On its final mission before a fiery death, the Cassini satellite has helped discover two crucial building blocks for life in the atmosphere of Saturn's moon Titan.
Though it was discovered nearly 400 years ago, little was known about the moon until the Voyager and Cassini spacecraft observed it up close. And their discoveries placed Titan among the top contendors in the search for life beyond Earth. Though the moon has features similar to Earth—flowing liquids, puffy atmosphere—its chemistry vastly differs. Methane and ethane flow across the body's frosty surface and toxic compounds rain down from the sky, reports Nadia Drake for National Geographic.
Now, two studies published last week bolster the case for the possibility of life on Titan, and help explain how it might have evolved.
Using data from Cassini, the first study, published last week in the Journal of Astrophysical Letters, documents so-called carbon chain anions—negatively charged carbon molecules that are thought to serve as a step to the formation of more complex organic molecules that can develop life, reports Matt Williams of Universe Today.
"The discovery not only makes Titan a great contender for hosting some sort of primitive life, it also makes it the ideal place to study how life may have arisen from chemical reactions on our own planet," lead author of the study Ravi Desai, a planetary scientist at the University College in London, writes for The Conversation.
These carbon chain anions are akin to Legos that can be pieced together into larger molecules, reports Meghan Bartels for Mic. It also appears that these anions are being actively created even today as sunlight strikes Titan's upper atmosphere. "These [reactions] lead to larger organic compounds which drift downwards to form the moon’s characteristic 'haze' and the extensive dunes—eventually reaching the surface," writes Desai.
It's unusual to find similar negatively charged molecules like the ones found on Titan in "space environments," Desai writes. They tend to be quickly lost, combining with other molecules. "When present, however, they appear to be a crucial 'missing link' between simple molecules and complex organic compounds," he writes. The find may not only help shed light on possibilities for life on Titan, but also provide clues for how life arose on a Titan-like Earth billions of years ago.
A second study, published in the journal Science Advances, confirms the presence of a molecule Cassini previously detected in Titan's atmosphere with the potential to build cell membranes: vinyl cyanide.
Using radio telescopes based in Chile, researchers studied the toxic compound, reports JoAnna Wendel of Eos. This molecule, if it fell into the pools of liquid hydrocarbons on Titan's surface, could theoretically serve a role similar to that of phospholipids on Earth, which comprise the soft, but durable membranes surrounding all of our cells and their precious genetic material. While vinyl cyanide would be toxic to any life on our planet, the lack of water on Titan means that any life there would likely develop much differently than what we're familiar with, reports Wendel.
“Everything we have ever learned from planetary science tells us that other worlds are way more creative than we are,” Johns Hopkins University’s Sarah Hörst tells Drake.
Even so, the toxicity and the volatility of vinyl cyanide on our planet means that few researchers have studied the potential of these compounds in forming vital membranes, Drake reports. “We still are at the very beginning of the experimental work that’s really necessary to understand Titan’s lakes,” Hörst tells Drake.
As the craft prepares to plunge to its firey death in Saturn's atmosphere on September 15, scientists are vigilently working to tease through the immense data legacy the little-probe-that-could will leave behind. "Although we haven’t detected life itself, the presence of complex organic molecules at Titan, comets and within the interstellar medium means we are certainly coming close to finding its beginnings," Desai writes.