Saturn’s moon Enceladus has a subsurface ocean – and it may be coated with complex organic molecules that could be stepping stones to life.
Plumes of liquid water from the ocean spurt out of Enceladus’ southern regions and can fly high enough to escape the small moon’s gravity. Some of this material actually ends up around Saturn, forming its diffuse E ring.
During the course of its mission, the Cassini spacecraft flew through both the plumes and the E ring, collecting samples of ice grains and frozen organic molecules. Frank Postberg at Heidelberg University in Germany and his colleagues have analysed the data from Cassini to learn more about these molecules.
Advertisement
The instruments on the spacecraft weren’t built for this – they were designed decades before we knew that Enceladus had plumes – so Postberg and his team had limited information to work with. They could determine the masses of the molecules and infer what elements they were made of, but not much else.
Large molecules
The researchers found organics made of carbon, hydrogen, and nitrogen that were far larger than anything we’ve seen on Enceladus before. We had only seen molecules with masses up to 50 atomic mass units, but Postberg and his team found some that were more than four times larger.
The structures of those molecules – chains and rings of carbon atoms – indicates that they are actually fragments of even bigger, more complex compounds. The researchers say that after being produced at Enceladus’ rocky core, the compounds hitch a ride on the outside of rising gas bubbles to form a rich organic film on the ocean’s surface. More bubbles then pop and send them spraying upwards in the plumes.
“We know that process works on much smaller scales in Earth’s ocean – these gas bubbles are really good at harvesting organic stuff,” says Postberg.
Molecules this big and complicated may have been produced by life, but it’s equally likely that they came from rock interacting with hot water in Enceladus’ core, Postberg says.
Even so, they might be an important ingredient in the development of life. “For the most part the things that are really important for life – the proteins, the DNA, the things that encode information – are bigger molecules,” says Kelly Miller at the Southwest Research Institute in Texas.
Studying the complex molecules in the plumes further could help us understand how likely it is that icy worlds like Enceladus could host life. “And if we’re interested in looking for the origins of life, then understanding where these macromolecules are present and how they evolve is important,” says Miller. “One of those evolutionary paths led to life on Earth.”
Nature
