This daring flyby will bring the Cassini spacecraft within 30 miles (48 kilometers) of Enceladus’ south pole.

Enceladus Flyby 'E-21': Deepest Dive Through the Plume

This daring flyby will bring the spacecraft within 30 miles (48 kilometers) of the surface of Enceladus’ south polar region. The flyby is Cassini's deepest-ever dive into the plume of icy spray that issues from fractures in the south polar region. The encounter will allow Cassini to obtain the most accurate measurements yet of the plume's composition, and new insights into the ocean world beneath the ice.

Enceladus is one of the most reflective bodies in the solar system because it is constantly coated by fresh, white ice particles.

Key scientific expectations for this flyby

Scientists are looking forward to several important scientific results from the Oct. 28 flyby. These results will not be available immediately -- they will take several months of careful analysis, and would be published in a peer-reviewed journal.

1. Confirm presence of molecular hydrogen (H2)

This measurement will be accomplished using Cassini's sensor that sniffs the gases in the plume (called INMS)

Confirmation of H2 would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus ocean, on the seafloor

Amount of H2 Cassini measures would reveal how much hydrothermal activity is going on in the ocean.

• This has implications for the amount of energy available for creating a habitable environment in the ocean

2. Better understand the chemistry of material in the plume

Cassini's dust detector (called CDA) will obtain spectra of the heavier particles only found at low altitudes nearer to the plume's source

• Among these heavier particles, Cassini may detect new, more complex organic molecules (albeit with not enough resolution to confirm if they are biological in nature)

• Scientists think these heavier particles carry material from the sub-surface ocean

• Scientists are doing laboratory experiments to create a catalog they can refer to of chemical fingerprints (or spectra) for fragments of complex organic molecules Cassini might detect

3. Determine the nature of the plume sources

Is the plume made up of tight, column-like jets or curtain-like eruptions that run along the length of the tiger stripe fractures (or both)?

How much icy material are the plumes actually spraying out? Scientists are still not sure, and the amount has major implications for how long the moon might have been active.

This measurement will be accomplished by part of Cassini's CDA instrument called the high-rate detector, which can count the impacting ice particles from the plume (over 10,000 per second) in real-time.

Important points about the encounter