A NASA spacecraft will sample the ocean of Saturn's moon, Enceladus, when it flies through the moon's plume later.

Cassini will fly within 40 kilometres of the surface, and straight through the moons mysterious plumes - which are fuelled by a subsurface ocean that could potentially harbour life.

Cassini launched in 1997 and entered orbit around Saturn in 2004. Since then, it has been studying the huge planet, its rings and its magnetic field.

Early in its mission, Cassini discovered Enceladus has remarkable geologic activity - including a towering plume of ice, water vapour and organic molecules spraying from its south polar region.

Cassini later determined the moon has a global ocean and likely hydrothermal activity, meaning it could have the ingredients needed to support simple life.

Artist's impression of the possible interior of Enceladus based, on Cassini’s gravity investigation | Image: NASA/JPL-Caltech

However, NASA says this flyby is not intended to detect life "but it will provide powerful new insights about how habitable the ocean environment is within Enceladus".

The flyby will be Cassini's deepest-ever dive through the Enceladus plume, which is thought to come from the ocean below.

Scientists are hopeful the flyby will provide insights about how much hydrothermal activity - that is, chemistry involving rock and hot water - is occurring within the moon.

"This activity could have important implications for the potential habitability of the ocean for simple forms of life. The critical measurement for these questions is the detection of molecular hydrogen by the spacecraft", NASA adds.

Scientists also expect to better understand the chemistry of the plume as a result of the flyby.

The flyby should also help solve the mystery of whether the plume is composed of column-like, individual jets or icy curtain eruptions - or a combination of both.

Leo Enright is chairman of the Government's science awareness programme. He told Newstalk Breakfast this could be a big day for space exploration.