Cassini to fly thru encladus vapor

[radag...@gmail.com]

What with all the excitement this week, the Jules Verne ATV, the
Shuttle taking off.... Good things all, but this encounter will be
cool too. Way out Saturn's way, another small robot is busy.
Courtesy of Space.com .
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NASA's Cassini spacecraft circling the planet Saturn will plunge
through the outer fringes of an icy plume spewing out from cracks in
one of the ringed world's many moons on Wednesday.

Cassini will zip through the edges of immense frozen water vapor
geysers gushing from fractures in the south polar region of Saturn's
moon Enceladus. The flyby is Cassini's first of four swings past icy
Enceladus this year, where the spacecraft will use onboard instruments
to "sniff and taste" the satellite's Old Faithful-like water-ice
eruptions, mission managers said.

"This daring flyby requires exquisite technical finesse, but it has
the potential to revolutionize our knowledge of the geysers of
Enceladus," said Alan Stern, associate administrator of NASA's science
mission directorate, in a statement.

At its closest approach, Cassini will skim just 32 miles (52 km) above
the surface of Enceladus before passing through the moon's icy plume
at an altitude of about 120 miles (193 km). The spacecraft will zoom
past Enceladus at about 32,234 mph (51,875 kph), snapping photos
during on approach and departure that will return the first-ever views
of some northern regions, NASA officials said.

But Cassini will use particle analyzers during the flyby itself to
determine the exact make up of the moon's odd plume material, which
contains water vapor and traces of carbon dioxide, methane and other
gases.

"We want to know if there is a difference in composition of gases
coming from the plume versus the material surrounding the moon," said
Hunter Waite, principal investigator for Cassini's Ion and Neutral
Mass Spectrometer at the Southwest Research Institute. "This may help
answer the question of how the plume formed."

Cassini first spotted Enceladus' icy plume in 2005, when its onboard
instruments recorded water vapor geysers rushing out to distances of
up to three times the 310-mile (499-km) wide moon's diameter. The ice
particles themselves are tiny, just one ten-thousandth of an inch - or
about the size of the width of a human hair - but jet out of Enceladus
at about 800 mph (1,287 kph).

The apparently continuous eruptions appear to periodically give
Enceladus a fresh coat of surface material and spew out ice dust that
bolsters Saturn's faint E-ring.

Cassini researchers already know that there are at least two types of
particles - pure water-ice and water-ice intermixed with other
material - in Enceladus' plume.

"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," said Sascha Kempf, deputy principal investigator for Cassini's
Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics
in Heidelberg, Germany. "This flyby will show us whether this concept
is right or wrong."

Cassini mission managers will watch how their spacecraft weathers
Wednesday's Enceladus flyby to aid planning for additional swings past
the Saturnian moon. Cassini is due to make seven trips past Enceladus
during its extended mission, and could swing closer to the moon should
this weeks' rendezvous go well, NASA officials said.

From an article at Space.com .