For the first time, astronomers at California Institute of Technology (Caltech) spotted fog on the surface of Titan.

Titan is is the largest moon of Saturn and described as a planet-like moon. Titan has a diameter roughly 50% larger than Earth’s moon and is 80% more massive. It is the second-largest moon in the Solar System.

Astronomer Mike Brown, said that Titan probably the only place in our entire solar system to have liquid (largely, liquid methane and ethane) sitting on its surface.

He and colleges were excited about the new discovery and they presented their work Today at the American Geophysical Union’s 2009 Fall Meeting in San Francisco.

“Fog—or clouds, or dew, or condensation in general—can form whenever air reaches about 100 percent humidity,” Brown says. “There are two ways to get there. The first is obvious: add water (on Earth) or methane (on Titan) to the surrounding air. The second is much more common: make the air colder so it can hold less water (or liquid methane), and all of that excess needs to condense.”

In 2008, Cassini confirmed liquid methane lakes in Titan’s southern hemisphere using infrared data. But it took until now to analyze the data and connect the pieces together.