No. 5000 ... Enceladus/Chapter II

An artist’s impression of plumes spewing from the tiger stripes on Enceladus. Image credit: Graphic composition (Image credit: NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute).

A tiny moon, orbiting Saturn, might be the one harboring life in our solar system if all the essential organics seen thus far combine and do their thing to finally put an end to the age old question,

Is their life out there? 

Complex organic molecules that form part of the chain of chemical reactions that can result in life's building blocks have been found in the watery geysers of Enceladus, almost twenty years after the plumes were first sampled by NASA's Cassini spacecraft.

Cassini's mission to the ringed planet Saturn ended in 2017, but scientists are still making findings buried deep in its treasure trove of archived data.

The discovery of these organic molecules ("organic" meaning they contain carbon) strengthens the case for the icy moon Enceladus being of astrobiological interest. In 2005, Cassini discovered that plumes of water vapor were spraying into space from huge fissures in Enceladus' surface. These fissures are believed to lead to a subsurface ocean within the 310-mile-wide (500-kilometer-wide) moon of Saturn, and it is this ocean that provides the water for the plumes. While some of the material from the plumes snows back onto the surface of Enceladus, most of it escapes into space where it forms a diffuse ring, called the E-ring, encircling Saturn at a greater distance from the planet than most of the rest of its system of rings.

Enceladus orbiting within Saturn's E ring

However, Cassini also flew directly through some of the plumes, so Khawaja went back to archive data from 2008 and the results from the spacecraft's Cosmic Dust Analyzer (CDA), which was an instrument led by scientists at the University of Stuttgart. With painstaking precision, Khawaja's team took apart the CDA data, and their new analysis found evidence for organic molecules that had been missed the first time around.

When Cassini flew through the plumes, icy grains struck the CDA's detector at 11 miles (18 kilometers) per second, which is faster than the 7.5 miles (12 kilometers) per second in the E-ring. These grains, only just spewed out of the ocean, contain pristine material that had not yet been altered by radiation.

"The ice grains contain not just frozen water, but also other molecules including organics," said Khawaja. "At lower impact speeds, the ice shatters and the signal from clusters of water molecules can hide the signal from certain organic molecules. But when the ice grains hit the CDA fast, water molecules don’t cluster and we have a chance to see these previously hidden signals."

The results showed that the same organic molecules present in the E-ring are also in the plumes, which tells scientists that they must originate from the ocean and are not a product of space radiation. Khawaja's team also found a variety of other organic molecules that had not been detected before in relation to Enceladus' plumes. These include aliphatic, (hetero)cyclic ester/alkalines, ethers/ethyl and possibly nitrogen- and oxygen-bearing compounds. On Earth, these molecules are part of a chain of chemical reactions that lead to life's building blocks.

An infographic showing various molecules moving through a labeled ocean
toward a reddish-brownish surface labeled water-filled core.

"There are many possible pathways from the organic molecules we found in the Cassini data to potentially relevant compounds, which enhances the likelihood that the moon is habitable," said Khawaja.

No. 5000 seems appropriate, does it not? :)