Titan, Saturn’s largest moon, is the only object in the Solar system other than Earth with liquids on its surface. Discovered through telescopic observations by Christiaan Huygens in 1655, Titan has rivers, lakes, and seas of methane and ethane liquids, which follow an evaporation and precipitation cycle similar to the water cycle on Earth.
How often does it rain on Titan? Clouds are known to exist in Titan’s lower atmosphere. However, rainfall is challenging to observe from a large distance. Theoretical modeling suggests rainfall that evaporates before reaching the ground. There is also indirect evidence for rain based on the observed surface darkening after the passage of a large storm front, followed by a lightening of the surface several weeks later.
Are there fish swimming in Titan’s rivers and seas? If they exist and I had the opportunity to catch some, I would have avoided the temptation to eat them because of related health risks from methane and ethane, both flammable gases. However, the mere existence of fish or any other living organism on Titan, would constitute life-as-we-do-not-know-it based on chemistry in liquids other than water.
Finding life on Titan would have major implications not only for the prevalence of life in the present-day Universe but also in the early Universe. The surface temperature of Titan is 94 degrees Kelvin, about a third of room temperature on Earth relative to absolute zero. This happened to be the temperature of the cosmic microwave background about a hundred million after the Big Bang when the first generation of stars formed.
An object like Titan forming out of matter enriched by heavy elements from the first supernovae, would have acquired this surface temperature irrespective of its distance from a star. As I wrote in a recent paper, the bath of cosmic radiation would have kept the Titan-like object warm for tens of millions of years, sufficiently long for primitive forms of life to possibly emerge on it when the Universe was just a percent of its current age.
NASA’s mission Dragonfly is planned for launch in July 2028 , with arrival to Titan in 2034. It will carry a robotic rotorcraft that will fly in Titan’s atmosphere with the goal of studying prebiotic chemistry. This quadcopter drone lander will possess a mass of about 450 kilograms, packaged inside a heat shield 3.7 meters in diameter. It will collect regolith samples on multiple locations by vertically taking off and landing. The craft can fly at a speed of about 10 meters per second, and reach altitudes of about 4 kilometers.
Dragonfly will carry meteorological sensors to measure atmospheric temperature, pressure, humidity, and wind speed, a seismometer to detect potential “Titan-quakes,” and a collection of cameras that will image each landing site, take microscopic images at the millimeter scale of grains of sand, and capture aerial photos as the rotorcraft flies between locations.
Titan’s atmospheric pressure is 1.5 larger than Earth’s and its surface gravity is 14% of Earth’s. As a result, the required flight power per payload mass is about 40 times lower than needed for flights around Earth.
About 17% of Titan’s surface is covered by dune fields, mostly at latitudes between plus or minus 30 degrees. Dragonflywill provide important information about the dune properties but only over a small region of Titan’s surface. It will not deliver a high-quality global map of Titan.
The detailed compositions of Titan’s lakes and seas are important for studying the prospects for it to host life, since prebiotically relevant organic structures can form in these liquid reservoirs and also condense from the atmosphere. If Dragonfly detects exposed water ices on Titan’s surface, that finding could be indicative of recent endogenic or exogenic activity, since much of the surface might be covered by organics that accumulate from Titan’s atmosphere.
I realize that my wish to go fishing on Titan may not be granted in the short time that I have left to live. But I am content with relying on Dragonfly to provide me some clues on what forms of life may exist within Titan’s lakes, rivers and seas.
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s – Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011-2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.