A new analysis of data from NASA’s Cassini mission found evidence of previously undetected organic compounds in a plume of ice particles ejected from the ocean that lies under the frozen shell of Saturn’s moon Enceladus. Researchers spotted not only molecules they’ve found before but also new ones that lay a potential path to chemical or biochemical activity.
The ice grains studied were collected just 13 miles (21 kilometers) from the moon’s surface and mark the first time scientists have observed this diversity of organics in fresh particles ejected from the subsurface water of Enceladus. Published Wednesday in Nature Astronomy, the findings signal an important step toward confirming active organic chemistry below the moon’s surface. This is the kind of chemical activity that could support compounds that are important to biological processes and are an essential component of life on Earth.
Besides increasing the diversity of detected organics, the recent work added a new layer to earlier findings by analyzing particles that the Cassini spacecraft collected when it flew directly through a plume — the next-best thing to diving directly into the moon’s ocean.
“Previously, we detected organics in ice grains that were years old and potentially altered by the intense radiation environment surrounding them,” said Nozair Khawaja of the Freie Universität Berlin, lead author of the study. “These new organic compounds were just minutes old, found in ice that was fresh from the ocean below Enceladus’ surface.”
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Scientists knew from previous Cassini data-mining that nitrogen- and oxygen-bearing organic compounds were present in particles from Saturn’s E ring, a faint, wide outer band around the planet fed by the icy material that fans out from Enceladus’ plumes. But the new research analyzed ice grains from a moon plume itself — in other words, grains found closest to their subsurface origin.
“These molecules we found in the freshly ejected material prove that the complex organic molecules Cassini detected in Saturn’s E ring are not just a product of long exposure to space, but are readily available in Enceladus’ ocean,” said coauthor Frank Postberg, also of Freie Universität Berlin.
Fast and fruitful
The data was collected and sent to Earth in 2008, when ice particles impacted Cassini’s Cosmic Dust Analyzer instrument. Besides being directly sourced from a plume, the ice grains had another thing going for them: They’d been smashed to smithereens as they struck the instrument during the spacecraft’s fast fly-through at 11 miles per second (about 18 kilometers per second relative to the moon).
The energy of the impact vaporized the ice grains and ionized a substantial fraction of them. Those ions were then analyzed by the instrument’s mass spectrometer, which examined their chemical makeup.
The study’s authors were able to analyze the tiniest of fragments — smaller than a thousandth of a millimeter, smaller even than a flu virus — and identify organic compounds they hadn’t seen before in plume particles.
The newly detected compounds included those from the aliphatic and cyclic ester and ether families, some with double bonds in their molecular structures. Together with the confirmed aromatic, nitrogen- and oxygen-bearing compounds, these compounds can form the building blocks to support chemical reactions and processes that could have led to more complex organic chemistry — the kind that is of interest to astrobiology and narrows the focus of where we search for life in the solar system.
After flying through the plume, the spacecraft, managed by NASA’s Jet Propulsion Laboratory in Southern California, explored the complex Saturn system for nearly another decade.
More about Cassini
The Cassini-Huygens mission was a cooperative project of NASA, ESA (European Space Agency), and the Italian Space Agency. A division of Caltech in Pasadena, JPL managed the mission for NASA’s Space Mission Directorate in Washington and designed, developed, and assembled the Cassini orbiter.
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