These astronomers would like to know if liquid water exists on the moon Enceladus, possibly even contained in a large ocean.

NASA will tell Cassini to fly about 120 miles (190 kilometers) from the surface of Enceladus, which will place it on the edge of the plumes.

It its closest approach, Cassini will be only 30 miles (48 kilometers) from the moon’s surface. In terms of a spacecraft passing by a space body, this is like dipping its antenna into the pool. And, in this case, astronomers want to learn what materials compose that pool.

The sensors onboard Cassini will determine the size, density, speed, and composition of the particles and gases of the plumes.

Scientists are not exactly sure what gases make up the plumes, they think the gases include such gases as water vapor, carbon dioxide, methane, ammonia, and either carbon monoxide or nitrogen.

Sascha Kempf, deputy principal investigator for Cassini's Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, stated, “There are two types of particles coming from Enceladus, one pure water-ice, the other water-ice mixed with other stuff. We think the clean water-ice particles are being bounced off the surface and the dirty water-ice particles are coming from inside the moon. This flyby will show us whether this concept is right or wrong." [NASA]

There is little danger to the spacecraft at this close distance. Trajectory experts will make sure that Cassini doesn’t impact the moon. And, the particles in the geyser plume are so small they little chance of damaging the spacecraft. The ice-water particles contained in the plumes are thought to be about one ten-thousandth of an inch in diameter, or roughly the width of a human hair. In fact, Cassini crosses the path of much larger particles on a regular basis on its exploratory journey around Saturn and its moons.

Alan Stern, associate administrator of NASA’s Science Mission Directorate, states, “This daring flyby requires exquisite technical finesse, but it has the potential to revolutionize our knowledge of the geysers of Enceladus. The Cassini mission team is eager to see the scientific results, and so am I.” [NASA]

Learn more about the very interesting moon of Saturn: Enceladus. Please turn the page.