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Last Updated: Monday, 22 March, 2004, 17:01 GMT
[41]E-mail this to a friend [42]Printable version
Detailed picture of comet's heart
By Dr David Whitehouse
BBC News Online science editor
A seething world of rock and ice
[43]Enlarge Image
The highest resolution image obtained by the Stardust spacecraft as it
flew by Comet Wild 2 in January has just been released by the US space
agency.
The image shows a pockmarked "flying mountain" strewn with jets of gas
and dust that billow in the solar wind.
As well as taking pictures, Stardust managed to capture and store
thousands of fresh cometary dust particles released from the object's
surface.
The probe will return this cargo to Earth for analysis in January
2006.
Active surface
The probe passed within 240km of Comet 81P/Wild 2 on Friday 2 January,
snapping 72 images and collecting a mass of data which scientists
continue to scrutinise.
Now, the mission team has put out a remarkable composite image of the
comet nucleus.
Stardust spacecraft, Nasa
Stardust will return its precious cargo in 2006
It is a short exposure image that shows tremendous surface detail,
overlain on a long exposure image taken just 10 seconds later that
reveals jets.
"This spectacular composite image shows a surface feature unlike any
other planetary surface seen to date in our Solar System," says
Professor Donald Brownlee, from the University of Washington.
"Other than our Sun, this is currently the most active planetary
surface in our Solar System, jetting dust and gas streams into space
and leaving a trail millions of km long.
"The overall shape of the nucleus resembles a thick hamburger with a
few bites taken out," says Thomas Duxbury, the Stardust Project
Manager, from Nasa's Jet Propulsion Laboratory.
"The surface has significant relief on top of this overall shape that
reflects billions of years of resurfacing from crater impacts and
out-gassing."
Stardust will bring samples of comet dust back to Earth to help answer
fundamental questions about the origins of the Solar System.
Floating snowballs
The remarkable image provides some clues about what it would be like
to walk on the surface of a comet.
Astronomers do not know the strength of the surface. When the comet is
active, some regions might be strong enough to support an astronaut;
elsewhere this individual could sink into a fluffy "snow".
Any visitor would not see very far because on such a small world the
horizon is very close.
Scientists say the probe took the best close-up pictures ever of a
comet
[44]Enlarge Image
Looking around, the astronaut would see a landscape of small hills, of
crumbling dust and occasionally huge depressions that are the
entrances to a vast subterranean network of constantly shifting
caverns.
On a comet, geysers of gas and dust erupt into space, many starting
their journey below the horizon. When they reach up into the sky, they
are twisted into curious spirals by the nucleus's spin.
Some geysers start in shadow and then dramatically burst into sunlight
as the jets are caught by the solar wind and are blown away from the
Sun.
At this stage of the comet's orbit, no stars would be visible to a
surface astronaut - the sky would be too full of glowing gas.
Stars would only be visible when the comet receded into the cold outer
Solar System where it would freeze and become a small inert world.
Hanging motionless
Gravity is slight, so an astronaut could jump into space and take
weeks to come back down again. They could watch the nucleus rotate
beneath them.
THE ROSETTA MISSION
The Rosetta mission, BBC
[45]Animated guide to the Rosetta mission
As well as gravity, other forces come into play because of the comet
nucleus's small size and rapid spin. The astronaut could stride to the
cometary equator where so-called Coriolis forces are apparent.
Throwing snowballs of cometary material into the air, the astronaut
would see these missiles curve in seemingly illogical directions. They
could even be tossed against the comet's spin and appear to hang
motionless in space.
No manned cometary landings are planned and probably never will be
because of the dangers involved. However, the unmanned Rosetta
spacecraft will release a small probe to touch down on Comet
67P/Churyumov-Gerasimenko in 2014.
[46]E-mail this to a friend [47]Printable version
LINKS TO MORE SCIENCE/NATURE STORIES
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SEE ALSO:
[48]Rosetta probe heads for comet
02 Mar 04 | Science/Nature
[49]Comet dust packed away for Earth
08 Jan 04 | Science/Nature
[50]Stardust probe makes comet flyby
02 Jan 04 | Science/Nature
[51]Probe returns asteroid image
05 Nov 02 | Sci/Tech
[52]Nasa reaches for stardust
08 Aug 02 | Sci/Tech
RELATED BBCi LINKS:
[53]Rosetta Timeline
RELATED INTERNET LINKS:
[54]Stardust
[55]Rosetta
[56]Comets
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