A paper written by a University of Hawai'i researcher that describes the first storm observed in the tropical latitudes of Saturn's moon Titan will be published today in the journal Nature.

The paper's lead author, Dr. Emily Schaller, wrote it while working as a Hubble Fellow at the University of Hawai'i-Manoa's Institute for Astronomy.

The paper says that rain from large clouds such as those observed on Titan is actually liquid methane and may be responsible for forming the channels and other features near the equator observed by the Huygens probe in 2005.

The huge storm — observed with the NASA Infrared Telescope Facility and the Gemini North telescope on Mauna Kea — covered almost 1.2 million square miles, an area about the size of India.

While the diameter of Earth is 7,926 miles, Titan's is 3,193 miles, just slightly larger than Mercury, the smallest planet in our solar system.

Titan is the only moon in the solar system with a thick atmosphere, and like Earth, it has a weather cycle, including clouds and rain. However, on Titan, the substance that forms clouds and rains down on the surface is not water but methane. It is so cold on Titan (288 degrees below zero) that methane is a liquid, and there are "boulders" made of frozen water rather than rock.

Clouds on Titan are generally much smaller and occur much more infrequently than on Earth, which led scientists to wonder how the rivers and channels seen by the Cassini spacecraft and the Huygens probe were formed.

"After three years of observing Titan and finding little to no cloud activity, Titan suddenly put on quite a show," Schaller said.

Unlike the large channels on Mars, which were probably carved millions or billions of years ago by liquid water, Titan's carved surface features, like those on Earth, are still being formed today.

The other authors of the paper, "Storms in the tropics of Titan," are H.G. Roe of the Lowell Observatory and T. Schneider and M.E. Brown of the California Institute of Technology.