Cassini makes closest dive into Enceladus’ plumes

Artist’s concept of Enceladus’ icy plumes. NASA’s Cassini spacecraft completed its deepest-ever dive through it on Oct. 28, 2015. Image Credit: NASA/JPL-Caltech Enlarge

In an effort to better understand hydrothermal activity inside Saturn’s moon Enceladus, which is believed to harbor a global subsurface ocean, NASA’s Cassini spacecraft conducted a daring plunge into the moon’s icy plumes on Wednesday, Oct. 28. The spacecraft flew within 30 miles (50 km) of the moon’s surface, taking pictures and collecting samples that the Cassini scientists hope will answer questions about Enceladus’ habitability for primitive life.

The Cassini spacecraft, which was launched in 1997 and has been orbiting Saturn since 2004, has flown closer to Enceladus’ surface in the past, but has never flown into the active plumes.

Hydrothermal activity on Enceladus involves chemical reactions between rock and hot water. The process has implications for the possible existence of primitive life.

The towering plumes are composed of ice particles, water vapor, and organic molecules emerging from fractures in Enceladus’ south polar region. This area is marked by regions described as “tiger stripes”, which are much warmer than the rest of the moon’s surface and likely the areas from which water is escaping from below.

Cassini discovered the huge plumes soon after arriving at Saturn. The spacecraft also found Enceladus to be geologically active and to host a global underground ocean where hydrothermal activity is likely taking place.

The ocean is located between 18 and 24 miles (30–40 km) beneath the moon’s icy surface. That surface is young and relatively free of impact craters because of regular resurfacing by “water volcanoes”. The moon’s large plumes are speculated by scientists to emanate from this subsurface ocean.

The presence of this ocean and likely hydrothermal activity occurring there raise the possibility that Enceladus could host microbial life.

While the purpose of Cassini’s fly through the plumes is not to determine whether such life is present, the data expected to be obtained from the flyby is likely to indicate the degree to which Enceladus’ ocean is habitable for simple life forms.

Most important is the question of whether Cassini detects molecular hydrogen in Enceladus’ plumes

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