- A delicate new ring and possibly two new moons have been
spotted around Saturn by the US-European Cassini mission, astronomers
announced
Thursday.
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- Astronomers at Queen Mary University of London, UK,
detected
a faint dust ring 300 kilometres wide in images taken by the spacecraft
since July 2004. The ring lies 1200 km beyond the main ring system, between
the bright, wide A ring and the faint, outermost F ring. It has been seen
in an arc spanning about a tenth of the rings' circumference and may extend
all the way around the planet.
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- Its location coincides with that of Saturn's moon Atlas,
suggesting the moon is shedding pieces of itself as it collides with
micrometeorites
in its orbit. "The ring is being constantly replenished," team
member Mike Evans told New Scientist, likening the process to the two moons
thought to cause Jupiter's dusty ring.
-
- His team also discovered an object about four kilometres
across orbiting 1000 km beyond the F ring. Astronomers measuring its
brightness
cannot determine if the object is solid, making it a small moon, or simply
a puff of dust created by a collision of space rocks or gravitationally
stirred up by the approach of one of Saturn's moons.
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- Inside out
-
- The mystery object, called S/2004 S3, grew even more
intriguing when Joe Spitale at the Space Science Institute in Boulder,
Colorado, computed its orbit in an attempt to spot it in other
images.
-
- He found a similar object in images taken about five
hours after the first sighting, in generally the right area around Saturn.
But instead of being outside the F ring as before, the object he saw was
several hundred kilometres away inside the F ring.
-
- "If this is the same object, then it has an orbit
that crosses the F ring, which makes it a strange object," he says.
That strangeness means the object he found is also being tentatively
considered
as new and called S/2004 S4.
-
- But Evans says there could be a straightforward
explanation
of how a moon could cross the narrow F ring. "Maybe the moon or clump
could have the same elliptical shape of orbit as everything else in [the
ring] but the orientation could be completely different," he
says.
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- The orientation of orbits change constantly around Saturn
because the planet, like most spinning bodies, is slightly wider than it
is tall. The speed at which orbits change, or precess, depends on their
distance from the planet, so the moon could cross the F ring if the two
are precessing at slightly different rates.
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- In August, French astronomers found two similarly small
moons around Saturn, which previously had a total of 33 known moons.
Cassini
slipped into orbit around the planet in July.
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- http://www.newscientist.com/news/news.jsp?id=ns99996382
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