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MIT Technology Review

Fog Discovered at Titan’s South Pole

The discovery is the first direct evidence of an Earth-like hydrological cycle.

We’ve suspected for many years that something remarkable is going on on Titan, and yet the evidence to nail this conjecture has been strangely difficult to find.

The idea in question is whether Titan’s atmosphere actively shapes its surface, as occurs on Earth. There’s no shortage of evidence that hints at a complex, vibrant climate with rains that have carved streams and rivers into the surface of Saturn’s largest moon, creating lakes and shorelines in the process.

But all this could be misleading, say Mike Brown at Caltech and a few pals. They put it like this:

“It is possible that the identified lake features could be filled with ethane, an involatile, long-term residue of atmospheric photolysis; the apparent stream and channel features could be ancient from a previous climate; and the tropospheric methane clouds, while frequent, could cause no rain to reach the surface.”

The drizzle that astronomers have seen appears at such a high altitude that it probably evaporates before it hits the ground.

In this context, the importance of the discovery of fog at Titan’s south pole cannot be underestimated (coming courtesy of images from the Cassini spacecraft).

On Earth, fog can form in a number of ways, but most of these mechanisms cannot work on Titan. “Fog on Titan can only be caused by evaporation of liquid methane,” the team says. “The detection of fog provides the first direct link between surface and atmospheric methane.”

And that’s important why? First, because it’s evidence of a hydrological cycle in which an evaporating liquid on the surface enters the atmosphere. And second, because it finally confirms Titan as an active meteorological body in its own right.

Ref: Discovery of Fog at the South Pole of Titan