MIAMI • An unmanned Nasa spacecraft is about to make its deepest dive into the icy spray emanating from the underwater ocean on Saturn's moon, Enceladus.

The tiny moon orbiting the sixth planet from the Sun stunned scientists when they discovered it had an icy plume in 2005.

After years of observations, Nasa announced earlier this year that Enceladus has a subterranean ocean, widening the search for alien life in Earth's solar system.

While the Cassini probe's fly-by today will not be able to detect if there are life forms in the spray, scientists hope the close pass will give them new insight into the habitability of the extraterrestrial ocean.

"This daring fly-by will bring the spacecraft within 48km of the surface of Enceladus' south polar region," Nasa said in a statement. "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."

The fly-by should take place at 1522 GMT today (11.22pm Singapore time), though the scientific data it collects may not be published for months.

AGENCE FRANCE-PRESSE