Saturn’s Moon, Titan: An Explorer’s Utopia

Alexander G. Hayes, Astronomy, refers to Titan as his first research love. “Where else can you say it’s raining right now, other than on Earth?” he says of Saturn’s largest moon. “It has strikingly similar processes acting on its surface, generating landforms including lakes, channels, and dunes—everything you have here, you have there. Titan’s methane-based hydrologic system works just like Earth’s water cycle, but does so in a completely alien environment.”

For those and other reasons, Titan is an “explorer’s utopia,” says Hayes. His focus is on analyzing and interpreting data captured by NASA’s Cassini-Huygens spacecraft, which has been orbiting Saturn and its moons since July 2004. Specifically, Hayes is interested in using data from the Cassini RADAR instrument to study interactions between Titan’s subsurface, surface, and atmosphere.

Hayes first began studying Titan as a graduate student at Caltech. Cassini RADAR team leader and Jet Propulsion Laboratory Director, Charles Elachi, visited the school and unrolled a 20-foot long print right outside of Hayes’ office. On it was a giant radar swath taken of the moon in July 2006. “I was hooked,” says Hayes.

Lakes, Dunes, Rain

Like Earth, Titan has lakes and seas. Only Titan’s lakes are made of methane and ethane, similar to liquid natural gas. Like Earth, Titan has dunes. Only the dunes are made of particles that are more like plastic than they are silicate sand. Like Earth, Titan has rain. Only the rain is made of methane and ethane, and it slowly falls from the sky in droplets much larger than we are used to here on Earth. Like Earth, Titan has rocks. Only the rocks are made of ice and organic solids.

“It’s taking the same physics, but applying it to extreme environments,” Hayes says. “It really tests our knowledge of how the processes that shape planetary surfaces work.” In many ways, Titan is a natural laboratory for studying the processes that shape all planetary surfaces, including Earth.

There’s still so much more to learn about Titan itself. Students and researchers in Hayes’ lab are working on a variety of projects to better understand the planet-like moon. They work on questions related to the depth and composition of Titan’s lakes, how the lakes interact with the moon’s atmosphere and solid surface through processes like evaporation and wind-waves, the composition and structure of Titan’s dunes, what the dune’s flow patterns tell us about the moon’s climate history, how wind patterns interact with Titan’s topography, and more.

Hayes’ lab has recently analyzed data that provide insight to the composition and depth of Titan’s lakes. In a surprising discovery, Cornell research associate Marco Mastrogiuseppe analyzed radar measurements that indicated the lakes are extremely transparent to microwave radation. The radar energy was able to see through more than 160 meters of Titan’s second largest sea, Ligeia Mare. In comparison, that same radar energy can see through only a millimeter of liquid water on Earth.

“This opened a whole new paradigm for us on how to study Titan,” Hayes says. “Just in the past year we’ve really turned everything we know about Titan’s lakes and seas on its head. The next several years of the Cassini mission are shaping up to be some of the most dramatic and exciting of the entire mission.”

Hayes says that he had never thought the lakes and seas were as transparent as the new radar measurements show. In cooperation with the Cassini RADAR Science Team, the researchers have redesigned spacecraft observations to take advantage of this discovery and are conducting further measurements of Titan's other seas. These measurements also provide insight into the composition of the liquid found on Titan, allowing the researchers to better understand how the lakes and seas interact with the moon’s atmosphere and subsurface.

In another recent observation, Hayes’ lab has seen the reappearance of a “magic island” in one of Titan’s seas. The island first appeared in July 2013, disappeared, and became visible again this past summer. The researchers are now trying to figure out what it is, and whether waves or floating debris on the seas might cause this transient “island” to reappear. When it was first spotted in 2013, Hayes, Professor Jonathan Lunine, and their student Jason Hofgartner hypothesized that it might be waves, rising bubbles, or floating solids.

The surface changes also reinforce predictions that Hayes and his colleague Ralph Lorenz at Johns Hopkins Applied Physics Lab made in 2012 and 2013. They predicted that Titan’s winds would freshen in the spring and summer and lead to wind-waves on the surface of the lakes and seas. Further measurements of surface activity were taken in January 2015 to see if these theories are accurate.

A Look at Saturn’s Ring

Since the Cassini spacecraft isn’t spending all of its time at Titan, neither is Hayes’ lab. One graduate student, Zhimeng Zhang, is studying Cassini RADAR measurements of Saturn’s rings. To better understand the origin of Saturn’s rings, Zhang is using microwave thermal emission measured both by Cassini and Very Large Array in New Mexico to look at the ratio of non-icy material to icy material. The rings are made up of greater than 90 percent icy water ice, and the amount of contaminant rock is indicative of both the ring’s age, origin, and the composition of the source material.

“Titan’s methane-based hydrologic system works just like Earth’s water cycle, but does so in a completely alien environment.”

In a recent measurement, the researchers saw that Saturn’s C ring, the ring closest to the planet, shows a hump of non-icy material near its center. The researchers interpret the data to suggest that an object affected the ring some 10 million years ago, and that the modern C ring is perhaps the youngest of Saturn’s rings. (A paper about the work is in progress.)

A Long-Term Interest

Hayes says that he knew he wanted to work as an astronomer since high school. He attended Cornell as an undergraduate with the specific intention of working with Steven Squyres, Astronomy. It worked out, and Hayes conducted undergraduate research with Squyres and Jim Bell, Astronomy, on the Mars Exploration Rover Program. On coming back to Cornell, Hayes says that “it was always the goal.” Today, he continues to collaborate with Squyres and other Cornell researchers on current Mars rover missions as well as helping to build and calibrate instrumentation for future missions, including the Mars 2020 rover and Europa Multiple Flyby Mission.

Still, Hayes says that his interest lies mainly in the outer solar system, and especially in Titan. “Mars is great, it’s fun, and the data is of such high quality that we can employ the same techniques as terrestrial geologists. As a result, missions are generally focusing on very targeted questions,” he says. “In the outer solar system, we don’t even know those questions. That idea of exploration, figuring it out for the first time, having big questions—that’s what really excites me.”