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Wow space stuff. Would make a neat setting for an SF story.
Saturn moon delights and baffles
By Jonathan Amos
BBC News science reporter
The tiger stripes mark the southern polar region of Enceladus
(Nasa/JPL/SSI)
More details
Space scientists say their discoveries about Saturn's moon Enceladus are
stunning, if just a little baffling.
Using the instrument-packed Cassini probe, they have confirmed that the
500km-wide world has an atmosphere.
They have also seen a "hotspot" at the icy moon's south pole, which is
riven with cracks dubbed "tiger stripes".
But the US and European scientists told a London meeting they could not
yet explain fully the energetic processes driving all the activity on
Enceladus.
"There were signs from a long time ago that Enceladus was a strange
moon," said Dr Carolyn Porco, leader of Cassini's imaging team, "but it is just
so gratifying and fabulous to see all the results come together and clearly
point to a specific region on the surface which seems to be the origin of a lot
of that peculiarity."
'Strange' world
The moon has become a major target of interest since the Cassini mission
to the Saturn system arrived just over a year ago.
Enceladus orbits the ringed planet at a distance of approximately
237,400km and is described as the most reflective object in the Solar System;
its icy surface throws back about 90% of the sunlight that hits it.
It would be like flying past the Earth and finding that Antarctica
was warmer than equatorial regions - that strange
Dr John Spencer, Southwest Research Institute
The spacecraft made a special low pass of the moon on 14 July, crossing a
mere 173km above the surface at its closest approach.
This allowed Cassini to make observations of unprecedented detail; and
they backed up data obtained by the probe's magnetometer instrument on previous
flybys that hinted at the presence of a water vapour atmosphere.
But that was just the start of what is now proving to be a fascinating
and evolving story.
"We confirmed the signature that there was an atmosphere but it is a
strange atmosphere," Professor Michele Dougherty, from the UK's Imperial
College and the lead scientist for the magnetometer instrument, told BBC News.
"It seems to be concentrated at the south pole and the best way to match
our observations is that you have almost a cometary jet coming off the south
pole."
'Hard to understand'
High-resolution imagery shows the southern polar region to be relatively
smooth - usually a good indicator of recent activity - but cut by a number of
long, dominant cracks. These are the so-called tiger stripes.
They are about 130km long and roughly parallel to one another, spaced
about 40km apart.
Cassini's composite infrared spectrometer shows the region to be much
warmer than expected.
Heat is concentrated at the south pole
Whereas temperatures near the equator are a frigid 80 Kelvin (minus
193C), the south polar average reaches 85K (minus 188C). Small areas of the
pole, concentrated near the tiger stripe fractures, are even warmer: well over
110K (minus 163C) in some places.
"The amount of heat there is really hard to understand as being due to
just sunlight warming the surface," said Dr John Spencer, from the Southwest
Research Institute in Colorado, US.
"It shouldn't be that warm at the pole. It would be like flying past the
Earth and finding that Antarctica was warmer than equatorial regions - that
strange.
"This is only the second place in the Solar System beyond Earth that
we've seen signs of heat coming out of the interior - the other being Jupiter's
moon Io."
The scientists think the cracks may act like vents, spewing out water
vapour and very fine water-ice particles. Some have suggested there could be
ice geysers and even ice volcanoes at the stripe locations - but these have not
been imaged directly.
Interest index
The puzzle for researchers is how to explain such an energetic system on
Enceladus.
As the moon moves around an eccentric orbit of Saturn, gravitational
forces should subject the tiny world to some tidal heating. Radioactive
isotopes in its rocky core may also be a source of some warming.
But scientists are struggling to make the numbers add up and are frankly
baffled as to why the activity they see should be so concentrated in just the
one region.
Cassini could detect very simple organics at the tiger stripes
"One of the most fascinating aspects of Enceladus is that it's so very
small as icy moons go, but so very geophysically active," said Dr Bob Brown,
from the University of Arizona, US, and team leader for Cassini's visual and
infrared mapping spectrometer.
"It's hard for a body as small as Enceladus to hold onto the heat
necessary to drive such large-scale geophysical phenomena, but it has done just
that.
"Enceladus and its incredible geology is a marvellous puzzle for us to
figure out."
Certainly, what the Cassini data has done is thrust Enceladus up the
interest index of objects in the Solar System that demand further
investigation.
Scientists may not be able to explain the "boiler" at the south pole but
they are already talking up the possibility that conditions there could allow
for liquid water below the surface - with all the implications that might have.
"It's quite likely that this moon will now join the ranks of Mars and
Jupiter's moon Europa where you might have liquid water - and the biologists
could start getting interested in this being a place were life might possibly
arise," enthused Dr Torrence Johnson, a Cassini scientist from Nasa's Jet
Propulsion Laboratory in California.
"It moves Enceladus from being a small denizen of the outer Solar System
- a frozen iceberg - to something that's more of an active type world that
we're interested in exploring."
Cassini discoveries at Enceladus include:
a.. presence of a strange atmosphere concentrated at the south pole
b.. atmosphere mostly (91%) water vapour, but with some nitrogen,
carbon dioxide and other simple carbon-based molecules (organics)
c.. large crevasse features at south pole dubbed tiger stripes
d.. intriguing hotspot at south pole - anomalous warmth in the area of
the tiger stripes
e.. presence of "orderly" water-ice at south pole, especially within
tiger stripe features, indicates region must have been very hot, be very young,
or both
f.. presence of simple organics along the fractures
g.. indication that water vapour and fine material are being ejected
from tiger stripes
h.. fine ice material is probably the significant and sustaining source
of ice particles that make up Saturn's outermost ring - its E ring
Cassini scientists are meeting in London this week ahead of a major
conference of the American Astronomy Society in Cambridge next week.
The $3.2bn Cassini-Huygens mission is a joint venture between the US
space agency (Nasa), the European Space Agency (Esa) and the Italian Space
Agency (Asi).
Size comparison - Earth to Enceladus. The moon is just 500km across
BBC NEWS:VIDEO AND AUDIO
See images sent back from the Cassini probe
MISSION TO SATURN
ANIMATED GUIDE
Destination Saturn
Watch how the Cassini mission to the ringed planet takes place
KEY STORIES
Enceladus delights and baffles
Saturn probe spies 'cheese' moon
Newest Saturn moons named
In pictures: Titan landing
Probe yields fresh images
Huygens probe lands on Titan
Titan moon 'geologically alive'
Cassini sends close-ups of rings
Phoebe is 'cosmic time capsule'
ANALYSIS
Titan: A glimpse into the unknown
RELATED BBC LINKS:
Radio 4: Running Rings Around Saturn
Solar System Tour
RELATED INTERNET LINKS:
Cassini-Huygens, Nasa JPL
Cassini-Huygens, Esa
Cassini Imaging Team
The Open University: Stardate - Mission to Titan
The BBC is not responsible for the content of external internet sites
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