Saturn's majestic, iconic rings define the
planet, but where did they come from?
Kevin Grazier "Saturn's rings, good question.
And the answer is different depending on which
ring we're discussing."
That's Dr. Kevin Grazier, a planetary scientist
who worked on NASA's Cassini mission or over
15 years, studying Saturn's rings extensively.
Mike Brown "Saturn's rings - the strange things
about Saturn's rings is that they shouldn't
be there, really, in the sense that they don't
last for very long.
So, if they are just left over from when Saturn
was formed, they'd be gone by now.
They would slowly work their way into Saturn
and burn up and be gone.
And yet they're there.
So they are either relatively new or somehow
continuously regenerated.
'Continuously regenerated' seems strange and
'relatively new' seems also kind of strange.
Something broke up - a large moon broke up,
or a comet broke up - something had to have
happened relatively recently.
And by relatively recently, that means hundreds
of millions of years ago for someone like
me."
And that's Mike Brown, professor of planetary
geology at Caltech, who studies many of the
icy objects in the Solar System.
Saturn's rings start just 7,000 km above the
surface of the planet, and extend out to an
altitude of 80,000 km.
But they're gossamer thin, just 10 km across
at some points.
We've known about Saturn's rings since 1610,
when Galileo was the first person to turn
a telescope on them.
The resolution was primitive, and he thought
he saw "handles" attached to Saturn, or perhaps
what were big moons on either side.
In 1659, using a better telescope, the Dutch
astronomer Christiaan Huygens figured out
that these "handles" were actually rings.
And finally in the 1670s, the Italian astronomer
Giovanni Cassini was able to resolve the rings
in more detail, even observed the biggest
gap in the rings.
The Cassini mission, named after Giovanni,
has been with Saturn for almost a decade,
allowing us to view the rings in incredible
detail.
Determining the origin and evolution of Saturn's
rings has been one of its objectives.
So far, the argument continues:
Kevin Grazier "There's an age-old debate about
whether the rings are old or new.
And that goes back and forth - it's been going
back and forth for ages and it still goes
back and forth.
Are they old, or have they been there a long
period of time?
Are they new?
I don't know what to think, to be quite honest.
I'm not being wishy-washy, I just don't know
what to think anymore."
Evidence from NASA's Voyager spacecraft indicated
that the material in Saturn's rings was young.
Perhaps a comet shattered one of Saturn's
moons within the last few hundred million
years, creating the rings we see today.
If that was the case case, what incredible
luck that we're here to see the rings in their
current form.
But When Cassini arrived, it showed evidence
that Saturn's rings are being refreshed, which
could explain why they appear so young.
Perhaps they are ancient after all.
Kevin Grazier "If Saturn's rings are old,
a moon could have gotten too close to Saturn
and been pulled apart by tidal stresses.
There could have been a collision of moons.
It could have been a pass by a nearby object,
since in the early days of planetary formation,
there were many objects zooming past Saturn.
Saturn probably had a halo of material in
it's early days that was loosely bound to
the moon."
There is one ring that we know for certain
is being refreshed...
Kevin Grazier "The E-Ring, certainly a new
ring, because the E-Ring consists of roughly
micron-sized ice particles.
And micron-sized ice particles don't last
in space.
They sputter and sublimate - they go away
in very short time periods, and we knew that.
And so when we went to Saturn with Cassini,
we knew to look for a source of materiel because
we knew that the individual components of
the E-Ring don't last, so it has to be replenished.
So the E-Ring stands alone from the established
system, and the E-Ring is absolutely new."
In 2005, scientist discovered that Saturn's
E-Ring is being constantly replenished by
the moon Enceladus.
Cryovolcanoes spew water ice into space from
a series of fissures at its south pole.
So where did Saturn's rings come from?
We don't know.
Are the new or old?
We don't know.
It just another great mystery of the Solar
System.
