Poison gas hints at potential for life on Saturn’s moon Enceladus

Scientists have found poison in a spray of molecules emitted from Saturn’s small moon. That adds to the current intrigue about the possibility of living there.

The poison is hydrogen cyanide, a colorless gas that is dangerous to many living things on Earth. But it may have played a key role in the chemical reactions that created the materials that set the stage for the arrival of life.

“This is the starting point for most theories about the origin of life,” said Jonah Peters, a biophysics graduate student at Harvard. “It’s a kind of Swiss army knife of prebiotic chemistry.”

Thus, when he discovered hydrogen cyanide on Saturn’s icy moon Enceladus, Mr. Peter was excited, it’s about 310 miles across. It has an underground ocean, one of the most promising places to look for life elsewhere in the solar system.

At NASA’s Jet Propulsion Laboratory in California, Mr. Peter and his collaborators Tom Nordheim and Kevin Hand reported their findings in a paper published Thursday in the journal Nature Astronomy.

They also found organic molecules such as acetylene, propene and ethane that could fuel chemical reactions to provide energy for microbes living in Enceladus’ ocean. The data also indicated the presence of an alcohol such as methanol, although the researchers could not definitively identify which alcohol.

Chemical experiments show that hydrogen cyanide may be an important precursor to the molecules required for life to form. “It can be combined in a variety of ways to form amino acids, which are the building blocks of proteins and nuclear bases and sugars needed to make RNA and DNA,” said Mr. Peter said.

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Two decades ago, Enceladus was often seen as a bland snowball.

But in 2005, planetary scientists were startled when NASA’s Cassini spacecraft discovered steam and ice crystals pouring out of fractures near the moon’s south pole. Saturn’s tidal forces pull and squeeze Enceladus’ interior, and the friction creates enough heat to melt the ice.

Initial analysis identified not only water but also carbon dioxide, methane, hydrogen and ammonia. The eruptions pointed to hydrothermal reactions below the surface, where hot rocks meet liquid water.

Continued extraction of data from the Cassini mission, which ended in 2017, only added to the curiosity of what lies beneath. Scientists now believe that Enceladus has not only a pool of liquid water under its south pole, but also a global ocean of salty water under the outer ice sheet.

Earlier this year, another team of scientists reported the presence of phosphates in icy particles in Enceladus plumes, also pointing to geochemical interactions between the ocean and the rocky floor. Phosphorus is another important element considered essential for life.

“In fact, the chances for the development of life are getting better and better on Enceladus,” said Frank Bostberg, professor of planetary science at the Free University of Berlin, who led the phosphate study.

In a recent work, Mr. Peter and his collaborators again analyzed the data from the Cassini flybys. The amount of hydrogen cyanide is so small that it is not immediately noticeable. Instead, the researchers started a list of 50 compounds they thought might be present on Enceladus. They then made 10 to 15 models of those compounds, and tested which models best matched what Cassini observed.

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“It’s a good analysis to learn a little bit more about what we can see in the plumes,” said Kathleen Croft, a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Maryland.

Dr. For Kraft, Enceladus is an intriguing place but not the only place. Other moons orbiting Jupiter, such as Europa, also have oceans beneath the ice. An upcoming NASA mission, the Europa Clipper, will carry an instrument similar to Cassini’s that could make similar discoveries.

“All the sea worlds are very exciting,” Dr Croft said. “They all have slight differences from each other, but they have a lot in common.”

Researcher Alfonso D├ívila of the Exobiology Branch of NASA’s Ames Research Center in California said hydrogen cyanide and other newly reported organic compounds in Enceladus’ plumes “do not reveal a source of complex organic matter in the ocean.”

“But it’s an inch closer to the answer,” he said.

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