With its wealth of hills, lakes and waterfalls, Ithaca certainly is “gorges.” But so is Saturn’s moon, Titan. In fact, Prof. Alexander Hayes, astronomy, and his team have discovered that Titan too features deep canyons. The resemblance is so striking that these Earth-like features can provide crucial information on the evolution of our own planet. The only difference though is that Titan’s canyons are filled with liquid methane.
Hayes traces the team’s success to NASA’s Cassini spacecraft, which has been orbiting Saturn and correspondingly, Titan, for 13 years.
“Even though people have been working on Cassini for twenty years or more, they still welcome early career scientists, be it graduate students or faculty, to come in and work on the mission with them,” Hayes said. “Because of that adaptability and willingness to bring in the next generation, we have come up with new ways to use Cassini’s instruments to make discoveries on Titan.”
One such method used Cassini’s radar for ranging, which works by sending out a pulse of energy and measuring the time it takes to come back, thus giving astronomers an estimate of how distant a surface is. Coincidently, the data recovered is very sensitive to the surface’s roughness.
“You have a very accurate measure of how smooth the surface is by seeing whether or not the radar reflects like a mirror or like a rough surface,” Hayes said. “So if you’re looking for waves, one way to do it is to shine the radar, look at the reflected light and see if the returned intensity suggests a surface that is perfectly smooth or one with waves on it.“
Hayes acknowledges the contribution of Valerio Poggiali, a visiting student from Sapienza University in Rome. By looking over Cassini optometry data for dry land, Poggiali observed mirror-like reflections from Titan’s channel beds and was thus, the first to directly observe that they contained liquid.
“Poggiali was able to say that these were not just channels, but liquid-filled canyons with a width equivalent to the Mississippi River,” Hayes said. “However, the Mississippi has a very gradual slope to it, while these channels [on Titan] are like the gorges of Ithaca that go straight down by 100 to 300 meters with slopes of 45 degrees or larger. What this means is that Titan’s river channels are much more vertically eroded than we thought.”
However, unanswered questions still remain, such as where all this eroded material goes.
“That’s the million dollar question,” Hayes said. “That’s the question we don’t have the answer to — where is all this material going? Not simply with the gorges, but also with the depressions that make up small lakes, since the latter appear to have no obvious outflow channels.”
However, Hayes believes that there are a number of theories astronomers could explore.
“Could it be that they form sediment plumes that uniformly fall on the seafloor so you don’t actually see concentrated deposits? Maybe. Another option is that the material dissolves in the liquid and the liquid flows somewhere else and there’s a subsurface storage of saturated liquid that has dissolved all the material of all these solid particles,” Hayes said. “I think this question requires a follow up mission – to actually get down there and measure the composition of the lakes and seas and makeup of Titan’s solid surface.”
picture courtesy of Prof. Alexander Hayes
LIquid methane fills canyons on Titan’s surface
Titan’s methane based hydrologic system seems similar to our own water cycle and determines how these canyons are filled. Thus, besides helping scientists build a comprehensive view of our solar system, Hayes believes that such similarities sufficiently justify its continual study.
“On Titan, we can study processes affecting its surface that are very similar to the ones that we have here on Earth. People say we want to study Venus because Venus is Earth’s greenhouse effect taken to extreme measures,” Hayes said. “You can say the same thing for Titan but instead of the greenhouse effect you would be talking about the hydrologic system. Titan is Earth’s hydrologic system taken to extreme measures. If you want to understand Earth’s hydrologic system and how our surface evolved, studying Titan will give you an example with very different conditions that you can use to test your models.”
But missions that allow us to do this could be in jeopardy. Due to budget cuts, many NASA missions in the pipeline are extremely targeted. Haye’s discoveries, on the other hand, were the result of a much more open-ended mission that gave astronomers the opportunity to explore Saturn without too many constraints.
Hayes refuses to give up and is working on future missions that may give a new generation of astronomers the opportunity to learn even more about this icy world.
“One concept I’m working on is an orbiter: to go to Titan, to get a complete view of the surface and understand things in much greater detail than Cassini was able to,” Hayes said. “The other mission is a lander that could land on the surface to do in-situ measurements and see what Titan’s surface is made of.