Scientists Study 'Plumbing' in Plumes of Enceladus
- From: baalke@xxxxxxxxxxxxx
- Date: Thu, 7 Feb 2008 18:10:50 -0800 (PST)
http://www.jpl.nasa.gov/news/features.cfm?feature=1597
Scientists Study 'Plumbing' in Plumes of Enceladus
Jet Propulsion Laboratory
February 07, 2008
Scientists on the Cassini mission have become out-of-this world
"plumbers" as they try to piece together what's happening inside the
"pipes" feeding the plumes of Saturn's moon Enceladus.
Enceladus is jetting out giant geysers three times the size of the
moon,
and now scientists are beginning to understand how the ice grains are
created and how they might have formed. Knowing the process of how the
plume forms and the path the water-ice particles have to travel is
giving them an insight into what may be a liquid reservoir or lake
lying
just beneath the surface.
"Since Cassini discovered the water vapor geysers, we've all wondered
where this water vapor and ice are coming from. Is it from an
underground water reservoir or are there some other processes at work?
Now, after looking at data from multiple instruments, we can say there
probably is water beneath the surface of Enceladus," said Juergen
Schmidt, team member on Cassini's Cosmic Dust Analyzer at the
University
of Potsdam, Germany. This study appears in the Feb. 7, 2008, issue of
the journal Nature.
The large number of ice particles observed spewing from the geysers
and
the steady rate at which these particles are produced require high
temperatures, close to the melting point of ice, possibly resulting in
an internal lake. The lake would be similar to Earth's Lake Vostok,
beneath Antarctica, where liquid water exists locked in ice. The ice
grains then condense in the vapor evaporating from the water,
streaming
through cracks in the ice crust to the surface.
The presence of liquid water inside Enceladus would have major
implications for future astrobiology studies on the possibility of
life
on bodies in the outer solar system.
Scientists have studied the plume dynamics since 2005, collecting data
from several Cassini remote sensing instruments and those that sample
particles directly, like the Cosmic Dust Analyzer. They conclude that
an
internal lake at a temperature of about 273 Kelvin (32 degrees
Fahrenheit) is the best way to account for the material jetting out of
the geysers.
At these warm temperatures, liquid water, ice and water vapor mingle.
The vapor escapes to the vacuum of space through cracks in Enceladus'
ice crust. When the gas expands, it cools and the ice grains that make
up the visible part of the plumes condense from the vapor. Vapor in
the
plumes is clocked at roughly the same speed as a supersonic jet, about
300 to 500 meters per second, or about 650 to 1,100 miles per hour.
However, most of the condensed ice particles fail to reach Enceladus'
escape velocity of 240 meters per second (536 miles per hour).
Pinball-like physics account for the slow speed of the particles.
Shooting up through crooked cracks in the ice, the particles ricochet
off the walls, losing speed, while the water vapor moves unimpeded up
the crevasse. The vapor reboosts the frozen particles as they pinball
off the walls, carrying them upward. Reaching nozzle-like openings at
the surface, the faster-moving water vapor shoots high above
Enceladus,
becoming entrapped in Saturn's magnetosphere. Most of the particles,
which have lost energy through collisions in transit, fail to achieve
escape velocity and fall back to Enceladus' surface. Only about 10
percent escape Enceladus and form Saturn's E-ring.
"Our model provides a simple concept to understand how particles form,
their speed and how they behave as they make their way out into space.
If vapor temperature is too low, then the gas density is too small to
push the grains out and we would not see such large amounts of
particles," said Schmidt. "Therefore, we believe that at the site of
evaporation, we must have temperatures near the melting point of
water."
Scientists say that particles seen in the plumes are too numerous to
have started from processes described in one existing model that
requires low temperatures, proposing that gases may be trapped inside
ice crystals. Another model suggests that water ice, suddenly exposed
to
the vacuum of space, sublimes, or boils, directly into vapor without
liquefying first. But this would mean there are short bursts of
activity, rather than the steady production of particles. The new
model
of grains condensing in a vent that evaporates from a liquid body is
consistent with a steady production of particles, ejected from a
localized source.
This research provides fundamental knowledge about solar system
bodies,
in particular those that, like our home planet, are homes to oceans -
environments where life might evolve.
The next Enceladus flyby is in March 2008. The spacecraft closest
approach will be at a mere 50 kilometers (30 miles) from the surface
and
the altitude will increase to about 200 kilometers (124 miles) as the
spacecraft passes through the plumes. Cassini will sample the plumes
directly and find out more about their makeup.
More information on the Cassini-Huygens mission is available at:
http://saturn.jpl.nasa.gov and
http://www.nasa.gov/cassini .
The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena, manages the
Cassini
mission for NASA's Science Mission Directorate, Washington, D.C. JPL
designed, developed and assembled the Cassini orbiter.
------------------------------------------------------------------------
Media contact: Carolina Martinez/JPL 818-354-9382
.
- Prev by Date: MESSENGER Team Begins Planning for Second Mercury Encounter
- Next by Date: Mars Exploration Rover Update - February 6, 2008
- Previous by thread: MESSENGER Team Begins Planning for Second Mercury Encounter
- Next by thread: Mars Exploration Rover Update - February 6, 2008
- Index(es):
Relevant Pages
|
