Dimming Hopes for Life on Titan, Saturn’s Largest Moon
For a considerable period, the prospect of life on Titan, Saturn’s largest moon, sparked considerable intrigue among scientists internationally. However, this optimism has recently been undermined by a new study, indicating that Titan’s subsurface ocean could, unfortunately, be inhospitable.
Implications of the Findings
These recent findings carry significant implications. The likelihood of discovering life on the four gas giants – Jupiter, Saturn, Uranus, and Neptune – has ostensibly diminished. “Unfortunately, this means we have to curb our expectations concerning the search for extraterrestrial life within our solar system,” remarks Professor Catherine Neish of the Western University in Canada. “Science has always been tremendously enthusiastic about discovering life in the icy worlds at the edge of our solar system. However, these findings show that this is less likely than we originally projected.”
Comet Impacts
The gas giants’ moons, replete with vast underground oceans brimming with liquid water, seemed to present the most suitable conditions for life. Titan, the second largest moon in our solar system, is believed to shelter an ocean beneath its icy crust that is twelve times the size of Earth’s oceans. “Life, as we know it on Earth requires water, hence planets and moons rich in water are particularly intriguing when searching for extraterrestrial life,” explains Neish.
To decipher whether life could indeed originate from this giant water body, Neish, along with her colleagues, attempted to calculate just how many organic molecules could potentially seep from Titan’s crust into the deep-sea bed. They used data derived from the impact of comets which led to surface melting, thus creating lakes of liquid water that mixed with organic matter. This blend, being denser than the icy crust of the planet, theoretically has the potential to sink through the ice into the ocean.
An Elephant Per Year
Subsequently, the researchers evaluated how many comets of different sizes struck Titan each year to predict how much water would seep through the terrain into the ocean. Unfortunately, the figures were less than promising – the rates of seepage amount to a maximum of 7500 kilograms of glycine per year, the simplest proteinogenic amino acid. This is roughly equivalent to the weight of a male elephant.
“An elephant per year of glycine in an ocean with twelve times the volume of Earth’s oceans is insufficient for life,” states Neish. “People in the past presumed that water equates to life, but overlooked the fact that life also demands other elements, like carbon.”
Best Contender
Other icy worlds, such as Jupiter’s moons Europa and Ganymede, essentially lack carbon on their surfaces. Thus, Titan was primarily considered the most viable contender for life within our solar system. If life cannot be sustained there, it’s highly unlikely it can exist anywhere else. “This study highlights how difficult it is to transport carbon from Titan’s crust to the subterranean ocean. Essentially, it’s quite challenging to access both water and carbon – indispensable elements for life – at the same location,” clarifies Neish.
The Dragonfly Mission
Although these conclusions may be somewhat disappointing, there is still plenty of work for NASA’s Dragonfly mission. Scheduled for launch to Titan in 2028, the Dragonfly’s primary purpose was to search for life. “It’s virtually impossible to decipher Titan’s surface composition with a telescope. We have to land there and gather samples,” asserts Neish, who contributes to the drone project.
So far, only once has there been a landing on Titan, and that was back in 2005; it remains the furthest landing point ever achieved by a spacecraft.
“Even if Titan’s subterranean ocean proves to be lifeless, we could still glean a lot of insights about the prebiotic composition of Titan, and Earth, by studying the reactions on Titan’s surface. We’re still quite keen to ascertain if any intriguing reactions occur, particularly where organic molecules mix with liquid water,” explains the scientist.
Still Much to Discover
When Neish initiated her latest study, she was concerned it might negatively affect the Dragonfly mission; instead, it precipitated even more queries. “If all the water had sunk through the ice crust, we wouldn’t be able to gather samples of water that had mixed with organic material on the surface. Now, the Dragonfly can focus on finding the products of these prebiotic reactions, thus teaching us something about how life might arise on different planets,” Neish elaborates.
“The outcomes of this study were even more dismal about the habitability of Titan’s ocean than I anticipated, but it also means there are even more exciting prebiotic areas near Titan’s surface from which we could retrieve samples using the Dragonfly’s instruments,” she concludes.
