Titan, the largest moon of Saturn, is often considered a potential candidate for hosting life. It is the only place in the solar system, besides Earth, where surface liquids are confirmed to exist, including rivers, lakes, and seas. However, a new study by NASA challenges this assumption and suggests that Titan’s ocean, and similar oceans inside other icy moons, may lack the organic chemistry necessary for life.
The problem of organics
The study, led by Catherine Neish of Western University in Ontario, Canada, and published in the journal Astrobiology, argues that for Titan’s ocean to be habitable, a large supply of organic molecules from the surface must be able to reach the ocean in order to facilitate prebiotic chemistry that can produce and feed life. The route for this organic material to reach the ocean is via comet impacts. Such impacts can melt surface ice, creating a pool of liquid water filled with organic molecules. Because liquid water is denser than ice, it sinks.
But, Neish’s modeling found that the rate of impacts is not high enough for sufficient organic material to reach Titan’s ocean. For example, Neish’s team estimates only about 7,500 kilograms (16,534 pounds) of the simplest amino acid, glycine, reaches Titan’s ocean every year. That’s equivalent to the mass of one male African elephant spread across an ocean with a dozen times the volume of Earth’s oceans.
“It’s like having a bathtub filled with water and then adding one drop of food coloring,” Neish said in a statement. “The concentration of organics in the ocean would be very low — too low to support life as we know it.”
Other sources of organics
The researchers also considered other sources of organics for Titan’s ocean, such as hydrothermal vents or serpentinization (a chemical reaction between water and rocks), but found them unlikely or insufficient as well. They concluded that Titan’s ocean is probably too cold and too isolated from the surface to sustain life.
Implications for other icy moons
The study has implications for other icy moons in the solar system that are thought to have subsurface oceans, such as Enceladus, Europa and Ganymede. These moons may also face similar challenges in delivering enough organics to their oceans.
“Titan is unique in having this very thick atmosphere full of organic molecules,” Neish said. “But even with that advantage, it still doesn’t seem like enough material gets down into the ocean. So for these other moons that have much thinner atmospheres or no atmospheres at all, it seems even less likely that their oceans would be habitable.”
Possibility of alternative life forms
The study does not rule out the possibility of life on Titan or other icy moons entirely, but it suggests that such life would have to be very different from Earth’s life and rely on other sources of energy and nutrients.
“Life finds a way,” Neish said. “Maybe there is some weird form of life that doesn’t need organics or maybe there is some other way to get organics into these oceans that we haven’t thought of yet.”
Recent Blog : Ancient Viruses Shaped Human Bodies: Study