may be impossible to ever directly explore the deep subsurface or ocean of Titan, the NAI team intend to use both theoretical modeling and laboratory experiments to simulate the possible conditions, to better understand the interface between the ice shell and the ocean, and the ocean with the rocky core, and the flow of oxidants and reductants at these interfaces that could support microbes.