An astrobiologist has discovered that Titan may not have enough amino acids to support life. A study conducted by Western astrobiologist Catherine Naish shows that the subsurface ocean of Titan, Saturn’s largest moon, is likely an uninhabitable environment; This means that any hope of finding life in the icy world is dead in the water.

This discovery means space scientists and astronauts are much less likely to find life in the outer solar system, which is home to four giant planets – Jupiter, Saturn, Uranus and Neptune.

“Unfortunately, we now need to be a little less optimistic about finding extraterrestrial life in our solar system,” said Naish, a professor of earth sciences. “The scientific community has been very excited by the discovery of life on icy worlds in the outer solar system, and this discovery suggests that this may be less likely than we previously thought.”

Impact on the search for extraterrestrial life

Detecting life in the outer Solar System is of significant interest to planetary scientists, astronomers, and government space agencies such as NASA, because many of the icy moons of giant planets are believed to have large subsurface liquid oceans. This. For example, Titan is believed to have an ocean beneath its icy surface whose volume is 12 times greater than the volume of Earth’s oceans.

“Life as we know it here on Earth requires water as a solvent, so water-rich planets and moons are interesting for the search for extraterrestrial life,” said Naish, a member of the Western Institute of Earth and Space Exploration.

In a study published in the journal AstrobiologyUsing data from impact craters, Naish and colleagues sought to measure the amount of organic molecules that could be transported from Titan’s organic-rich surface into the subsurface ocean.

Throughout its history, comets that collided with Titan melted the icy moon’s surface, creating pools of liquid water that mixed with organic matter on the surface. Because the resulting melt is denser than its icy crust, the heavier water likely sinks through the ice all the way to Titan’s subsurface ocean.

Using assumed collision rates with Titan’s surface, Naish and colleagues determined how many comets of different sizes would hit Titan each year throughout its history. This allowed the researchers to estimate the flow rate of water carrying organic matter moving from Titan’s surface into its interior.

Naish and his team found that the weight of organic matter transferred in this way was quite small, the amount of glycine, the simplest amino acid that is part of proteins in life, no more than 7,500 kg per year. This is about the same mass as a male African elephant. (All biomolecules, such as glycine, use the element carbon as the basis of their molecular structure.)

“One elephant a year releasing glycine into an ocean that is 12 times the volume of the world’s oceans is not enough to support life,” Naish said. “In the past, people often assumed that water equaled life, but they ignored the fact that life requires other elements, including carbon.”

Other icy worlds (such as Jupiter’s moons Europa and Ganymede and Saturn’s moon Enceladus) have almost no carbon on their surfaces, and it is unclear how much carbon can be extracted from their interiors. Titan is the most organically rich icy moon in the Solar System; Therefore, if the subsurface ocean is uninhabitable, this does not bode well for the habitability of other known icy worlds.

“This study shows that it is very difficult to transfer carbon from Titan’s surface to the subsurface ocean – in fact, it is difficult to have both water and the carbon necessary for life in the same place,” Naish said.

Dragonfly Flight

Despite the discovery, there is still much to learn about Titan, and the big question for Naish is what Titan is made of?

Naish is a researcher on NASA’s Project Dragonfly, a planned 2028 spacecraft mission that aims to send a robotic rotorcraft (drone) to Titan’s surface to study its prebiotic chemistry, or how organic compounds form and self-organize to give rise to life. is one. On Earth and beyond.

“It is nearly impossible to determine the composition of Titan’s organic-rich surface by observing it with a telescope through the organic-rich atmosphere,” Naish said. “We need to get down there and take samples from the surface to determine its composition.”

To date, only the international space mission Cassini-Huygens successfully landed a robotic probe on Titan in 2005 to analyze samples. It remains the first spacecraft to land on Titan and the furthest landing ever made by a spacecraft from Earth.

“Even if the subsurface ocean were uninhabitable, we could still learn a lot about prebiotic chemistry on Titan and Earth by studying reactions on Titan’s surface,” Naish said. “We really want to know if interesting reactions are happening there, especially where organic molecules mix with the liquid water produced during the impact.”

When Naish began his latest research, he was worried it would negatively impact Dragonfly’s mission, but it actually raised even more questions.

“If the entire impact collapses into the ice shell, we won’t have samples near the surface where water and organic matter mix. These are regions where Dragonfly can look for the products of these prebiotic reactions and give us information about how life might arise on different planets,” Naish said.

“The results of this study are much more pessimistic than I thought about the habitability of the ocean on Titan’s surface, but it also means there are more interesting prebiotic environments near Titan’s surface that we can study with the instruments on Dragonfly.”