The
formation of odd
spokes in Saturn's rings may depend on the amount of sunlight striking
the planet's ring plane, scientists said Thursday.
A new study
suggests that the spokes appear more often while Saturn's rings are edge-on to
the Sun, but fade out when the rings are completed tilted out at maximum
exposure.
"In fact, they
can be entirely switched off at times," said the University of Colorado's Mihály
Horányi, who led the study, of the spokes in an interview. "This is about the season they should start."
Horányi and
his team used images
and other data from the Cassini spacecraft currently studying the Saturnian
system to model how spokes rise and fall in the planet's ring system. The
research, which is detailed in the March 17 issue of the journal Science, predicts the spokes may return in force by July.
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NASA's Voyager spacecraft photographed spokes in Saturn's rings in the 1980s.
IMAGE: NASA/VOYAGER
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The spokes
in Saturn's rings intrigue astronomers, who believe the phenomenon may aid
investigations into the planet's magnetic field. They can reach 6,000 miles (9,656 kilometers) in length and span 1,500 miles (2,414 kilometers) in width, but their role and formation within the ring plane are not completely understood.
Saturn's
rings oscillate on a 15-year cycle as the planet circles the Sun, tilting open
at certain time while presenting themselves edge-on at others. According to Horányi's
model, Saturn's ring spokes appear to be active about eight years at a time,
followed by an absence of up to seven years.
Astronomers
caught their first close look of ring spokes during NASA's Voyager
mission, which swung past Saturn during the 1980s and returned images of
spokes forming rapidly - within five minutes at times - between subsequent
photographs.
"It's
almost amazing that you're discussing things that occur in seconds and minutes,"
Horányi said of the spokes. "Typically, we're always talking about things that
happen over millions of years."
Between
1998 and 2005, spoke searches with the Hubble Space Telescope came up empty-handed
and researchers believed that unlucky geometry between their Earth vantage
point, Saturn's ring plane and the Sun was to blame.
But when
Cassini entered orbit in 2004, the spokes remained
unseen. The orbiter finally
detected ring spokes in September 2005, which may be an indicator that a
new season of spoke activity is underway, researchers added.
"A lot of
us are very curious to see these again," Horányi said.
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